Current sensor, inverter circuit, and semiconductor device having the same转让专利
申请号 : US13150764
文献号 : US08791690B2
文献日 : 2014-07-29
发明人 : Satoshi Shiraki , Norihito Tokura , Shigeki Takahashi , Masahiro Yamamoto , Akira Yamada , Hiroyasu Kudo , Youichi Ashida , Akio Nakagawa
申请人 : Satoshi Shiraki , Norihito Tokura , Shigeki Takahashi , Masahiro Yamamoto , Akira Yamada , Hiroyasu Kudo , Youichi Ashida , Akio Nakagawa
摘要 :
权利要求 :
What is claimed is:
说明书 :
This application is based on and claims priority to Japanese Patent Application No. 2010-129319 filed on Jun. 4, 2010, No. 2011-15345 filed on Jan. 27, 2011, and No. 2011-27411 filed on Feb. 10, 2011, the contents of which are incorporated herein by reference.
The present invention relates to a semiconductor device having a main cell and a sense cell for detecting an electric current flowing through the main cell.
U.S. Pat. No. 5,253,156 corresponding to JP-A-8-34709 discloses a semiconductor integrated circuit including a main cell having a lateral insulated gate bipolar transistor (IGBT) and a current detector (hereafter referred to as “sense cell”) for detecting an electric current flowing through an emitter of the IGBT. The sense cell has a lateral IGBT with the same structure as the lateral IGBT of the main cell except the length of the emitter. The IGBTs are coupled in a current mirror configuration so that an electric current flowing through the emitter of the IGBT of the sense cell becomes smaller than the electric current flowing through the emitter of the IGBT of the main cell by a predetermined ratio that depends on the ratio between the lengths of the emitters. Thus, the current flowing through the main cell can be detected based on the current flowing through the sense cell.
However, when the semiconductor integrated circuit disclosed in U.S. Pat. No. 5,253,156 is used to form a circuit shown in
In the circuit shown in
Such a problem can occur in a semiconductor element other than an IGBT.
By the way, such a circuit shown in
In view of the above, it is an object of the present invention to provide a semiconductor device having an inverter circuit and a current sensor for detecting value and direction of an electric current.
According to a first aspect of the present invention, a semiconductor device with a lateral semiconductor element includes a semiconductor substrate, a first electrode on a surface of the substrate, a second electrode on the surface of the substrate, and an isolation structure located in the substrate to divide the substrate into a first island and a second island. The first and second islands are electrically insulated from the each other by the isolation structure. The lateral semiconductor element includes a main cell located in the first island and a sense cell located in the second island. The main cell causes a first current to flow between the first electrode and the second electrode so that the first current flows in a lateral direction along the surface of the substrate. The first current is detected by detecting a second current flowing though the sense cell.
According to a second aspect of the present invention, a semiconductor device with a lateral IGBT for controlling supply of an electric current to a load includes a semiconductor substrate having a first conductivity-type drift layer, a second conductivity-type collector region located in a surface portion of the drift layer and having a longitudinal direction, a second conductivity-type channel layer located in the surface portion of the drift layer and having a straight portion extending parallel to the collector region, and an emitter region located in a surface portion of the channel layer and terminated inside the collector region. The emitter region has a straight portion extending in the longitudinal direction. The semiconductor device further includes a gate insulating layer located on a channel region of the channel layer. The channel region is located between the emitter region and the drift layer. The semiconductor device further includes a gate electrode located on the gate insulating layer, a first electrode electrically connected to the collector region, and a second electrode electrically connected to the emitter region and the channel layer. The emitter region is divided to form a main cell and a sense cell, each of which has the lateral IGBT. The lateral IGBT of the main cell is configured to control the supply of the electric current to the load. The lateral IGBT of the sense cell is identical in structure to the lateral IGBT of the main cell and configured as a current detector. The main cell is located on each side of the sense cell so that the sense cell is located in the main cell in the longitudinal direction.
According to a third aspect of the present invention, a current sensor for detecting an electric current in a current path connected to a load includes a power element located in the current path and turned ON and OFF to control the electric current. The electric current flows through the power element in a forward direction, when the power element is turned ON. The current sensor further includes a freewheeling diode located in the current path and connected in antiparallel with the power element. The electric current flows through the freewheeling diode in a backward direction, when the power element is turned OFF from ON. The current sensor further includes a first sense cell connected to the power element in such a manner that the electric current flowing through the first sense cell is in proportional to the electric current flowing through the power element. The current sensor further includes a first sense resistor connected in series with the first sense cell. The current sensor further includes a second sense cell connected to the freewheeling diode in such a manner that the electric current flowing through the second sense cell is in proportional to the electric current flowing through the freewheeling diode. The current sensor further includes a second sense resistor connected in series with the second sense cell.
The above and other objects, features, and advantages will become more apparent from the following description and drawings in which like reference numerals depict like elements. In the drawings:
A semiconductor device having a lateral insulated gate bipolar transistor (IGBT) according to a first embodiment of the present invention is described below with reference to
According to the first embodiment, as shown in
The SOI substrate 1 includes a supporting substrate 1a, a buried oxide (BOX) layer 1b on the supporting substrate 1a, and an active layer 1c on the BOX layer 1b. For example, the supporting substrate 1a can be a silicon substrate. According to the first embodiment, the active layer 1c serves as an n−-type drift layer 2. Each part of the lateral IGBTs of the main cell and the sense cell is formed in a surface portion of the drift layer 2.
The thickness of the BOX layer 1b, and the thickness and the impurity concentration of the active layer 1c (i.e., drift layer 2) are not limited to specific values and can vary depending on the intended use of the semiconductor device. For example, in order to achieve high breakdown voltage, it is preferable that the thickness of the BOX layer 1b be 4 micrometers (μm) or more. In order to ensure a breakdown voltage of 600V or more, it is preferable that the thickness of the BOX layer 1b be 5 μm or more. In order to ensure the breakdown voltage of 600V or more, it is preferable that the active layer 1c have the n-type impurity concentration of from 1×1014 cm−3 to 1.2×1015 cm−3, if the thickness of the active layer 1c is 15 μm or less. In order to ensure the breakdown voltage of 600V or more, it is preferable that the active layer is have the n-type impurity concentration of from 1×1014 cm−3 to 8×1014 cm−3, if the thickness of the active layer 1c is 20 μm.
Trench structures 1d are formed in the active layer 1c is to divide the active layer is into multiple islands that are electrically isolated from each other. The main cell and the sense cell are located in different islands and thus electrically insulated from each other. For example, the trench structure 1d can be formed by forming a trench extending through the active layer 1c is to the BOX layer 1b, by forming an oxide layer on an inner surface of the trench by thermal oxidation, and then by filling the trench with polysilicon or the like.
A LOCOS (LOCal Oxidation of Silicon) oxide layer 3 is formed on a surface of the drift layer 2. The parts of the lateral IGBT are electrically insulated from each other by the LOCOS oxide layer 3. A p+-type collector region 4 is formed in the surface portion of the drift layer 2 and exposed outside the LOCOS oxide layer 3. The collector region 4 has a longitudinal direction parallel to a surface of the SOI substrate 1. The collector region 4 is surrounded by an n-type buffer layer 5. The buffer layer 5 has an impurity concentration greater than that of the drift layer 2.
A p-channel well layer 6, an n+-type emitter region 7, a p+-type contact layer 8, and a p-type body layer 9 are formed in the surface portion of the drift layer 2 and exposed outside the LOCOS oxide layer 3. The well layer 6, the emitter region 7, the contact layer 8, and the body layer 9 are arranged around the collector region 4.
A surface portion of the well layer 6 serves as a channel region. For example, the well layer 6 can have a thickness of 2 μm or less and a width of 6 μm or less. As shown in
The emitter region 7 is formed in a surface portion of the well layer 6 and terminated inside the well layer 6. The emitter region 7 extends in the longitudinal direction of the collector region 4. According to the first embodiment, as shown in
The contact layer 8 fixes the well layer 6 to an emitter potential and has an impurity concentration greater than that of the well layer 6. As shown in
The body layer 9 reduces a voltage drop caused by a Hall current flowing from a collector to an emitter. The body layer 9 has a straight portion extending in the longitudinal direction of the collector region 4 (and the collector electrode 12). The body layer 9 is arranged circularly around the collector region 4 so that the collector region 4 can be singly surrounded by the body layer 9. The body layer 9 reduces or prevents operation of a parasitic npn transistor, which is constructed with the emitter region 7, the well layer 6, and, the drift layer 2. Thus, turn-off time can be improved. In this way, the well layer 6, the contact layer 8, and the body layer 9 are concentrically arranged around the collector region 4.
In each cell, as shown in
A gate electrode 11 is located on a surface of the well layer 6 through a gate insulating layer 10. For example, the gate electrode 11 can be made of doped polysilicon. The surface portion of the well layer 6 becomes the channel region by applying a voltage to the gate electrode 11.
A collector electrode 12 is located on and electrically connected to the collector region 4. An emitter electrode 13 is located on and electrically connected to the emitter region 7 and the contact layer 8.
Further, according to the first embodiment, a resistor layer 14 serving as a field plate is formed on the LOCOS oxide layer 3 between the collector and the gate. For example, the resistor layer 14 can be made of doped polysilicon. The resistor layer 14 serves to maintain a uniform potential gradient between the collector and the gate. Specifically, as shown in
As shown in
The lateral IGBT according to the first embodiment operates as follows. When a predetermined voltage is applied to the gate electrode 11, the channel region appears in the surface portion of the well layer 6, which is located below the gate electrode 11 between the emitter region 7 and the drift layer 2. Electrons flow from the emitter electrode 13 and the emitter region 7 into the drift layer 2 through the channel region. Accordingly, holes flow into the drift layer 2 through the collector electrode 12 and the collector region 4. Thus, conductivity modulation occurs in the drift layer 2 so that a large current can flow between the emitter and the collector. In this way, the lateral IGBT operates.
According to the first embodiment, the IGBTs of the main cell and the sense cell are identical in structure and coupled in a current mirror configuration so that an electric current flowing through the emitter of the IGBT of the sense cell becomes smaller than the electric current flowing through the emitter of the IGBT of the main cell by a predetermined ratio that depends on a ratio between areas of the IGBTs (specifically, a ratio between the lengths of the emitters). Thus, the current flowing through the main cell can be detected based on the current flowing through the sense cell. The electric current flowing through the sense cell is detected by detecting a voltage across the sense resistor Rs connected between the emitters of the main cell and the sense cell.
Assuming that the lateral IGBT is used as a high breakdown voltage device in which a high voltage of 100V or more is applied to its collector, a collector potential changes between 0V and 100V during switching operation. Due to coupling with the high voltage, noise is induced at an output terminal used for current detection. Therefore, it is difficult to accurately detect a current. When a resistance of the sense resistor Rs is increased to increase the voltage across the sense resistor Rs, a PN junction formed between the body layer 9 and the drift layer 2 is forward biased. As a result, a parasitic transistor operates so that an output (i.e., the voltage across the resistor Rs) becomes unstable. Further, since the potential of the resistor layer 14 changes during the switching operation, the resistor layer 14 can act as a source of noise. Therefore, it is difficult to accurately detect the current.
In order to overcome the above problem, according to the first embodiment, the main cell and the sense cell are electrically insulated from each other by the trench structure 1d. In such an approach, even when the high voltage of 100V or more is applied to the collector of the main cell, noise induced at the output terminal can be reduced or prevented. Further, even when the emitter potential of the sense cell rises due to the current flowing through the sense resistor Rs, the parasitic transistor is inoperative because of the electrical insulation between the main cell and the sense cell. For the same reason, it is less likely that the resistor layer 14 acts as a source of noise. Therefore, the current flowing through the main cell can be accurately detected, even when the lateral IGBT is used as a high breakdown voltage device.
It is noted that noise resistance can be improved by increasing the amount of current flowing through the sense cell. For example, when the area of the sense cell is from one-fifth to one-hundredth of the area of the main cell, the amount of current flowing though the sense cell becomes large enough to ensure a high noise resistance.
A semiconductor device according to a second embodiment of the present invention is described below with reference to
According to the second embodiment, as shown in
As shown in
A cathode electrode 28 and an anode electrode 29 are formed on the surface of the SOI substrate 21. The cathode electrode 28 is electrically connected to the contact layer 24. The anode electrode 29 is electrically connected to the contact layer 27 and the anode layer 26. Further, a resistor layer 30 is formed on the LOCOS oxide layer 23 between the anode and the cathode. For example, the resistor layer 30 can be made of doped polysilicon. The resistor layer 30 serves to maintain a uniform potential gradient between the anode and the cathode. Specifically, as shown in
As described above according to the second embodiment, the FWD of the main cell and the FWD of the sense cell are located on different islands that are electrically insulated from each other by the trench structure 21d. For example, the sense resistor Rs can be connected between the anodes of the main cell and the sense cell, and the cathodes of the main cell and the sense cell can be connected together. In such an approach, an electric current flowing through the main cell can be detected by detecting an electric current flowing through the sense cell based on a voltage across the sense resistor Rs.
Even when a high voltage of 100V or more is applied to the cathode of the main cell, noise induced at an output terminal used for current detection can be reduced or prevented. Further, even when an anode potential of the sense cell rises due to the current flowing through the sense resistor Rs, the parasitic transistor is inoperative because of the electrical insulation between the main cell and the sense cell. For the same reason, it is less likely that the resistor layer 30 acts as a source of noise. Therefore, the current flowing through the main cell can be accurately detected, even when the lateral FWD is used as a high breakdown voltage device.
A semiconductor device according to a third embodiment of the present invention is described below with reference to
As shown
The circuit shown in
A method of detecting the magnitude and direction of the current flowing through the current path leading to the lateral IGBT or the lateral FWD is described below with reference to
When the lateral IGBT is turned ON, the current flows from the collector to the emitter of the lateral IGBT, as shown in
Then, when the lateral IGBT is turned OFF from ON, a reverse recovery current flows through the lateral FWD, as shown in
Then, the recovery current becomes zero after a lapse of a certain period of time. As a result, no current flows through the lateral IGBT and the lateral FWD, as shown in
Referring to
Next, referring to
Then, referring to
The output voltages V1, V2 can be increased to an on-voltage of the lateral IGBT of the main cell 40 or a forward voltage Vf of the lateral FWD of the main cell 42 by increasing resistances of the sense resistors Rs1, Rs2. Here, it is assumed that the lateral IGBT has a collector current-voltage characteristic shown in
As described above, according to the third embodiment, a switch of an inverter circuit for driving a three-phase motor can be formed with the lateral IGBT of the first embodiment and the lateral FWD of the second embodiment. Thus, the magnitude and current in the switch can be accurately detected.
An inverter circuit according to a fourth embodiment of the present invention is described below with reference to
The inverter circuit is formed in a SOI substrate and includes an inverter output circuit 50, a control circuit 51. The inverter output circuit 50 includes three phase legs connected in parallel to each other. A u-phase leg of the inverter output circuit 50 consists of a top switch 50a and a bottom switch 50b connected in series with the top switch 50a. A v-phase leg of the inverter output circuit 50 consists of a top switch 50c and a bottom switch 50d connected in series with the top switch 50c. A w-phase leg of the inverter output circuit 50 consists of a top switch 50e and a bottom switch 50f connected in series with the top switch 50e. The control circuit 51 controls the six switches 50a-50f.
The top switches 50a, 50c, and 50e and the bottom switches 50b, 50d, and 50f are alternately arranged in the left-to-right direction of
Detailed layouts of the switches 50a-50f are discussed below. Each of the switches 50a-50f is laid out in the same manner. In the discussion below, the top switch 50a is taken as an example. In the top switch 50a, multiple main cells 52a, each of which has an ellipse shape, are arranged side by side in the top-to-bottom direction of
In this way, each of the switches 50a-50f of the inverter circuit of the third embodiment is constructed with the lateral IGBT of the first embodiment and the lateral FWD of the second embodiment. In the switches 50a-50f, the main cells 52a-52f, the sense cells 53a-53f, the main cells 54a-54f, the sense cells 55a-55f, the sense resistors Rs1, Rs2, and the buffer circuits 56a-56f are arranged in the top-to-bottom direction, respectively. In such an approach, a chip size can reduced as much as possible. Accordingly, the length of wiring can be reduced as much as possible.
Further, the sense cells 53a-53f, the sense cells 55a-55f, the sense resistors Rs1, Rs2, and the buffer circuits 56a-56f are arranged in a line in the left-to-right direction, respectively. Thus, the chip size and the wiring length can be reduced efficiently. Preferably, the sense resistors Rs1, Rs2 can be located between the sense cells 53a-53f and the sense cells 55a-55f in the left-to-right direction.
Further, the sense cells 53a-53f, the sense cells 55a-55f, the sense resistors Rs1, Rs2, and the buffer circuits 56a-56f are located between the main cells 52a-52f and the main cells 54a-54f in the top-to-bottom direction, respectively. In such an approach, the chip size and the wiring length can be reduced efficiently.
As shown in
A first wire 64 is located in a space enclosed by the emitter wire 57, the collector wire 58, the anode wire 59, the cathode wire 60, the common negative wire 61, and the common positive wire 62. The sense cell 53a, the sense cell 55a, the sense resistors Rs1, Rs2, and the buffer circuit 56a are connected together by the first wire 64. A second wire 65 is located in the space and connects the sense resistor Rs1 to the emitter wire 57. Thus, the sense resistor Rs1 is connected to the common negative wire 61 through the second wire 65 and the emitter wire 57. A third wire 66 is located in the space and connects the sense resistor Rs2 to the anode wire 59. Thus, the sense resistor Rs2 is connected to the common negative wire 61 through the third wire 66 and the anode wire 59.
In each of the switches 50a-50f, the wiring is laid out in the above manner. Thus, the wiring length can be reduced as much as possible so that malfunction due to noise can be reduced. Specifically, the sense resistors Rs1, Rs2 can be electrically connected by the shortest path to the emitter wire 57 of each of the main cells 52a-52f and the anode wire 59 of each of the main cells 54a-54f. Thus, the noise is reduced so that the malfunction can be reduced. Further, since the sense cells 53a-53f and the sense cells 55a-55f are located between the main cells 52a-52f and the main cells 54a-54f, the emitter wire 57, the collector wire 58, the anode wire 59, and the cathode wire 60 can be connected by the shortest path through the common negative and positive wires 61, 62.
For example, when the control circuit 51 has a comparator, the comparator can be formed with only a complementary metal oxide semiconductor (CMOS). As compared to a comparator formed with a bipolar transistor, a comparator formed with a CMOS has a large offset voltage. Therefore, when the comparator of the control circuit 51 is formed with only a CMOS, the change in the polarity of the current can be accurately detected.
A fifth embodiment of the present invention is described below with reference to
Like the first embodiment, according to the first embodiment, the main cell and the sense cell are located in different islands that are electrically insulated from each other by the trench structures 1d.
Unlike the first embodiment, a sub-sense cell is located in the main cell island. In the main cell island, multiple main cells are arranged in a direction perpendicular to the longitudinal direction of the collector region 4. The sub-sense cell is formed with a straight portion of the emitter region 7 of the outermost main cell.
Specifically, as shown in
Thus, in the main cell island, the main cell is located on each side of the sub-sense cell, and the emitter of the sub-sense cell is located between the emitters of the main cell. The body layer 9 of the main cell is separated from the body layer 9 of the sub-sense cell to provide junction isolation for preventing a leak current therethrough.
Further, in the main cell island, a p+-type isolation layer 8a is formed between the emitter region 7 of the sub-sense and the emitter region 7 of the main cell. The isolation layer 8a extends from an end of the contact layer 8 toward an end of the emitter region 7 in a direction perpendicular to the longitudinal direction of the contact layer 8. The isolation layer 8a reduces or prevents operation of a parasitic transistor, which is constructed with the emitter region 7, the body layer 9, and, the drift layer 2 in each of the main cell and the sub-sense cell.
As described above, according to the fifth embodiment, the sub-sense cell is formed in the main cell island. In such an approach, the current flowing through the main cell can be detected by using not only the sense cell in the sense cell island but also the sub-sense cell in the main cell island. Thus, both the change in polarity of the current and the absolute value of the current can be accurately detected.
Specifically, the zero-crossing point of the current is detected based on an output voltage of the sense cell in the sense cell island, and the absolute value of the current is detected by the sub-sense cell in the main cell island.
There is a possibility that the absolute value of the current flowing through the main cell not accurately correspond to the output voltage of the sense cell. A reason for this is that the emitter current density in the sense cell in the sense cell island is much different from the emitter current density in the main cell. Therefore, it is difficult to accurately detect the absolute value of the current flowing through the main cell based on the output voltage of the sense cell in the sense cell island. It is noted that the change in the polarity of the current in the main cell can be easily detected by increasing the output voltage of the sense cell.
In contrast, the absolute value of the current flowing through the main cell accurately corresponds to the output voltage of the sub-sense cell in the main cell island. A reason for this is that the sub-sense cell is located in the main cell so that the emitter current density in the sub-sense cell can approach the emitter current density in the main cell. Thus, the mirror ratio almost depends on the ratio between the lengths of the emitters of the main cell and the sub-sense cell so that the absolute value of the current flowing through the main cell can accurately correspond to the output voltage of the sub-sense cell. Therefore, the absolute value of the current flowing through the main cell can be accurately detected based on the output voltage of the sub-sense cell.
In this way, according to the fifth embodiment, both the change in the polarity of the current in the main cell and the absolute value of the current in the main cell can be accurately detected. Further, since the effective area of the sub-sense cell in the main cell island can be much smaller than the effective area of the main cell, the mirror ratio can be reduced so that the current in the sub-sense cell can be reduced. Thus, a loss in the sub-sense cell can be reduced. In contrast, the effective area of the sense cell in the sense cell island cannot be much smaller than the effective area of the main cell. However, a loss in the sense cell can be reduced by increasing the resistance of the sense resistor Rs1 to limit the current in the sense cell.
A lateral IGBT according to a sixth embodiment of the present invention is described below with reference to
According to the sixth embodiment, as shown in
The SOI substrate 1 includes a supporting substrate 1a, a buried oxide (BOX) layer 1b on the supporting substrate 1a, and an active layer 1c on the buried oxide layer 1b. For example, the supporting substrate 1a can be a silicon substrate. According to the sixth embodiment, the active layer 1c serves as an n−-type drift layer 2. Each part of the lateral IGBTs of the main cell and the sense cell is formed in a surface portion of the drift layer 2.
The thickness of the BOX layer 1b, and the thickness and the impurity concentration of the active layer 1c (i.e., drift layer 2) are not limited to specific values and can vary depending on the intended use of the semiconductor device. For example, in order to achieve high breakdown voltage, it is preferable that the thickness of the BOX layer 1b be 4 micrometers (μm) or more. In order to ensure a breakdown voltage of 600V or more, it is preferable that the thickness of the BOX layer 1b be 5 μm or more. In order to ensure the breakdown voltage of 600V or more, it is preferable that the active layer 1c have the n-type impurity concentration of from 1×1014 cm−3 to 1.2×1015 cm−3, if the thickness of the active layer 1c is 15 μm or less. In order to ensure the breakdown voltage of 600V or more, it is preferable that the active layer 1c have the n-type impurity concentration of from 1×1014 cm−3 to 8×1014 cm−3, if the thickness of the active layer 1c is 20 μm.
The LOCOS oxide layer 3 is formed on a surface of the drift layer 2. The parts of the lateral IGBT are electrically insulated from each other by the LOCOS oxide layer 3. A p+-type collector region 4 is formed in the surface portion of the drift layer 2 and exposed outside the LOCOS oxide layer 3. The collector region 4 has a longitudinal direction parallel to a surface of the SOI substrate 1. The collector region 4 is surrounded by an n-type buffer layer 5. The buffer layer 5 has an impurity concentration greater than that of the drift layer 2.
A p-channel well layer 6, an n+-type emitter region 7, a p+-type contact layer 8, and a p-type body layer 9 are formed in the surface portion of the drift layer 2. The well layer 6, the emitter region 7, the contact layer 8, and the body layer 9 extend parallel to the collector region 4 and are exposed outside the LOCOS oxide layer 3.
A surface portion of the well layer 6 serves as a channel region. For example, the well layer 6 can have the thickness of 2 μm or less and the width of 6 μm or less. As shown in
The emitter region 7 is formed in a surface portion of the well layer 6 and terminated inside the well layer 6. The emitter region 7 extends in the longitudinal direction of the collector region 4. According to the sixth embodiment, as shown in
The contact layer 8 fixes the well layer 6 to an emitter potential and has an impurity concentration greater than that of the well layer 6. As shown in
The body layer 9 reduces a voltage drop caused by a Hall current flowing from a collector to an emitter. The longitudinal direction of the body layer 9 is parallel to the longitudinal direction of the collector region 4 (and the collector electrode 12). The body layer 9 reduces or prevents operation of a parasitic npn transistor, which is constructed with the emitter region 7, the well layer 6, and, the drift layer 2. Thus, turn-off time can be improved.
Assuming that the well layer 6, the emitter region 7, the contact layer 8, and the body layer 9 are considered as one set, two sets of these are arranged side by side in a width direction, perpendicular to the longitudinal direction, of the collector region 4. As shown in
A p+-type isolation layer 8a is formed between the emitter region 7 of the sub-sense and the emitter region 7 of the main cell. The isolation layer 8a extends from an end of the contact layer 8 toward an end of the emitter region 7 in a direction perpendicular to the longitudinal direction of the contact layer 8. The isolation layer 8a reduces or prevents operation of a parasitic transistor, which is constructed with the emitter region 7, the body layer 9, and, the drift layer 2 in each of the main cell and the sense cell.
A gate electrode 11 is located on a surface of the well layer 6 through a gate insulating layer 10. For example, the gate electrode 11 can be made of doped polysilicon. The surface portion of the well layer 6 becomes the channel region by applying a voltage to the gate electrode 11.
A collector electrode 12 is located on and electrically connected to the collector region 4. An emitter electrode 13 is located on and electrically connected to the emitter region 7 and the contact layer 8. As described above, according to the sixth embodiment, two sets, each of which has the well layer 6, the emitter region 7, the contact layer 8, and the body layer 9, are arranged side by side. The emitter electrode 13 of one set is located adjacent and electrically connected to the emitter electrode 13 of the other set.
As shown in
Since the collector wire 16, the main wire 15a, and the sense wire 15b do not cross each other, the effect of coupling current caused by potential variations in the collector can be reduced. Thus, accuracy with which the sense cell detects the current can be improved.
Next, operations of the lateral IGBT according to the sixth embodiment are described below. When a predetermined voltage is applied to the gate electrode 11, the channel region appears in the surface portion of the well layer 6, which is located below the gate electrode 11 between the emitter region 7 and the drift layer 2. Electrons flow from the emitter electrode 13 and the emitter region 7 into the drift layer 2 through the channel region. Accordingly, holes flow into the drift layer 2 through the collector electrode 12 and the collector region 4. Thus, conductivity modulation occurs in the drift layer 2 so that a large current can flow between the emitter and the collector. In this way, the lateral IGBT operates.
An advantage of the sixth embodiment is summarized below. According to the sixth embodiment, the main cell is located on each side of the sense cell so that the emitter of the sense cell can be located between the emitters of the main cell. Thus, the emitter current density in the main cell and the emitter current density in the sense cell approach each other so that a mirror ratio can approach a ratio between the lengths of the emitters of the main cell and the sense cell. Further, when the emitter current density in the main cell and the emitter current density in the sense cell approach each other, the amount of current per unit area during switching operation, where a large current flow, can be smaller in the sense cell than in the main cell. Thus, non-uniformity in current distribution is reduced so that the breakdown voltage can be improved.
Therefore, the sense cell can accurately detect the current flowing through the main cell with an improved linearity, even when the lateral IGBT is used as a high breakdown voltage device.
A lateral IGBT according to a seventh embodiment of the present invention is described below with reference to
Like the sixth embodiment, the collector region 4 has the longitudinal direction and is surrounded by the buffer layer 5. Unlike the sixth embodiment, the collector region 4 and the buffer layer 5 are located in the center of the well layer 6, the emitter region 7, the contact layer 8, and the body layer 9.
Specifically, as shown in
In each cell, as shown in
Further, according to the seventh embodiment, a resistor layer 14 serving as a field plate is formed on the LOCOS oxide layer 3 between the collector and the gate. For example, the resistor layer 14 can be made of doped polysilicon. The resistor layer 14 serves to maintain a uniform potential gradient between the collector and the gate. Specifically, as shown in
In and example shown in
The main cell is located on each side of the sense cell so that the emitter of the sense cell can be located between the emitters of the main cell. As shown in
Thus, like the sixth embodiment, the collector wire 16, the main wire 15a, and the sense wire 15b do not cross each other so that the effect of coupling current caused by potential variations in the collector can be reduced. Thus, accuracy with which the sense cell detects the current can be improved. Further, the wiring length can be reduced as much as possible so as to reduce noise.
Further, as shown in
The sense resistor Rs can be formed with various types of resistors. For example, the sense resistor Rs can be a diffused resistor formed in an island that is electrically isolated from the island where the main cell and the sense cell are formed. Alternatively, the sense resistor Rs can be a polisilicon or a thin-film resistor formed on an interlayer insulation layer.
Although the resistor layer 14 serving as a field plate improves the breakdown voltage, the resistor layer 14 can act as a source of noise due to the fact that the potential of the resistor layer 14 changes during switching operation. The noise may reduce the accuracy with which the current is detected. However, since the sense wire 15b extends in the direction far away from the collector not to cross the resistor layer 14, the reduction in the accuracy can be prevented even if the resistor layer 14 acts as a source of noise.
Further, according to the seventh embodiment, the sense cell is located in almost the center of the straight portion of the emitter of the main cell in the longitudinal direction. In such an approach, the amount of holes flowing into the sense cell can almost depend on the average hole concentration in the main cell. Thus, the mirror ratio approaches the ratio between the lengths of the main cell and the sense cell so that a variation in the mirror ratio can be reduced.
In the example shown in
An eighth embodiment of the present invention is described below with reference to
In such an approach, the resistance on each side of the sense cell is balanced so that operations of the main cell on each side of the sense cell can be balanced. Thus, the current can be accurately detected by the sense cell.
Likewise, the sense resistor Rs shown in
An inverter circuit according to a ninth embodiment of the present invention is described below with reference to
The inverter circuit is formed in the SOI substrate 1 and includes an inverter output circuit 70, a control circuit 71. The inverter output circuit 70 includes three phase legs connected in parallel to each other. A u-phase leg of the inverter output circuit 70 consists of a top switch 70a and a bottom switch 70b connected in series with the top switch 70a. A v-phase leg of the inverter output circuit 70 consists of a top switch 70c and a bottom switch 70d connected in series with the top switch 70c. A w-phase leg of the inverter output circuit 70 consists of a top switch 70e and a bottom switch 70f connected in series with the top switch 70e. The control circuit 71 controls the six switches 70a-70f.
The top switches 70a, 70c, and 70e and the bottom switches 70b, 70d, and 70f are alternately arranged in the left-to-right direction of
Each of the lateral IGBTs 72a-72f has main cells 75a-75f and sense cells 74a-74f. The lateral IGBTs 72a-72f are identical in structure. For example, in the lateral IGBT 72a, the main cells 75a, each of which has an ellipse shape, are arranged in the top-to-bottom direction of
As described above, according to the ninth embodiment, the sense cells 74a-74f are located in the outermost main cells 75a-75f that are located closest to the control circuit 71. In such an approach, the sense wires of the sense cells 74a-74f can be laid out not to cross the main wires of the main cells 75a-75f and anode and cathode wires of the lateral FWDs 73a-73f. That is, the sense wires of the sense cells 74a-74f can be laid out not to cross high voltage wires of the lateral IGBTs 72a-72f and the lateral FWDs 73a-73f. Therefore, even when the output voltage (i.e., voltage across the sense resistor Rs) of the sense cell is small, for example, 300 mV or less, the output voltage is not affected by the high voltage wires (e.g., up to 300V) of the lateral IGBTs 72a-72f and the lateral FWDs 73a-73f. Thus, the current can be accurately detected based on the output voltage.
Further, since the effect of reverse recovery currents in the lateral FWD 73a-73f is reduced, and the length of the wiring to the control circuit 71 is minimized, the effect of noise in the lateral IGBTs 72a-72f can be reduced.
An inverter circuit 101 according to a tenth embodiment of the present invention is described below with reference to
The inverter circuit 101 is configured to drive a three-phase motor 103. The inverter circuit 101 is integrated in the semiconductor device 102 so that the semiconductor device 102 can be configured as one-chip inverter driver IC.
As shown in
The semiconductor device 102 has an inverter output circuit 110, a control circuit 106, and a part of a bootstrap circuit 107. The inverter output circuit 110 includes three phase legs connected in parallel to each other. A u-phase leg of the inverter output circuit 110 consists of a top switch 110a and a bottom switch 110b connected in series with the top switch 110a. A v-phase leg of the inverter output circuit 110 consists of a top switch 110c and a bottom switch 110d connected in series with the top switch 110c. A w-phase leg of the inverter output circuit 110 consists of a top switch 110e and a bottom switch 110f connected in series with the top switch 110e. In
As shown in
In the semiconductor device 102, the top switches 110a, 110c, and 110e and the bottom switches 110b, 110d, and 110f are alternately arranged in a predetermined pattern. Specifically, in an example shown in
According to the tenth embodiment, as shown in
The active layer 131c is an n−-type layer and serves as a n−-type drift layer 132 in the IGBT region. Each part of the IGBT 111a-111f is formed in a surface portion of the drift layer 132. The active layer 131c serves as a n−-type cathode layer 150 in the FWD region. Each part of the FWD 112a-112f is formed in the cathode layer 150.
In the IGBT region shown in
A p+-type collector region 134 is formed in the surface portion of the drift layer 132 and exposed outside the LOCOS oxide layer 133. The collector region 134 is surrounded by a n-type buffer layer 135 having an impurity concentration greater than that of the drift layer 132. A p-channel well layer 136, an n+-type emitter region 137, a p+-type contact layer 138, and a p-type body layer 139 are formed in the surface portion of the drift layer 132 and exposed outside the LOCOS oxide layer 133. The well layer 136, the emitter region 137, the contact layer 138, and the body layer 139 are arranged around the collector region 134.
A surface portion of the well layer 136 serves as a channel region. The well layer 136 is arranged circularly around the collector region 134 (and a collector electrode 142, which is described later) so that the collector region 134 can be singly surrounded by the well layer 136. The emitter region 137 is formed in a surface portion of the well layer 136 and terminated inside the well layer 136. According to the tenth embodiment, one emitter region 137 is located on each side of the contact layer 138.
The contact layer 138 fixes the well layer 136 to an emitter potential and has an impurity concentration greater than that of the well layer 136. The body layer 139 reduces a voltage drop caused by a Hall current flowing from a collector to an emitter. Thus, the body layer 139 reduces or prevents operation of a parasitic npn transistor, which is constructed with the emitter region 137, the well layer 136, and, the drift layer 132. In such an approach, turn-off time can be improved.
A gate electrode 141 is located on a surface of the well layer 136 through a gate insulating layer 140. For example, the gate electrode 141 can be made of doped polysilicon. The surface portion of the well layer 136 becomes the channel region by applying a voltage to the gate electrode 141.
A collector electrode 142 is located on and electrically connected to the collector region 134. An emitter electroder 143 is located on and electrically connected to the emitter region 137 and the contact layer 138.
Further, a resistor layer 144 is formed on the LOCOS oxide layer 133 between the collector and the gate. For example, the resistor layer 144 can be made of doped polysilicon. The resistor layer 144 serves to maintain a uniform potential gradient between the collector and the gate. Specifically, the resistor layer 144 is wound around the collector electrode 142 to form a spiral shape. The resistor layer 144 is electrically connected at one end to the collector electrode 142 and at the other end to the gate electrode 141. The potential of the resistor layer 144 decreases with the distance from the collector electrode 142 due to a voltage drop caused by an internal resistance of the resistor layer 144. Thus, the potential gradient in the resistor layer 144 can be maintained uniform. Accordingly, the potential gradient in the drift layer 132, which is located below the resistor layer 144 across the LOCOS oxide layer 133, can be maintained uniform.
In the FWD region shown in
A cathode electrode 155 and an anode electrode 156 are formed on a surface of the SOI substrate 131. The cathode electrode 155 is electrically connected to the contact layer 151. The anode electrode 156 is electrically connected to the contact layer 154 and the anode layer 153. Further, a resistor layer 157 is formed on the LOCOS oxide layer 133 between the anode and the cathode. For example, the resistor layer 157 can be made of doped polysilicon. The resistor layer 157 serves to maintain a uniform potential gradient between the anode and the cathode. Specifically, the resistor layer 157 is wound around the cathode electrode 155 to form a spiral shape. The resistor layer 157 is electrically connected at one end to the cathode electrode 155 and at the other end to the anode electrode 156. The potential of the resistor layer 157 decreases with the distance from the cathode electrode 155 due to a voltage drop caused by an internal resistance of the resistor layer 157. Thus, the potential gradient in the resistor layer 157 can be maintained uniform. Accordingly, the potential gradient in the active layer 131c, which is located below the resistor layer 157 across the LOCOS oxide layer 133, can be maintained uniform.
The control circuit 106 drives the u-phase leg, the v-phase leg, and the w-phase leg of the inverter output circuit 110, thereby controlling the three-phase motor 103. For the sake of simplicity, in
The gate drivers 113a, 113c, and 113e drive the top switches 110a, 110c, and 110e, respectively. The gate drivers 113b, 113d, and 113f drive the bottom switches 110b, 110d, and 110f, respectively. The gate drivers 113a-113f output the gate voltages to the gates of the IGBTs 111a-111f, respectively, so that the IGBTs 111a-111f can be driven according to the gate voltages. The gate voltages are controlled by the microcomputer 105.
The IGBTs 111a, 111c, and 111e, which are driven by the gate drivers 113a, 113c, and 113e, operate with reference to a high potential. In contrast, the IGBTs 111b, 111d, and 111f, which are driven by the gate drivers 113b, 113d, and 113f, operate with reference to a low potential. Therefore, there is a need to shift a level of the reference potential. The first level shifter 114a is located between the top switch 110a and the bottom switch 110b. The second level shifter 114b is located between the top switch 110c and the bottom switch 110d. The third level shifter 114c is located between the top switch 110e and the bottom switch 110f.
The power supply circuit 115a-115f generate power supply voltages based on which the gate drivers 113a-113f operate.
The protection circuits 116a-116f detect the voltage of the main power source 104 and control the gate voltages, outputted from the gate drivers 113a-113f, based on the detected voltage of the main power source 104. For example, when the voltage of the main power source 104 is reduced below a predetermined threshold, the gate voltages are controlled so that the IGBTs 111a-111f can be turned OFF. In such an approach, the inverter circuit 101 and the three-phase motor 103 can be protected from malfunction.
Further, the protection circuits 116a-116f can detect an overheat condition of the semiconductor device 102. For example, the overheat condition can be detected based on a diode forward voltage Vf, which changes depending on a temperature. When the overheat condition is detected, the gate voltages are controlled so that the IGBTs 111a-111f can be turned OFF. In such an approach, the inverter circuit 101 and the three-phase motor 103 can be protected from malfunction.
The logic circuits 117a-117c receive commands from the microcomputer 105. The commands are used to drive the switches 110a-110f. The logic circuits 117a-117c output gate control signals to the gate drivers 113a-113f according to the commands. The gate drivers 113a-113f outputs the gate voltages according to the gate control signals.
The bootstrap circuit 107 generates a floating power supply from a voltage Vcc that is generated by an external power supply converter 108. The bootstrap circuit 107 includes diodes 107a-107c, resistors 107d-107f, and capacitors 107g-107i. The diode 107a, the resistor 107d, and the capacitor 107g form a first bootstrap circuit for the u-phase. The diode 107b, the resistor 107e, and the capacitor 107h form a second bootstrap circuit for the v-phase. The diode 107c, the resistor 107f, and the capacitor 107i form a third bootstrap circuit for the w-phase. In an initial state, the IGBTs 111b, 111d, and 111f are turned ON so that the capacitors 107g-107i can be charged through the diodes 107a-107c and the resistors 107d-107f. Thus, the floating power supplies can be generated by the capacitors 107g-107i. According to the tenth embodiment, the diodes 107a-107c and the resistors 107d-107f are integrated in the semiconductor device 102.
In this way, the IGBTs 111a-111f, the FWDs 112a-112f, the control circuit 106, and the part of the bootstrap circuit 107 are integrated in the SOI substrate 131 to form the semiconductor device 102 as one-chip inverter driver IC. Thus, the semiconductor device 102 can be reduced in size. Further, wire lengths can be reduced so that parasitic components such as parasitic inductance and parasitic resistance can be reduced.
Although not shown in
The current detection circuit is configured to detect the magnitude and direction of current flowing through the bottom switch 110b. Further, the circuit detection circuit detects an overcurrent condition in the bottom switch 110b. The detection result of the current detection circuit is sent to the microcomputer 105, and the gate voltages outputted from the gate drivers 113a-113f are controlled according to the detection result. For example, when the overcurrent condition is detected, the IGBTs 111a-111f can be turned OFF to protect the inverter circuit 101 and the three-phase motor 103 from malfunction.
Specifically, the current detection circuit includes a sense IGBT 111bs and a sense FWD 112bs. The IGBT 111b and the FWD 112b are hereinafter called the “main cell”, and the sense IGBT 111bs and the sense FWD 112bs are hereinafter called the “sense cell”. An area of the sense cell is 1/N of an area of the main cell. A current flowing through the sense cell becomes smaller than a current flowing through the main cell depending on the area ratio.
As shown in
A method of detecting the magnitude and direction of the current flowing through the bottom switch 110b is described below with reference to
When the IGBT 111b is turned ON, the current flows from the collector to the emitter of the IGBT 111b, as shown in
Then, when the IGBT 111b is turned OFF from ON, a reverse recovery current flows through the FWD 112b, as shown in
Then, the recovery current becomes zero after a lapse of a certain period of time. As a result, no current flows through the IGBT 111b and the FWD 112b, as shown in
As shown in
Then, as shown in
Then, as shown in
As described above, according to the tenth embodiment, the sense cell as a current detection circuit is provided to only the bottom switches 110b, 110d, and 110f. The sense resistor Rs1 is connected in series with the sense cell of the lateral IGBT, and the sense resistor Rs2 is connected in series with the sense cell of the lateral FWD. Therefore, the absolute value and direction of the current in each phase can be detected by the voltage V1 across the sense resistor Rs1 and the voltage V2 across the sense resistor Rs2.
Thus, sensorless sinusoidal control of the current in each phase can be achieved so that the three-phase motor 103 can be driven with a low noise level. Since there is no need to use additional current sensor such as a Hall effect sensor, the inverter circuit 101 can be reduced in size and simplified in structure. Accordingly, the manufacturing cost of the inverter circuit 101 can be reduced.
Further, according to the tenth embodiment, the parts of the inverter circuit 101 are integrated in a common semiconductor substrate (i.e., SOI substrate 131) to form a single chip semiconductor device 102. Thus, the size can be reduced, and the wring length can be reduced. The reduction in the wiring length can reduce parasitic components such as parasitic capacitances and parasitic inductances. Therefore, the current can be detected accurately.
Further, according to the tenth embodiment, when the overcurrent condition is detected, the IGBTs 111a-111f can be turned OFF to protect the inverter circuit 101 and the three-phase motor 103 from malfunction. Likewise, when the overheat condition is detected, the gate voltages are controlled so that the IGBTs 111a-111f can be turned OFF to protect the inverter circuit 101 and the three-phase motor 103 from malfunction. In such an approach, the inverter circuit 1 and the three-phase motor 103 can be surely protected from malfunction.
An eleventh embodiment of the present invention is described below.
In the inverter circuit 101 according to the tenth embodiment, when an induced voltage produced by operation of the inverter output circuit 110 is in phase with a motor current supplied to the three-phase motor 103, power supplied to the three-phase motor 103 is maximized.
Specifically, the phases of the induced voltage and the motor current can be detected in the following ways.
Regarding the phase of the motor current, a zero-crossing occurs when the polarity of the current detected by the current detection circuit changes. Therefore, when the zero-crossing occurs, it can be determined that the phase of the motor current is 0°, 180°, or 360°.
The phase of the induced voltage can be detected based on the change in the motor current. Specifically, an equation about the induced voltage is given as follows: ω·φmax·sin θ+L·dI/dt=0, where θ is a phase of the induced voltage, ω is an angular velocity, L is an inductance, φmax is an interlinkage magnetic flux, and dI/dt is a change in the motor current. The change in the motor current is discussed in detail below with reference to
The ON and OFF operation of the IGBTs 111a-111f is controlled by pulse width modulation (PWM) technique. In this case, the change in the motor current is not uniform due to the ON and OFF operation of the IGBTs 111a-111f. Specifically, as shown n
In this way, the phase of the motor current can be detected based on the polarity of the motor current. Further, the phase of the induced voltage can be detected based on the change in the motor current by a known technique, for example, as disclosed in JP 4396762.
However, as mentioned above, the change in the motor current is not uniform due to the ON and OFF operation of the IGBTs 111a-111f. Therefore, there is a possibility that the phase of the induced voltage is not accurately detected, if the motor current is detected at the timing of switching of the IGBTs 111a-111f. To prevent this problem, according to the eleventh embodiment, the motor current is detected in accordance with a timing chart shown in
The triangle wave signal is used as a reference threshold of the PWM control. The polarity detection timing signal is outputted from the microcomputer 105 according to a change between a peak and a trough of the triangle wave signal. The current sampling pulse determines a detection timing of the motor current. According to the eleventh embodiment, the motor current is detected when the current sampling pulse becomes a high level. The gradient detection timing signal is outputted from the microcomputer 105 and used to generate the first and second sampling pulses. The first and second sampling pulses determine a detection timing of the change in the motor current. The first sampling pulse is outputted at a rising edge of the gradient detection timing signal, and the second sampling pulse is outputted at a falling edge of the gradient detection timing signal. A first value of the motor current is held in response to the first sampling pulse, and a second value of the motor current is held in response to the second sampling pulse. Then, the first value is compared with the second value to detect the change in the motor current during a period from when the first sampling pulse is outputted to when the second sampling pulse is outputted. The current sampling pulse, the first sampling pulse, and the second sampling pulse are generated by an external logic circuit (not shown) based on the polarity detection timing signal and the gradient detection timing signal that are outputted from the microcomputer 105. The timing at which the current sampling pulse becomes a high level corresponds to a first determination timing in claims. The timing at which the first and second sampling pulses become a high level corresponds to a second determination timing in claims.
As shown in
For the above reasons, according to the eleventh embodiment, the motor current and the change in the motor current are detected within a period when all the IGBTs 111b, 111d, and 111f are ON.
Specifically, the current sampling pulse becomes a high level at a falling edge of the polarity detection timing signal. In other words, the current sampling pulse becomes a high level at the trough of the triangle wave signal. The motor current is detected when the current sampling pulse becomes a high level.
As can be seen from
As shown in
The current detector 210 outputs a current detection signal corresponding to the voltages V1, V2. The multiplexer 220 selects one of the current detection signals of the three phases and outputs the selected current detection signal. The selected current detection signal is amplified by the amplifier and then inputted to each of the current polarity detector 240 and the induced voltage polarity detector 250.
The current polarity detector 240 detects the polarity of the motor current based on the amplified selected current detection signal. For example, the current polarity detector 240 detects the polarity of the motor current by comparing a voltage indicated by the amplified selected current detection signal with a reference voltage. The current polarity detector 240 generates a first signal depending on the detected polarity of the motor current and outputs the first signal to the latch 260. For example, when the detected polarity of the motor current is a positive, the first signal can be a high level signal, and when the detected polarity of the motor current is a negative, the first signal can be a low level signal.
The induced voltage polarity detector 250 detects the polarity of the induced voltage based on the amplified selected current detection signal. For example, the induced voltage polarity detector 250 can include a capacitor and a comparator. The capacitor starts to be charged based on the amplified selected current detection signal, when the first sampling pulse is outputted. The comparator compares a voltage of the charged capacitor with a voltage indicated by the amplified selected current detection signal. The induced voltage polarity detector 250 detects the polarity of the induced voltage based on whether the voltage of the charged capacitor is greater than the voltage indicated by the amplified selected current detection signal. Then, the induced voltage polarity detector 250 generates a second signal depending on the detected polarity of the induced voltage and outputs the second signal to the latch 260. For example, when the detected polarity of the induced voltage is a positive, the second signal can be a high level signal, and when the detected polarity of the induced voltage is a negative, the second signal can be a low level signal.
The latch 260 holds the first signal outputted from the current polarity detector 240 and outputs the first signal to the microcomputer 105. Likewise, the latch 260 holds the second signal outputted from the induced voltage polarity detector 250 and outputs the second signal to the microcomputer 105. According to the eleventh embodiment, the latch 260 includes two D-latch circuits. One D-latch circuit holds the first signal in response to the current sampling pulse. The other D-latch circuit holds the second signal in response to the second sampling pulse. Thus, the latch 260 outputs the first signal to the microcomputer 105 when the current sampling pulse becomes a high level, and outputs the second signal to the microcomputer 105 when the second sampling pulse becomes a high level. Therefore, the first signal inputted to the microcomputer 105 indicates the polarity of the motor current at the rising edge of the current sampling pulse, i.e., at the peak of the triangle wave signal. The second signal inputted to the microcomputer 105 indicates the result of comparison between the voltage of the capacitor charged during the high level period of the first sampling pulse and the voltage indicated by the amplified selected current detection signal at the rising edge of the second sampling pulse.
In this way, the first signal indicative of the polarity of the motor current and the second signal indicative of the polarity of the induced voltage are inputted to the microcomputer 105. In the microcomputer 105, the commands for PWM controlling the IGBTs 111a-111f are adjusted based on the first signal and the second signal so that the motor current and the induced voltage can be in phase with each other. In such an approach, the power supplied to the three-phase motor 103 can be maximize.
In the phase detection circuit 200, a constant voltage (e.g., 5V), which is used as a reference voltage for the amplifier circuit 230, is generated from the voltage Vcc (e.g., 15V) that is generated by the power supply converter 8. The voltage Vcc is generated by stepping down the high voltage supplied from the main power source 104. Specifically, the power supply converter 108 has a power semiconductor element (i.e., power MOSFET 320 shown in
The power supply converter 108 is a DC-DC converter and generates the voltage Vcc from the high voltage (e.g., 288V) supplied from the main power source 104. Specifically, as shown in
The IPD 120 performs control for generating a stable voltage Vcc (e.g., 15V) from the high voltage. As described in detail later, a semiconductor power element incorporated in the IPD 120 is turned ON and OFF to stabilize the voltage Vcc. According to the eleventh embodiment, the IPD 120 has a power MOSFET 320 as the semiconductor power element. When the power supply converter 108 is activated, a drain of the power MOSFET 320 is connected to the main power source 104, and a source of the power MOSFET 320 is connected to the reference voltage generator 121. The IPD 120 has a D-terminal, a S-terminal, and a C-terminal. The D-terminal is connected to the drain of the power MOSFET 320 and serves as a power supply terminal. The S-terminal is connected to the source of the power MOSFET 320 and serves as an output terminal. The C-terminal is connected to the monitor voltage generator 123 so that a monitor voltage generated by the monitor voltage generator 123 can be inputted to the IPD 120. In the IPD 120, the power MOSFET 320 is controlled based on the monitor voltage so that the voltage Vcc can be stabilized. That is, the C-terminal serves as a control terminal for controlling the voltage Vcc.
The reference voltage generator 121 includes a capacitor 121a. The capacitor 121a is connected to a power supply line 108a that is connected to the S-terminal. When the IPD 120 is activated, the capacitor 121a is charged to generate a reference voltage. The reference voltage is used as a reference for the monitor voltage. Further, the reference voltage is used as a power supply voltage for the IPD 120.
The smoothing circuit 122 is configured as a LC circuit including a inductor 122a and a capacitor 122b. The inductor 122a is connected in series with the power supply line 108a. The capacitor 122b is connected in parallel with the power supply line 108a. The smoothing circuit 122 smoothes a voltage of the power supply line 108a to prevent the voltage of the power supply line 108a from varying due to noise. Further, the capacitor 122b is charged to generate the voltage Vcc. A rectifier diode 125 is connected between a high-voltage side of the inductor 122a and a ground (GND) line.
The monitor voltage generator 123 includes a Zener diode 123a and a diode 123b. The monitor voltage generator 123 generates the monitor voltage appearing at the C-terminal of the IPD 120. The monitor voltage depends on the voltage Vcc. Specifically, the monitor voltage is calculated by subtracting a voltage across the Zener diode 123a and a forward voltage Vf of the diode 123b from the voltage Vcc. For example, the monitor voltage can be 6.2V. The IPD 120 determines, based on the monitor voltage, whether the voltage Vcc is a predetermined voltage (e.g., 15V). The power MOSFET 320 is turned ON and OFF based on a result of the determination. In an example shown in
In this way, the IPD 120 is configured as a DC-DC converter for generating a stable voltage Vcc from the high voltage supplied from the main power source 104.
Next, the IPD 120 is discussed in detail below. The IPD 120 includes an activation circuit 310, the power MOSFET 320, and a PWM chopper circuit 330.
The activation circuit 310 activates the IPD 120 by generating a predetermined voltage from the high voltage that is applied by the main power source 104 to the D-terminal. Specifically, the activation circuit 310 charges the capacitor 121a of the reference voltage generator 121 based on current supply from an incorporated constant current source, thereby generating the reference voltage. It is noted that the capacitor 121a is connected between the C-terminal and the S-terminal of the IPD 120. When the reference voltage reaches a predetermined value, the current supply from the constant current source is stopped. Thus, the reference voltage having the predetermined value remains applied to the C-terminal and used as an internal power supply voltage VCS for each part of the IPD 120.
The power MOSFET 320 is turned ON and OFF by the PWM chopper circuit 330. Specifically, a gate voltage of the power MOSFET 320 is controlled by the PWM chopper circuit 330 to control an output current of the power MOSFET 320 flowing though the S-terminal. Thus, the voltage Vcc is controlled to a predetermined voltage (e.g., 15V).
The PWM chopper circuit 330 converts the voltage Vcc into a constant voltage by adjusting a pulse width (i.e., duty ratio) of PWM control for the power MOSFET 220. Specifically, the pulse width is adjusted so that the monitor voltage inputted to the C-terminal connected to the PWM chopper circuit 330 can become a predetermined voltage (e.g., 6.2V). For example, the pulse width can be determined by a well-known technique such as detecting a peak of a current flowing through the inductor 122a.
Specifically, the PWM chopper circuit 330 includes an oscillator 331, an overcurrent protection circuit 332, a logic circuit 333, an overheat protection circuit 334, and a switching stop circuit 335.
The oscillator 331 outputs a pulse signal having a predetermined period depending on a period of the PWM control. The pulse signal outputted from the oscillator 331 is used as a set signal for a SR latch 333a, which is described later. When the PWM control is performed, the power MOSFET 320 is turned ON and OFF with the period of the pulse signal outputted from the oscillator 331.
The overcurrent protection circuit 332 turns OFF the power MOSFET 320, when the output current of the power MOSFET 320 exceeds an overcurrent threshold. According to the eleventh embodiment, the overcurrent protection circuit 332 sets the overcurrent threshold based on the reference voltage inputted to the C-terminal. The overcurrent protection circuit 332 determines that an overcurrent condition occurs, when the output current of the power MOSFET 320 exceeds the overcurrent threshold.
The logic circuit 333 outputs a gate control signal for controlling the gate voltage applied to the gate of the power MOSFET 320 based on logic levels of outputs of the oscillator 331, the overcurrent protection circuit 332, the overheat protection circuit 334, and the switching stop circuit 335.
The overheat protection circuit 334 turns OFF the power MOSFET 320, when an overheat condition is detected. Further, when the overheat condition is removed, the overheat protection circuit 334 allows the power MOSFET 320 to be PWM controlled. According to the eleventh embodiment, when the overheat condition is detected, the overheat protection circuit 334 outputs a low level signal to turn OFF the power MOSFET 320.
The switching stop circuit 335 outputs a switching stop signal for stopping the switching of the power MOSFET 320 in response to a stop command from the microcomputer 105. As mentioned previously, the current polarity detection and the induced voltage polarity detection performed by the phase detection circuit 100 may result in inaccurate results, if the power MOSFET 320 of the power supply converter 108 is switched at the timings of the current polarity detection and the induced voltage polarity detection. To prevent this problem, when the current sampling pulse, the first sampling pulse, and the second sampling pulse are outputted, the microcomputer 105 outputs the stop command to the switching stop circuit 335 so that the switching stop circuit 335 can output the switching stop signal. Specifically, according to the eleventh embodiment, when the output signal of the switching stop circuit 335 becomes a low level, the switching of the power MOSFET 320 is stopped. The switching stop circuit 335 includes a level shifter 335a. The output signal of the switching stop circuit 335 is level-shifted to a reference potential of the source of the power MOSFET 320 and then inputted to the IPD 120.
In the IPD 120, the reference voltage inputted to the C-terminal is divided by resistors 332a and 332b, and the divided reference voltage is converted by an error amplifier 332c into an error amp-side voltage that depends on the reference voltage. Specifically, the divided reference voltage is inputted to an inverting input terminal of the error amplifier 332c. Therefore, the error amp-side voltage increases with a decrease in the divided reference voltage. The error amp-side voltage is inputted to a non-inverting input terminal of a comparator 332d.
A voltage (hereinafter called the “power MOSFET-side voltage”) inputted to an inverting input of the comparator 332d changes with a current flowing through the power MOSFET 320. A constant current generated by a constant current source 332e flows through a resistor 332f so that a voltage can occur across the resistor 332f. The power MOSFET-side voltage basically depends on the voltage across the resistor 332f. A power MOSFET 332g is configured as a sense cell for the power MOSFET 320 so that a current flowing though the power MOSFET 332g can be proportional to the current flowing through the power MOSFET 320. Further, the current flowing through the power MOSFET 332g flows through the resistor 332f. Therefore, the power MOSFET-side voltage changes according to the ON and OFF operation of the MOSFET 332g, i.e., the ON and OFF operation of the power MOSFET 320.
The comparator 332d compares the error amp-side voltage with the power MOSFET-side voltage. If the error amp-side voltage is greater than the power MOSFET-side voltage, the comparator 332d outputs a high level signal. In contrast, if the error amp-side voltage is smaller than the power MOSFET-side voltage, the comparator 332d outputs a low level signal. Therefore, when the output signal of the comparator 332d becomes a high level, it is detected that the overcurrent condition occurs.
It is noted that the output signal of the comparator 332d is used as a reset signal for the SR latch 333a. When the power MOSFET-side voltage becomes greater than the error amp-side voltage, the SR latch 333a is reset so that the voltage Vcc can have a predetermined value (e.g., 15V).
Then, output signals of the SR latch 333a, the overheat protection circuit 334, and the switching stop circuit 335 are inputted to an NAND gate 333b.
In normal conditions, the output signals of the overheat protection circuit 334 and the switching stop circuit 335 are high. Therefore, an output signal of the NAND gate 333b depends on the output signal of the SR latch 333a. The output signal of the NAND gate 333b is reversed by a NOT gate 333c as a driver circuit and then applied to the gate of the power MOSFET 320. Thus, the power MOSFET 320 is turned ON and OFF according to the output signal of the SR latch 333a.
In contrast, if at least one of the output signals of the overheat protection circuit 234 and the switching stop circuit 335 becomes a low level, the output signal of the NAND gate 333b becomes a high level regardless of whether the output signal of the SR latch 333a is high or low. Therefore, the output signal of the driver circuit 333c becomes a low level so that the power MOSFET 320 can be turned OFF. Thus, the power MOSFET 320 is turned OFF regardless of whether the output signal of the SR latch 333a is high or low.
Operations of the power supply converter 108 are discussed in detail below with reference to
The power supply converter 108 operates in the normal conditions as follows. At a time T1 where the pulse signal of the oscillator 331 becomes high, the output signal of the comparator 332d is low, because the power MOSFET-side voltage is less than the error amp-side voltage. Therefore, the output signal of the NAND gate 333b becomes low according to the output signal of the SR latch 333a, unless the overheat condition is detected by the overheat protection circuit 334. As a result, the output signal of the driver circuit 333c becomes high so that the power MOSFET 320 can be turned ON. Thus, the output current of the power MOSFET 200 increases so that the power MOSFET-side voltage can increase.
Then, at a time T2 where the power MOSFET-side voltage reaches the error amp-side voltage, the output signal of the comparator 332d becomes high. As a result, the SR latch 333a is reset so that the output signal of the SR latch 333a can become low. In this way, the power MOSFET 320 remains ON during the high period of the output signal of the SR latch 333a.
Then, during a time period T3 where the switching stop circuit 335 outputs the switching stop signal in response to the stop command from the microcomputer 105, the output signal of the NAND gate 333b remains low regardless of the output level of the SR latch 333a. As a result, the power MOSFET 320 is kept OFF during the time period T3. In this way, the switching operation of the power MOSFET 320 is stopped by the switching stop signal so as to prevent the power MOSFET 320 from being switched when the polarity of the current and the polarity of the induced voltage are detected.
It is noted that the stopping of the switching operation of the power MOSFET 320 results in a decrease in the voltage Vcc. The voltage of the C-terminal decreases with the decrease in the voltage Vcc so that the error amp-side voltage can increase. Therefore, a period necessary for the power MOSFET-side voltage to reach the error amp-side voltage after an elapse of the period T3 is increased. Accordingly, when the power MOSFET 320 is turned ON after the elapse of the period T3, the power MOSFET 320 is kept ON for an increased time period. Thus, the amount of the decrease in the voltage Vcc is cancelled so that the predetermined voltage can become the average of the voltage Vcc. Therefore, the stopping of the switching of the power MOSFET 320 does not cause new problem.
As described above, according to the eleventh embodiment, the IGBTs 111a-111f are PWM controlled so that the motor current and the induced voltage can be in phase with each other. In such an approach, the power supplied to the three-phase motor 103 can be maximized. Further, the switching of the power MOSFET 320 of the power supply converter 108 is stopped at the timings of the current polarity detection and the induced voltage polarity detection. In such an approach, the current polarity detection and the induced voltage polarity detection are not affected by the switching surge of the power MOSFET 320. Thus, the current polarity detection and the induced voltage polarity detection can be accurately performed.
(Modifications)
The above embodiments can be modified in various ways, for example, as follows.
The SOI substrates 1, 21 can be replaced with another type of substrate such as a simple semiconductor substrate. The structures of the lateral IGBT and the lateral FWD can vary. For example, the resistor layers 14, 30 can be omitted. The other end of the resistor layer 14 can be connected to the emitter electrode 13 instead of the gate electrode 11. The trench structures 1d, 21d can be replaced with another type of isolation structure.
In the embodiments, the lateral IGBT is of n-channel type. Alternatively, the lateral IGBT can be of p-channel type by inverting conductivity types of components (e.g., drift layer 2) of the lateral IGBT.
The semiconductor device can have another type of lateral semiconductor element such as a lateral power MOSFET in addition to or instead of the lateral IGBT and the lateral FWD.
In the embodiments, the sense cell and the sense resistor are provided to the bottom switches. Alternatively, the sense cell and the sense resistor can be provided to the top switches.
In is noted that when the sense cell and the sense resistor are provided to the top switches, a reference ground is needed to detect the current. Therefore, it is preferable that the sense cell and the sense resistor should be provided to the bottom switches.
In the embodiments, the sense resistor is connected to the low side of the sense cell. Alternatively, the sense resistor can be connected to the high side of the sense cell.
In the embodiments, the IGBTs 111a-111f are of lateral type and used as power elements. Alternatively, the IGBTs 111a-111f can be replaced with another type of power element such as a lateral or vertical power MOSFET.
In the embodiments, the inverter circuit 101 is taken as an example. The present invention can be applied to another type of circuit.
The eleventh embodiment can be combined with any of the other embodiments.
In the embodiments, the polarity of the motor current (i.e., phase of the motor current) and the polarity of the induced voltage (i.e., phase of the induced voltage) are detected based on the motor current and the change in the motor current in each phase. Alternatively, the polarity of the motor current and the polarity of the induced voltage can be detected based on a line-to-line current, which is a difference between line currents of two phases of the three phases.
In the embodiments, the microcomputer 105 and the power supply converter 108 are not integrated with the semiconductor device 102. Alternatively, the microcomputer 105 and the power supply converter 108 can be at least partially integrated with the semiconductor device 102 to form a single chip semiconductor device 102.
Such changes and modifications are to be understood as being within the scope of the present invention as defined by the appended claims.