JP2020061912A - Gate voltage control circuit - Google Patents

Abstract

To provide a gate voltage control circuit capable of improving a trade-off relationship existing between a switching loss of a main switching element and a surge voltage without adopting a complicated circuit configuration.SOLUTION: When a main switching element is turned off, a control unit of a gate voltage control circuit is configured to control ON/OFF of an ON switching element and an OFF switching element such that the ON switching element is turned off after the ON switching element and the OFF switching element have been turned on at the same time.SELECTED DRAWING: Figure 2

Description

  The technique disclosed in this specification relates to a gate voltage control circuit.

  A power conversion device such as an inverter is composed of a plurality of main switching elements, and is configured to perform power conversion by controlling switching of these main switching elements. A gate voltage control circuit that controls the gate voltage is connected to each of the plurality of main switching elements.

  The gate voltage control circuit has an on-path circuit and an off-path circuit connected in series between a first terminal to which a gate-on voltage is applied and a second terminal to which a gate-off voltage is applied. The connection point of the on-path circuit and the off-path circuit is connected to the gate of the main switching element. The on-path circuit has an on-switching element and an on-path resistance element connected in series. The off-path circuit also has an off-switching element and an off-path resistance element that are connected in series.

  The gate voltage control circuit raises the gate voltage of the main switching element to the gate-on voltage by turning on the switching element for turning on and turning off the switching element for turning off when turning on the main switching element. On the other hand, when turning off the main switching element, the gate voltage control circuit turns off the on switching element and turns on the off switching element, thereby lowering the gate voltage of the main switching element to the gate off voltage. In this way, the gate voltage control circuit can control the gate voltage of the main switching element by controlling the switching of the ON switching element and the OFF switching element.

  When the main switching element is turned off, if the gate voltage of the main switching element is dropped at a high speed, the switching loss of the main switching element can be reduced, but the surge voltage increases. On the other hand, when the main switching element is turned off, if the gate voltage of the main switching element is lowered at a low speed, the surge voltage can be suppressed from increasing, but the switching loss of the main switching element increases. Thus, when the main switching element is turned off, there is a trade-off relationship between the switching loss of the main switching element and the surge voltage.

  Patent Document 1 discloses a technique in which, when the main switching element is turned off, the gate voltage of the main switching element is lowered to the gate-off voltage after being set to a predetermined voltage. In this way, by performing the two-step control in which the gate voltage of the main switching device is once set to a predetermined voltage and then dropped to the gate-off voltage, the current change rate immediately after turn-off is suppressed to suppress the surge voltage increase and the current during the turn-off is suppressed. The rate of change can be increased and turn-off loss can be reduced.

JP, 2016-158361, A

  However, the technique of Patent Document 1 uses an error amplifier circuit to generate a predetermined voltage when turning off the main switching element, and the circuit configuration is complicated. The present specification provides a gate voltage control circuit capable of improving the trade-off relationship existing between the switching loss of the main switching element and the surge voltage without adopting a complicated circuit configuration.

  The gate voltage control circuit disclosed in this specification is a gate voltage control circuit that controls the gate voltage of a main switching element, and has a first terminal to which a gate-on voltage is applied and a second terminal to which a gate-off voltage is applied. An on-path circuit, an off-path circuit, and a controller can be provided. The on-path circuit and the off-path circuit are connected in series between the first terminal and the second terminal. A connection point between the on-path circuit and the off-path circuit is connected to the gate of the main switching element. The on-path circuit may include an on-switching element and an on-path resistance element connected in series. The ON switching element may be connected to the first terminal side of the ON path resistance element, or the ON path resistance element may be connected to the first terminal side of the ON switching element. Good. The off-path circuit may include an off-switching element and an off-path resistance element that are connected in series. The off switching element may be connected to the second terminal side of the off path resistance element, or the off path resistance element may be connected to the second terminal side of the off switching element. Good. When the control section turns off the main switching element, the on switching element and the on switching element are turned off so that the on switching element and the off switching element are turned on at the same time. It is configured to control ON / OFF of the OFF switching element. The timing for turning off the on switching element after turning on the on switching element and the off switching element at the same time is not particularly limited. For example, the on switching element may be turned off when the gate voltage of the main switching element reaches a threshold voltage after the on switching element and the off switching element are turned on at the same time. The threshold voltage is not limited to a fixed voltage and may be an adjustable voltage.

  When turning off the main switching element, the gate voltage control circuit simultaneously turns on both the on switching element and the off switching element. Accordingly, the gate voltage of the main switching element is adjusted to a voltage obtained by dividing the difference voltage between the gate on voltage and the gate off voltage by the on path resistance element and the off path resistance element. After that, the gate voltage control circuit turns off the on-switching element to lower the gate voltage of the main switching element to the gate-off voltage. As described above, the gate voltage control circuit can perform two-step control when turning off the main switching element, and thus the trade-off relationship existing between the switching loss of the main switching element and the surge voltage can be obtained. Can be improved. Further, in the above gate voltage control circuit, a circuit included in the conventional gate voltage control circuit is used as a circuit for adjusting the voltage applied to the gate of the main switching element immediately after turn-off. That is, the gate voltage control circuit uses the on-path resistance element and the off-path resistance element included in the conventional gate voltage control circuit as a voltage dividing circuit to control the voltage applied to the gate of the main switching element immediately after turn-off. Can be adjusted. As described above, the gate voltage control circuit can improve the trade-off relationship existing between the switching loss of the main switching element and the surge voltage without adopting a complicated circuit configuration.

The circuit diagram of an inverter circuit is shown. 3 shows a circuit diagram of an embodiment of a gate voltage control circuit. FIG. 7 shows a timing chart when two-step control is executed based on a comparison signal from a comparison circuit. The timing chart at the time of performing two-step control based on the timer signal from a timer is shown. The circuit diagram of other one Embodiment of a gate voltage control circuit is shown.

  As shown in FIG. 1, the inverter circuit 10 is configured to supply an alternating current to the motor 92. The inverter circuit 10 has a high voltage wiring 12 and a low voltage wiring 14. The high voltage wiring 12 and the low voltage wiring 14 are connected to a DC power source (not shown). The high voltage V + is applied to the high voltage wiring 12, and the low voltage V− is applied to the low voltage wiring 14. Three series circuits 15 are connected in parallel between the high voltage wiring 12 and the low voltage wiring 14. Each series circuit 15 has two n-type channel MOSFETs 16 connected in series between the high voltage wiring 12 and the low voltage wiring 14. The gate of each MOSFET 16 is connected to the gate voltage control circuit 20. Output wirings 11a to 11c are connected to the respective connection wirings 13 between the two MOSFETs 16 connected in series. The other ends of the output wirings 11a to 11c are connected to the motor 92. The MOSFET 16 is an example of a main switching element.

  Each gate voltage control circuit 20 is configured to control the gate voltage of the MOSFET 16 and switch the MOSFET 16. The inverter circuit 10 supplies three-phase alternating current to the motor 92 by switching each MOSFET 16.

  FIG. 2 shows a circuit diagram of the gate voltage control circuit 20. Each of the gate voltage control circuits 20 of FIG. 1 has the configuration shown in FIG. The gate voltage control circuit 20 includes a control unit 22, an on-path circuit 24, an off-path circuit 26, a timer 28, a first OR circuit OR1, a second OR circuit OR2, a comparison circuit COM1 and a reference power supply V10.

  The on-path circuit 24 and the off-path circuit 26 are connected in series between the first terminal T1 and the second terminal T2. The gate-on voltage V1 is applied to the first terminal T1. The gate-off voltage V2 is applied to the second terminal T2. The gate-on voltage V1 is a voltage that is more positive than the gate-off voltage V2. A connection point P1 between the on-path circuit 24 and the off-path circuit 26 is connected to the gate of the MOSFET 16.

  The on-path circuit 24 has an on-switch element SW1 and an on-path resistance element R1 which are P-type channel MOSFETs connected in series. The source of the ON switching element SW1 is connected to the first terminal T1, the drain of the ON switching element SW1 is connected to one end of the ON path resistance element R1, and the other end of the ON path resistance element R1 is a connection point. It is connected to P1. The gate of the ON switching element SW1 is connected to the control unit 22. The on-path resistance element R1 may be connected to the first terminal T1 side of the on-switching element SW1.

  The off-path circuit 26 includes an off-switching element SW2, which is an n-type channel MOSFET, and an off-path resistance element R2 that are connected in series. One end of the off-path resistance element R2 is connected to the connection point P1, the other end of the off-path resistance element R2 is connected to the drain of the off switching element SW2, and the source of the off switching element SW2 is the second terminal. It is connected to T2. The gate of the switching element SW2 for turning off is connected to the control unit 22. The off-path resistance element R2 may be connected to the second terminal T2 side of the off switching element SW2.

  The control unit 22 is configured by an IC or the like, and turns on / off the ON switching element SW1 of the ON path circuit 24 and the OFF switching element SW2 of the OFF path circuit 26 based on a signal from an ECU (Electronic Control Unit) not shown. Is configured to control. In this example, the ON command signal, the OFF command signal, the short circuit detection signal, and the overcurrent detection signal are configured to be transmitted from the ECU.

  The first OR circuit OR1 is configured to receive the OFF command signal, the short circuit detection signal, and the overcurrent detection signal, and output the same to the control unit 22 and the timer 28. The first OR circuit OR1 switches the output from low to high when at least one of an OFF command signal, a short circuit detection signal and an overcurrent detection signal is input, and turns off the MOSFET 16 to the control unit 22 and the timer 28. To send a signal instructing.

  In the comparison circuit COM1, the gate voltage Vg of the MOSFET 16 is input to the inverting input terminal (−), the threshold voltage Vth of the reference power supply V10 is input to the non-inverting input terminal (+), and the output thereof is the second OR circuit. It is configured to input to OR2. The comparator circuit COM1 monitors the gate voltage of the MOSFET 16, and when the gate voltage Vg becomes lower than the threshold voltage Vth of the reference power source V10, switches the output from low to high and causes the second OR circuit OR2 to operate. The comparison signal S10 is transmitted.

  The timer 28 is configured such that the output of the first OR circuit OR1 is input and the output thereof is input to the second OR circuit OR2. The timer 28 switches the output from low to high and transmits the timer signal S20 to the second OR circuit OR2 when the elapsed time after receiving the signal from the first OR circuit OR1 reaches the set time. To do. The comparison circuit COM1 outputs the comparison signal S10 from when the signal from the first OR circuit OR1 is transmitted (that is, when the signal instructing turn-off of the MOSFET 16 is transmitted) for the set time set in the timer 28. It is the allowable value before sending. That is, the timer 28 transmits the timer signal S20 to the second OR circuit OR2 instead of the comparison circuit COM1 when the comparison circuit COM1 cannot transmit the comparison signal S10 within the set time for some reason. .

  The second OR circuit OR2 is configured such that the comparison signal S10 from the comparison circuit COM1 and the timer signal S20 from the timer 28 are input, and the output thereof is input to the control unit 22. The second OR circuit OR2 switches its output from low to high when at least one of the comparison signal S10 from the comparison circuit COM1 and the timer signal S20 from the timer 28 is input, and outputs a signal to the control unit 22. Send.

The control unit 22 can execute at least the following three modes.
(1) The control unit 22 turns on and off the on switching element SW1 and the off switching element SW2 so that when the on command signal is received, the on switching element SW1 is turned on and the off switching element SW2 is turned off. Is configured to control.
(2) When the control unit 22 receives the signal from the first OR circuit OR1, it turns on both the ON switching element SW1 and the OFF switching element SW2 at the same time so as to turn ON both the ON switching element SW1 and the OFF switching element SW2. Is configured to control ON / OFF of the switching element SW2.
(3) When receiving the signal from the second OR circuit OR2, the control unit 22 turns off the ON switching element SW1 and turns on the OFF switching element SW2 so that the ON switching element SW1 and the ON switching element SW1 are turned off. Is configured to control ON / OFF of the switching element SW2.

  As described above, when the control unit 22 receives the signal for instructing the turn-off of the MOSFET 16 from the first OR circuit OR1, first, both the ON switching element SW1 and the OFF switching element SW2 are operated in the mode (2). Are turned on at the same time, and thereafter, in accordance with the comparison signal S10 from the comparison circuit COM1 or the timer signal S20 from the timer 28, the on switching element SW1 is turned off and the off switching element SW2 is turned on in the mode (3). It is characterized by doing. The control unit 22 is characterized by executing the two-step control of the above (2) and (3) when turning off the MOSFET 16. Hereinafter, the timing chart when the control unit 22 executes the two-step control based on the comparison signal S10 from the comparison circuit COM1 and the timing when the two-step control is executed based on the timer signal S20 from the timer 28 Each of the charts will be described.

  FIG. 3 is a timing chart when the control unit 22 executes the two-step control based on the comparison signal S10 from the comparison circuit COM1. Here, the ON command is a command executed by the control unit 22 when the ON command signal is high and all of the OFF command signal, the short circuit detection signal and the overcurrent detection signal are low. The OFF command is a command executed by the control unit 22 when the ON command signal is low and any one of the OFF command signal, the short circuit detection signal and the overcurrent detection signal is high.

  First, when an ON command is given, the control unit 22 controls so that the ON switching element SW1 is turned ON and the OFF switching element SW2 is turned OFF (mode (1) above). As a result, the gate voltage Vg of the MOSFET 16 rises to the gate-on voltage, the drain current Id also flows through the MOSFET 16, and the MOSFET 16 is on.

  At timing t1, the control unit 22 receives an OFF command signal from, for example, the ECU. The control unit 22 switches from the ON command to the OFF command, turns on the switching element SW2 for OFF at timing t2, and controls the switching element SW1 for ON and the switching element SW2 for OFF to be simultaneously turned ON (see (2) above). mode). When the ON switching element SW1 and the OFF switching element SW2 are simultaneously turned ON, a series circuit of the ON path resistance element R1 and the OFF path resistance element R2 is formed between the first terminal T1 and the second terminal T2. Therefore, the voltage at the connection point P1 is adjusted to a voltage obtained by dividing the difference voltage between the gate-on voltage V1 at the first terminal T1 and the gate-off voltage V2 at the second terminal T2 by the on-path resistance element R1 and the off-path resistance element R2. It As a result, the gate voltage Vg of the MOSFET 16 decreases, the drain current Id of the MOSFET 16 decreases, and the drain-source voltage Vds of the MOSFET 16 increases. Here, since the gate voltage Vg of the MOSFET 16 is adjusted to a divided voltage higher than the gate-off voltage V2, the change rate of the drain current Id of the MOSFET 16 is relatively small. As a result, immediately after turn-off, the surge voltage applied to the drain-source voltage Vds of the MOSFET 16 is suppressed, and the drain-source voltage Vds of the MOSFET 16 is suppressed from exceeding the element breakdown voltage.

  When the gate voltage Vg of the MOSFET 16 drops and falls below the threshold voltage Vth of the reference power supply V10, the comparison signal S10 output from the comparison circuit COM1 switches from low to high at timing t3. When the comparison signal S10 switches from low to high, the control unit 22 controls the on switching element SW1 to be off (mode (3) above). As a result, the gate voltage Vg of the MOSFET 16 drops to the gate-off voltage V2, the drain current Id of the MOSFET 16 drops, and the drain-source voltage Vds of the MOSFET 16 increases. Here, since the gate voltage Vg of the MOSFET 16 is adjusted to the gate-off voltage V2, the change rate of the drain current Id of the MOSFET 16 is relatively large. As a result, the rate of change of the drain current Id of the MOSFET 16 can be increased during the turn-off process, and the turn-off loss can be reduced. At this stage, since the drain-source voltage Vds of the MOSFET 16 is sufficiently reduced, the drain-source voltage Vds of the MOSFET 16 exceeds the element breakdown voltage even if the change rate of the drain current Id of the MOSFET 16 is large. Can be suppressed.

  As described above, the gate voltage control circuit 20 of the present embodiment can control the gate voltage Vg of the MOSFET 16 in two steps when turning off the MOSFET 16. As a result, the trade-off relationship existing between the switching loss of the MOSFET 16 and the surge voltage can be improved.

  Further, the gate voltage control circuit 20 of the present embodiment turns on the switching element SW1 for turning on and the switching element SW2 for turning off at the same time immediately after turn-off, so that the voltage dividing circuit for the on-path resistance element R1 and the off-path resistance element R2. Can be used to control the voltage applied to the gate of the MOSFET 16. These circuit elements also include conventional gate voltage control circuits. Therefore, the gate voltage control circuit 20 of the present embodiment can control the voltage applied to the gate of the MOSFET 16 immediately after turn-off without increasing the number of circuit elements.

  FIG. 4 is a timing chart when the control unit 22 executes the two-step control based on the timer signal S20 from the timer 28. If the comparison signal S10 is not transmitted from the comparison circuit COM1 for some reason, the voltage of the gate of the MOSFET 16 cannot be lowered to the gate-off voltage V2, and the MOSFET 16 cannot be turned off. A timer 28 is provided to deal with such a situation.

  As shown in FIG. 4, before the gate voltage Vg of the MOSFET 16 falls below the threshold voltage Vth of the reference power supply V10, the elapsed time from the input of the OFF command signal reaches the set time set in the timer 28. Then, the timer signal S20, which is the output of the timer 28, switches from low to high. When the timer signal S20 switches from low to high, the control unit 22 controls the on switching element SW1 to be off (mode (3) above). As a result, the gate voltage Vg of the MOSFET 16 drops to the gate-off voltage V2, the drain current Id of the MOSFET 16 drops, and the drain-source voltage Vds of the MOSFET 16 increases. Thus, even if the comparison signal S10 from the comparison circuit COM1 is not transmitted within the set time of the timer 28 for some reason, the gate voltage Vg of the MOSFET 16 can be lowered to the gate-off voltage V2 during the turn-off. .

  As shown in FIG. 5, the threshold voltage Vth of the reference power supply V10 may be adjustable based on at least one of the output current monitoring signal, the system voltage monitoring signal, and the element temperature signal. Also, the set time set by the timer 28 may be adjustable by the output current monitoring signal, the system voltage monitoring signal, and the element temperature signal. The output current monitoring signal is a signal based on the output current flowing through the output wirings 11a to 11c to which the corresponding MOSFET 16 of the output wirings 11a to 11c (see FIG. 1) is connected. The system voltage monitoring signal is a voltage (see FIG. 1) between the high voltage wiring 12 and the low voltage wiring 14, and is also called a system voltage. The element temperature signal is a signal based on the element temperature of the corresponding MOSFET 16.

  Here, the magnitude of the surge voltage when turning off the MOSFET 16 is the magnitude in which the voltage depending on the product of the change rate of the drain current Id and the inductance of the wiring is superimposed on the system voltage. The change rate of the drain current Id depends on the element temperature and the output current. The reason why the rate of change of the drain current Id depends on the element temperature is that the gate threshold of the MOSFET 16 has a positive or negative temperature characteristic.

Therefore, the threshold voltage Vth of the reference power supply V10 may be adjusted as follows, for example. The specific adjustment amount can be adjusted appropriately.
(1) The threshold voltage Vth of the reference power supply V10 may be adjusted low when the system voltage is high, and adjusted high when the system voltage is low.
(2) When the gate threshold of the MOSFET 16 has a positive temperature characteristic, the threshold voltage Vth of the reference power supply V10 may be adjusted high when the element temperature is high and adjusted low when the element temperature is low.
(3) When the gate threshold of the MOSFET 16 has a negative temperature characteristic, the threshold voltage Vth of the reference power supply V10 may be adjusted low when the element temperature is high, and adjusted high when the element temperature is low.
(4) The threshold voltage Vth of the reference power source V10 may be adjusted low when the output current is large and adjusted high when the output current is small.

Further, the set time set by the timer 28 may be adjusted as follows, for example. The specific adjustment amount can be adjusted appropriately.
(1) The set time set by the timer 28 may be adjusted long when the system voltage is high, and adjusted short when the system voltage is low.
(2) When the gate threshold of the MOSFET 16 has a positive temperature characteristic, the set time set by the timer 28 may be adjusted short when the element temperature is high and adjusted long when the element temperature is low.
(3) When the gate threshold of the MOSFET 16 has a negative temperature characteristic, the set time set by the timer 28 may be adjusted long when the element temperature is high and short when the element temperature is low.
(4) The set time set by the timer 28 may be adjusted long when the output current is large and short when the output current is small.

  Although the embodiments have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above. The technical elements described in the present specification or the drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technique illustrated in the present specification or the drawings achieves a plurality of purposes at the same time, and achieving the one purpose among them has technical utility.

20: Gate voltage control circuit 22: Control circuit 24: On-path circuit 26: Off-path circuit 28: Timer COM1: Comparison circuit OR1: First OR circuit OR2: Second OR circuit R1: On-path resistance element R2: Off Path resistance element SW1: switching element SW2 for ON: switching element T1 for OFF: first terminal T2: second terminal V10: reference power source

Claims (1)

A gate voltage control circuit for controlling the gate voltage of the main switching element,
A first terminal to which a gate-on voltage is applied,
A second terminal to which a gate-off voltage is applied,
An on-path circuit,
An off-path circuit,
And a control unit,
The on-path circuit and the off-path circuit are connected in series between the first terminal and the second terminal,
The connection point of the on-path circuit and the off-path circuit is connected to the gate of the main switching element,
The on-path circuit has an on-switching element and an on-path resistance element connected in series,
The off-path circuit has an off switching element and an off-path resistance element connected in series,
When the control section turns off the main switching element, the on switching element and the on switching element are turned off so that the on switching element and the off switching element are turned on at the same time. A gate voltage control circuit configured to control ON / OFF of a switching element for OFF.

Images