JP2012227825A - Load drive device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce variations in switching loss, voltage surge and peak current by reducing variations in gate voltage gradient.SOLUTION: A control delay operation circuit 6 delays by a delay time the transmission of the switching of an off permission signal from a disabling state to an enabling state to an off holding device 5. After the lapse of the delay time, a stable value of output current of a constant current drive circuit 30 having reached a target value of constant current can be supplied to a gate 1a of a switching element 1. This can reduce variations in gate voltage rise gradient to reduce variations in switching loss, voltage surge and peak current.

Description

  The present invention relates to a load driving device that performs on / off of power supply to a load by controlling on / off of a switching element.

  Conventionally, as a circuit configuration for driving a switching element such as an IGBT by a constant current driving method, for example, there are those shown in Patent Documents 1 and 2.

  The constant current drive circuit disclosed in Patent Document 1 includes an on-side circuit for turning on the IGBT and an off-side circuit for turning off the IGBT, and each has a configuration in which a constant current forming resistor and a MOSFET are connected in series. Yes. When the IGBT is turned on, the MOSFET in the on-side circuit is turned on, the MOSFET in the off-side circuit is turned off to supply a constant current to the gate of the IGBT, and when the IGBT is turned off, the MOSFET in the on-side circuit is turned off and off. The MOSFET in the side circuit is turned on to extract charges from the gate of the IGBT. Each MOSFET is turned on and off by the output of the operational amplifier, and the output of the operational amplifier is adjusted according to the overcurrent detection result in the overcurrent detection circuit unit, thereby preventing the IGBT from being destroyed by the overcurrent. It can be done.

  Further, in the constant current drive circuit disclosed in Patent Document 2, an on-side constant current circuit that turns on an IGBT using a PNP transistor is configured, and an off-side constant current that turns off an IGBT using an NPN transistor. The circuit is configured. In the off-side constant current circuit, a configuration in which NPN transistors are connected in a Darlington connection has been proposed in order to increase driving speed.

Japanese Patent No. 3680722 JP 2009-11049 A

  In the constant current drive circuit disclosed in Patent Document 1, the current supplied to the gate of the IGBT is fed back, so that the accuracy of the constant current can be ensured, and the on-side circuit and the off-side circuit are replaced with MOSFETs. Therefore, higher speed can be expected compared to bipolar transistors. However, Patent Document 1 does not consider anything about the configuration for realizing high-speed driving, the problem, and the solution.

  In the constant current driving circuit disclosed in Patent Document 2, since the on-side constant current circuit and the off-side constant current circuit are configured by bipolar transistors, the response speed is slow and high speed cannot be expected.

  For this reason, the present inventors have intensively studied a load driving device having a constant current driving circuit configuration that can be expected to increase the speed. For example, a circuit configuration shown in FIG. 15 is conceivable as a constant current drive type circuit that can be expected to increase in speed.

  The circuit includes a switching element J1 connected to a load (not shown) and driven to turn on and off based on current supply to the gate J1a, an on-side circuit J3 that turns on the switching element J1 based on power supply from the power source J2, and There is provided an off-side circuit J4 that extracts the charge accumulated in the gate of the switching element J1 when the switch is off. The on-side circuit J3 includes a constant current drive circuit J3a that operates based on power supply from the power supply J2, and the constant current drive circuit J3a is driven based on a constant current drive circuit control signal from a microcomputer (not shown). Then, the switching element J1 is turned on by supplying a constant current to the gate J1a of the switching element J1. The off-side circuit J4 is configured by, for example, a MOSFET, and on / off is controlled based on the off-circuit control signal. When the off-side circuit J4 is turned on, the charge accumulated in the gate J1a of the switching element J1 is a reference point. The switching element J1 is turned off by being pulled out to the second side.

  Further, this circuit includes an off-holding device J5 that prevents erroneous turn-on in which the switching element J1 is erroneously turned on. The off-holding device J5 is a reference that has a predetermined potential with the gate J1a of the switching element J1 in order to prevent the switching element J1 from being erroneously turned on when noise is applied to the gate J1a of the switching element J1 from the power supply J2 side. It is comprised by MOSFET etc. which connect the point 1. The off-holding device J5 is controlled by an off-permission signal, and when the constant current drive circuit control signal switches the on-side circuit J3 from off to on, the off-permission signal is switched from the prohibited state to the permitted state in advance. Release off hold. That is, when the constant current driving circuit control signal is in the prohibited state, the switching element J1 is held off by the off holding device J5, thereby prohibiting the driving of the switching element J1, and when the constant current driving circuit control signal is in the permitted state. The off-holding of the switching element J1 by the off-holding device J5 is released, and the driving of the switching element J1 is permitted. Accordingly, the switching element J1 can be prevented from being turned on even when noise is applied to the gate J1a during the off-holding by the off-holding device J5. When the off-holding is released, the switching element J1 is driven based on the driving of the on-side circuit J3. J1 can be turned on.

  However, in the circuit configured as described above, it takes time until the output current of the constant current drive circuit J3a is stabilized at the target value. For this reason, even if the gate voltage of the switching element J1 exceeds the threshold voltage Vth and the switching element J1 is turned on, the switching element J1 cannot be driven with a constant current, and the gate voltage inclination variation increases, and the switching loss, voltage surge, peak of the switching element J1 There arises a problem that current variation becomes large. This problem will be described with reference to a timing chart showing the operation of the circuit configuration shown in FIG. 15 in FIG.

  As shown in this figure, before the switching element J1 is turned on, the constant current drive circuit control signal is turned off (low level), and when turned on, the constant current drive circuit control signal is turned on (high level). Can be switched. The off-circuit control signal is turned on (high level) before the switching element J1 is turned on, and is turned off (low level) slightly before the switching element J1 is turned on. The off permission signal is a signal whose signal level is reversed with respect to the off circuit control signal, and is in a prohibited state (low level) before turning on the switching element J1, and in a permitted state (high level) slightly before turning on the switching element J1. ).

  When the switching element J1 is switched on, the output current waveform of the constant current drive circuit J3a changes as shown in the figure, and the constant current increases to a target value with a predetermined slope. The inclination at this time varies depending on the responsiveness of the element such as the product-to-product variation of the constant current driving circuit J3a, the responsiveness of the feedback when the constant current is generated by feedback control, the responsiveness of the elements constituting the feedback control circuit, and the like. . For this reason, the output current of the constant current drive circuit J3a has a large slope and reaches a target value, and then overshoots the target value and then settles to the target value, or the slope is small and the activation of the switching element J1 is delayed. Variations occur in some cases. For this reason, the gate injection current of the switching element J1 also varies in inclination like the output current of the constant current drive circuit J3a, and the time until the gate voltage of the switching element J1 reaches the mirror voltage is increased or decreased. To do.

  The slope of the gate voltage determines the switching loss, voltage surge and peak current. The switching loss becomes smaller as the slope of the gate voltage becomes steeper, but has a contradictory relationship in which the voltage surge and the peak current become larger. If the loss is large, it is necessary to adopt a high heat dissipation structure, which increases the cost. In addition, if the voltage surge or the peak current is large, it is necessary to employ a high-resistance element so as not to exceed the breakdown voltage or allowable current of the switching element, resulting in an increase in cost. The switching element drive circuit needs to be designed so that the cost can be suppressed most under the condition that the relationship between the switching loss and the voltage surge / peak current is established. Generally, the circuit responsiveness has large variations in temperature characteristics and between products, and in the above circuit configuration, the gate voltage gradient varies greatly. Therefore, it is necessary to design the switching element J1 with a sufficient margin. Therefore, it is important to reduce the variation in the slope of the gate voltage.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a load driving device that can reduce variations in the slope of the gate voltage, thereby reducing variations in switching loss, voltage surge, and peak current.

  In order to achieve the above object, according to the first aspect of the invention, when the switching element (1) is turned on, the constant current drive circuit (30) is indicated by indicating that the constant current drive circuit control signal is switched from OFF to ON. A constant current is generated in order to turn on the on-side circuit (3), and the off-circuit control signal indicates that the off-side circuit (4) is turned off, and the switching element (1) is turned to the gate (1a). When the current is supplied and the switching element (1) is turned off, the constant current drive circuit control signal is switched from on to off to stop the generation of the constant current in the constant current drive circuit (30). The circuit (3) is turned off and the off circuit (4) is turned on by indicating that the off circuit control signal is switched from off to on, so that the gate (1a) of the switching element (1) is turned on. In the load driving device that extracts the electric charge of the device, when the switching element (1) is turned on, the fact that the off permission signal is switched from the prohibition of the off to the permission is delayed from being transmitted to the off holding device (5). The first control delay calculation circuit (6) includes a first control delay calculation circuit (6). When the predetermined delay time has elapsed since the constant current drive circuit control signal was switched from OFF to ON, the first control delay calculation circuit (6) It is characterized by notifying the off-holding device (5) of switching from prohibition of off to permission.

  In this way, the first control delay calculation circuit (6) delays the fact that the off permission signal is switched from the prohibited state to the permitted state to the off hold device (5) by the delay time. Therefore, after the delay time has elapsed, the output current of the constant current drive circuit (30) that has already reached the target value of the constant current and has become a stable value is supplied to the gate (1a) of the switching element (1). Can be. Therefore, variation in the slope of the gate voltage can be reduced, and variation in switching loss, voltage surge, and peak current can be reduced.

  In the invention according to claim 2, the off-holding device (5) is a MOSFET (50) for controlling on / off between the gate (1a) of the switching element (1) and a reference point at a predetermined potential. It is characterized by.

  The rise of the gate injection current is determined only by the single response speed of the off-holding device (5). For this reason, it is possible to make the off-holding device (5) very fast by configuring it with the MOSFET (50) capable of high speed operation. Therefore, the variation in the slope of the gate voltage can be reduced, and the variation in switching loss, voltage surge and peak current can be reduced.

  According to a third aspect of the present invention, there is provided a drive circuit temperature monitoring section (7) for monitoring the temperature of the constant current drive circuit (30) and generating an output corresponding to the temperature of the constant current drive circuit (30). The first control delay calculation circuit (6) is characterized in that the delay time is set longer as the temperature of the constant current drive circuit (30) becomes higher, based on the output of the drive circuit temperature monitoring unit (7).

  According to such a configuration, the delay time can be set to an optimum length according to the temperature of the constant current drive circuit (30), and compared with the case where the delay time is unnecessarily increased, the off-holding device (5 ) Can be reduced, and the loss and current consumption of the constant current drive circuit (30) can be reduced.

  The invention according to claim 4 includes a switching element temperature monitoring unit (8) for monitoring the temperature of the switching element (1) and generating an output corresponding to the temperature of the switching element (1), and the first control. The delay calculation circuit (6) is characterized in that the delay time is set to be shorter as the temperature of the switching element (1) is lower based on the output of the switching element temperature monitoring unit (8).

  According to such a configuration, the gate injection current of the switching element (1) can be quickly raised at a high temperature and gradually raised at a low temperature. For this reason, the slope of the gate voltage of the switching element (1) also becomes steep at high temperatures and gentle at low temperatures. Thus, by adjusting the slope of the gate voltage to be gentler as the switching element (1) becomes lower in temperature, it is possible to improve the surge breakdown tolerance.

  In the invention according to claim 5, the on-side circuit (3) includes a constant current driving circuit (30) and a reference resistor (31), and the constant current driving circuit (30) is switched between the power source (2) and the switching circuit. A MOSFET (30a) connected in series with the reference resistor (31) between the gate (1a) of the element (1) and controlling on / off between the power source (2) and the gate (1a), and a reference voltage (Vref ), And an operational amplifier (30c) that generates an output so that the potential between the reference resistor (31) and the MOSFET (30a) is close to the reference voltage (Vref). And a current determined by the resistance value of the reference resistor (31) and the reference voltage (Vref) is supplied as a constant current.

  In such a configuration, when a signal indicating that the switching element (1) is turned on is input as a constant current drive circuit control signal, the operational amplifier (30c) is driven and a gate voltage is applied to the MOSFET (30a), A constant current is injected into the gate (1a) of the switching element (1). The constant current at this time is made constant by adjusting the output of the operational amplifier (30c) so that the potential between the reference resistor (31) and the MOSFET (30a) approaches the reference voltage (Vref). Can be feedback controlled.

  According to the sixth aspect of the present invention, the constant current monitoring unit (9) for monitoring the constant current based on the potential between the reference resistor (31) and the MOSFET (30a) and generating an output corresponding to the constant current is provided. The first control delay calculating circuit (6) is characterized in that, based on the output of the constant current monitoring unit (9), the time when the constant current reaches a predetermined target value is set as the timing of the end of the delay time. Yes.

  In this way, it is possible to prevent the constant current from being abandoned through the off-holding device (5) even though the constant current has reached the target value, and to reduce the waste current. it can.

  In the seventh aspect of the invention, when the switching element (1) is turned off, the constant current drive circuit control signal in the on-side circuit (3) is notified to the constant current drive circuit control signal that is switched from on to off. A second control delay calculation circuit (10) for delaying the delay time, and the second control delay calculation circuit (10) is fixed when a predetermined delay time elapses from when the off-circuit control signal is switched from off to on. It is characterized in that the constant current drive circuit (30) in the on-side circuit (3) is notified that the current drive circuit control signal is switched from on to off.

  As described above, even when the charge is extracted, the constant current drive circuit control signal is switched from ON to OFF until the delay time elapses after the OFF circuit control signal is switched from OFF to ON by the second control delay calculation circuit (10). The on-side circuit (3) is not notified of the fact that the switch has been made. Then, after the delay time has passed, it is transmitted to the on-side circuit (3). As a result, the gate is driven in a state where the off-side constant current drive circuit (43) is stable up to the target value, so that the variation in the falling slope of the gate voltage can be reduced, so that the variation in switching loss, voltage surge and current surge can be reduced. Can be achieved.

  In addition, the code | symbol in the bracket | parenthesis of each said means shows the correspondence with the specific means as described in embodiment mentioned later.

1 is a circuit block diagram showing a circuit configuration of a load driving device according to a first embodiment of the present invention. It is the circuit diagram which showed the detailed structure of each part with which the load drive device shown in FIG. 1 is equipped. It is the timing chart which showed the action | operation of the load drive device shown in FIG. It is the circuit diagram which showed the circuit structure of the load drive device which showed the modification of 1st Embodiment of this invention. It is the circuit block diagram which showed the circuit structure of the load drive device concerning 2nd Embodiment of this invention. FIG. 6 is a circuit diagram showing a configuration example of a constant current drive circuit 30 provided in the load drive device shown in FIG. 5. FIG. 6 is a diagram showing changes in the output current waveform, the current flowing through the off-holding device 5 and the gate injection current of the switching element 1 when the constant current drive circuit 30 changes in temperature. It is the circuit block diagram which showed the circuit structure of the load drive device concerning 3rd Embodiment of this invention. It is the circuit diagram which showed the structural example of the switching element 1 with which the load drive device shown in FIG. 8 is equipped. FIG. 4 is a diagram showing changes in an output current waveform, a current flowing through an off-holding device 5, a gate injection current of the switching element 1, and a gate voltage of the switching element 1 when the temperature of the switching element 1 changes. It is the circuit block diagram which showed the circuit structure of the load drive device concerning 4th Embodiment of this invention. It is the circuit block diagram which showed the circuit structure of the load drive device concerning 5th Embodiment of this invention. 13 is a timing chart showing the operation of the load driving device shown in FIG. FIG. 6 is a diagram showing another circuit configuration example of the constant current drive circuit 30 configuring the on-side circuit 3. It is the figure which showed the example of a circuit of the constant current drive system which can anticipate speedup. 16 is a timing chart showing the operation of the circuit configuration shown in FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, the same or equivalent parts are denoted by the same reference numerals in the drawings.

(First embodiment)
A first embodiment of the present invention will be described. FIG. 1 is a circuit block diagram showing a circuit configuration of the load driving device according to the present embodiment. FIG. 2 is a circuit diagram showing a detailed configuration of each unit provided in the load driving device shown in FIG. Hereinafter, the load driving device according to the present embodiment will be described with reference to these drawings.

  As shown in FIG. 1, in the load driving device of the present embodiment, the switching element 1 is controlled to be turned on and off by controlling the injection current to the gate 1 a of the switching element 1, and the power supply to the load is controlled. . As shown in FIG. 2, an IGBT 1b is used as the switching element 1, and the IGBT 1b is controlled to be turned on / off by controlling the injection current to the gate 1a of the IGBT 1b, thereby controlling the power supply to the load. For example, the IGBT 1b is used for controlling charging of a battery in a power converter (not shown). The power converter is configured, for example, such that a smoothing capacitor is connected to a power source and a series circuit having a diode and a battery is connected in parallel to the smoothing capacitor. The collector of the IGBT 1b is connected between the smoothing capacitor and the anode of the diode. While the IGBT 1b is turned off, the battery is charged while maintaining a constant charging voltage with the smoothing capacitor. When turned off, the charge stored in the smoothing capacitor is extracted to stop charging the battery. The IGBT 1b according to the present embodiment can be used as a switching element for controlling charging of a battery serving as a load in such a power conversion device.

  In addition, although the case where IGBT1b was applied as a switching element of the charge control to the battery in a power converter device was demonstrated here, of course, you may apply to the other form which performs on-off control of the connection line to load. In this example, the collector of the IGBT 1b is connected to the power supply side, and the emitter is connected to the GND as the reference point 1. However, the emitter is connected to a portion having a predetermined potential as the reference point 1. May be. That is, a load is connected to either the collector side or the emitter side of the IGBT 1b, but the potential of the reference point 1 changes depending on whether the load is connected to the collector side or the emitter side. For example, if an inverter is configured by providing a plurality of IGBTs 1b, a three-phase motor or the like becomes a load, and the load driving device shown in FIG. 1 can be applied as an upper arm or a lower arm for each of the three phases. If the load driving device shown in FIG. 1 is applied as an upper arm, the collector of the IGBT 1b is connected to a power source, and the emitter is connected to a three-phase motor. If the load driving device shown in FIG. 1 is applied as a lower arm, the collector of the IGBT 1b is connected to the three-phase motor, and the emitter is connected to GND. For this reason, the potential of the reference point 1 changes according to the connection destination of the emitter.

  As shown in FIG. 1, the load driving device includes an on-side circuit 3 that turns on the switching element 1 based on the power supply from the power supply 2, and the extraction of the charge accumulated in the gate 1 a of the switching element 1 when it is off. An off-side circuit 4 is provided.

  The on-side circuit 3 includes a constant current driving circuit 30 that operates based on power supply from the power source 2, and the constant current driving circuit 30 is driven based on a constant current driving circuit control signal from a microcomputer (not shown). Then, by supplying a constant current to the gate 1a of the switching element 1, the switching element 1 is turned on. The off-side circuit 4 is controlled to be turned on / off based on an off-circuit control signal. When the off-side circuit 4 is turned on, the charge accumulated in the gate 1a of the switching element 1 is extracted to the reference point 2 side. Element 1 is turned off.

  As shown in FIG. 2, the on-side circuit 3 is configured to include a reference resistor 31 in addition to the constant current drive circuit 30. In FIG. 2, the constant current drive circuit 30 is surrounded by a broken line, but the constant current drive circuit 30 is represented by a structure in which each element constituting the constant current drive circuit 30 is integrated into one chip. .

  The constant current drive circuit 30 includes a MOSFET 30a, a feedback reference (reference voltage circuit) 30b, and an operational amplifier 30c. The MOSFET 30a constitutes an output element of the constant current drive circuit 30, is constituted by a Pch MOSFET, and is on / off controlled based on the output of the operational amplifier 30c. The feedback reference 30b generates a reference voltage Vref to be compared with the potential between the reference resistor 31 and the MOSFET 30a. The operational amplifier 30c is driven based on a constant current drive circuit control signal input from a microcomputer (not shown). When a signal indicating turning on the IGBT 1b is input as the constant current drive circuit control signal, the gate voltage is applied to the MOSFET 30a. By applying this, a constant current is injected into the gate 1a of the IGBT 1b.

  The reference resistor 31 constitutes a gate resistor and determines the current value of a constant current supplied to the gate 1a of the IGBT 1. That is, the constant current Ig injected into the gate 1a of the IGBT 1b is a value obtained by dividing Vref by the resistance value Rs of the reference resistor 31, so that the current value of the constant current is determined based on the resistance value Rs of the reference resistor 31. .

  In such a configuration, when a signal indicating turning on the IGBT 1b is input as a constant current drive circuit control signal, the operational amplifier 30c is driven to apply a gate voltage to the MOSFET 30a, and a constant current is injected into the gate 1a of the IGBT 1b. Is done. The constant current at this time is feedback controlled so as to become a constant current by adjusting the output of the operational amplifier 30c so that the potential between the reference resistor 31 and the MOSFET 30a approaches the reference voltage Vref.

  Further, the off-side circuit 4 is configured to include a gate resistor 41 and a MOSFET 42. As the MOSFET 42, an Nch MOSFET is used. The off-side circuit 4 is on / off controlled based on an off-circuit control signal. Specifically, an off-circuit control signal is input to the gate of the MOSFET 42. When the off-circuit control signal is turned on (high level), the MOSFET 42 is turned on, and the charge accumulated in the gate 1a of the IGBT 1b is extracted and turned off. When the circuit control signal is turned off (low level), the gate 1a of the IGBT 1b is turned off between the reference point 1 having a predetermined voltage.

  In addition, the load driving device is provided with an off-holding device 5 that prevents erroneous turn-on in which the IGBT 1b is erroneously turned on. The off-holding device 5 connects the gate 1a of the IGBT 1b and the reference point 1 having a predetermined potential to prevent the IGBT 1b from being erroneously turned on when noise is applied to the gate 1a of the IGBT 1b from the power source 2 side. Consists of switches. This switch is on / off controlled based on an off permission signal.

  For example, as shown in FIG. 2, the off-holding device 5 includes a MOSFET 50. In the case of this embodiment, the MOSFET 50 is configured by an Nch MOSFET. The MOSFET 50 is turned on when the off permission signal prohibits the IGBT 1b from being turned on (high level), connects the gate 1a of the IGBT 1b and the reference point 1, and is turned off when the permission state (low level) permits. Thus, the current can be supplied to the gate 1a of the IGBT 1b.

  Further, the load driving device of this embodiment is provided with a control delay calculation circuit 6. The control delay calculation circuit 6 sets a delay time when the off holding device 5 performs the off permission. Specifically, the control delay calculation circuit 6 indicates that an off permission signal output from a microcomputer (not shown) is switched from a prohibited state to a permitted state (on to off) to allow current supply to the gate 1a of the IGBT 1b. Even if it is done, it is prevented from being input to the off hold device 5 for a predetermined delay time. When a predetermined delay time elapses, the control delay calculation circuit 6 informs the off hold device 5 that the off permission signal has been switched from the prohibited state to the permitted state, and turns off the off hold device 5 to turn off the gate 1a of the IGBT 1b. And the reference point 1 are turned off so that current can be supplied to the gate 1a of the IGBT 1b.

  The delay time set by the control delay calculation circuit 6 is set to a time longer than the time required for the output current to reach the target value of the constant current after the constant current drive circuit 30 provided in the on-side circuit 3 is driven. Is done. The drive start of the constant current drive circuit 30 can be detected by inputting a constant current drive circuit control signal, and the timing at which the constant current drive circuit control signal is switched from OFF to ON is determined by the constant current drive circuit 30. This is detected as the drive start timing. The length of the delay time varies depending on the responsiveness of the elements such as variations between products of the constant current driving circuit 30, the responsiveness of constant current feedback control, the responsiveness of the operational amplifier 30c constituting the feedback control circuit, and the like. In consideration of the maximum variation, it is preferable that the constant current is set to the longest time required to reach the target value.

  The load driving device according to the present embodiment is configured by the circuit configuration as described above. FIG. 3 is a timing chart showing the operation of the load driving device according to the present embodiment.

  As shown in this figure, before the switching element 1 is turned on, the constant current drive circuit control signal is turned off (low level), and when turned on, the constant current drive circuit control signal is turned on (high level). Can be switched. The off-circuit control signal is turned on (high level) before the switching element 1 is turned on, and is turned off (low level) slightly before the switching element 1 is turned on. The off permission signal is a signal whose signal level is reversed with respect to the off circuit control signal, and is in a prohibited state (low level) before the switching element 1 is turned on, and in a permitted state (high level) slightly before the switching element 1 is turned on. ). Further, the control delay calculation circuit 6 holds the off permission signal. When it is detected that the constant current drive circuit control signal is switched from off to on, the off permission signal changes from the prohibited state to the permitted state after the delay time has elapsed. The off-holding device 5 is notified of the switching.

  When the switching element 1 is switched on, the output current waveform of the constant current drive circuit 30 changes as shown in the figure, and the constant current increases with a predetermined slope to the target value. The inclination at this time varies depending on the responsiveness of the elements such as variations between products of the constant current driving circuit 30, the responsiveness of the feedback when the constant current is generated by feedback control, the responsiveness of elements constituting the feedback control circuit, and the like. . For this reason, the output current of the constant current drive circuit 30 has a large slope and reaches a target value, and then overshoots the target value and then settles to the target value, or the slope is small and the activation of the switching element 1 is delayed. Variations occur in some cases. For this reason, if this current is used as it is as the gate injection current of the switching element 1, the slope varies as in the case of the output current of the constant current drive circuit 30, and the time until the gate voltage of the switching element 1 reaches the mirror voltage. Will be faster or slower.

  However, in the case of the present embodiment, the control delay calculation circuit 6 delays by the delay time that the off permission signal input from the microcomputer or the like is transmitted to the off holding device 5 from the prohibition state to the permission state. During this, the off-holding device 5 is turned on. For this reason, during the delay time, the output current of the constant current drive circuit 30 can be drawn into the off-holding device 5 so that no current is supplied to the gate 1a of the switching element 1.

  After the delay time elapses, the output current of the constant current driving circuit 30 reaches the target value of the constant current and becomes a stable value. At the same time when the off-holding device 5 is turned off, the target constant current is switched. It can be supplied to the gate 1 a of the element 1. The rising slope of the gate injection current at this time is determined only by the single response speed of the off-holding device 5, and the off-holding device 5 is constituted by the MOSFET 50 capable of high-speed operation, so that it can be very fast. . Therefore, the variation in the slope of the gate voltage is reduced, and the variation in switching loss, voltage surge, and peak current can be reduced.

  As described above, in the load driving device of the present embodiment, the control delay calculation circuit 6 delays the OFF holding device 5 that the OFF permission signal is transmitted from the prohibited state to the permitted state by the delay time. I have to. Therefore, after the delay time has elapsed, the output current of the constant current drive circuit 30 that has already reached the target value of the constant current and has become a stable value can be supplied to the gate 1a of the switching element 1. Therefore, the variation in the slope of the gate voltage can be reduced, and the variation in switching loss, voltage surge and peak current can be reduced.

(Modification of the first embodiment)
In the first embodiment, as shown by broken lines in FIG. 2, each element constituting the constant current drive circuit 30, that is, the MOSFET 30a, the reference voltage circuit 30b, and the operational amplifier 30c are all configured as one chip. However, there is a concern that the MOSFET 30a serving as an output element may generate a large amount of heat due to current flow. That is, during the period in which both the constant current drive circuit 30 and the off-holding device 5 are in the on state, power corresponding to the loss of constant current × power supply voltage is generated in the MOSFET 30a. For this reason, depending on the period length and the switching frequency in which both the constant current drive circuit 30 and the off-holding device 5 are in the on state, the allowable loss of the semiconductor device in the case where the constant current drive circuit 30 is configured by a semiconductor device is exceeded. there is a possibility.

  Therefore, when the constant current drive circuit 30 is configured by a semiconductor device, as shown in FIG. 4, if the reference voltage circuit 30b and the operational amplifier 30c are configured separately, and external discrete components are used, a countermeasure against heat generation is provided. It can be carried out. As a result, it is possible to suppress element destruction associated with heat generation.

(Second Embodiment)
A second embodiment of the present invention will be described. In the present embodiment, control in consideration of temperature information of the constant current drive circuit 30 is performed with respect to the first embodiment, and the other aspects are the same as those in the first embodiment. Only the parts different from the form will be described.

  FIG. 5 is a circuit block diagram showing a circuit configuration of the load driving device according to the present embodiment. FIG. 6 is a circuit diagram showing a configuration example of the constant current drive circuit 30 provided in the load drive device shown in FIG.

  As shown in FIG. 5, in this embodiment, temperature information from the drive circuit temperature monitoring unit 7 is transmitted to the control delay calculation circuit 6, and a delay time corresponding to the temperature information is set by the control delay calculation circuit 6. I am doing so. For example, as shown in FIG. 6, a chip constituting the constant current drive circuit 30 is provided with a temperature sensor 30d, and the output of the temperature sensor 30d is input to the drive circuit temperature monitoring unit 7, and the drive circuit temperature monitoring unit 7 The delay time corresponding to the temperature of the constant current drive circuit 30 is calculated by the control delay calculation circuit 6 by generating an output corresponding to the temperature of the constant current drive circuit 30 from the control delay calculation circuit 6. For example, the temperature characteristic of the forward voltage Vf when a plurality of diodes are connected in series can be used as the temperature sensor 30d. An output corresponding to the temperature can be generated. Then, when notifying the off-holding device 5 that the off-permission signal has been switched from the prohibited state to the permitted state, the device is delayed by a set delay time in consideration of the temperature of the constant current drive circuit 30.

  In general, semiconductor devices tend to have a slow response at high temperatures and a fast response at low temperatures. FIG. 7 shows changes in the output current waveform, the current flowing through the off-holding device 5 and the gate injection current of the switching element 1 when the temperature of the constant current drive circuit 30 changes. As shown in this figure, the output current waveform of the constant current drive circuit 30 varies depending on the temperature of the constant current drive circuit 30, and is compared with the case where the constant current drive circuit 30 is at a normal temperature (for example, about 27 ° C.). If the temperature is low, the increase gradient becomes large and the target value is reached quickly. If the temperature is high, the increase gradient becomes small and the target value is delayed. Correspondingly, the current flowing through the off-holding device 5 also changes. Therefore, as shown in the figure, the delay time is changed according to the temperature of the constant current drive circuit 30, and the delay time is set longer as the temperature increases.

  In this way, the delay time can be set to an optimum length according to the temperature of the constant current drive circuit 30, and compared with the case where the delay time is unnecessarily increased, the discarded current flowing through the off-holding device 5 Can be reduced, and loss and current consumption of the constant current drive circuit 30 can be reduced.

(Third embodiment)
A third embodiment of the present invention will be described. In the present embodiment, control is performed in consideration of the temperature information of the switching element 1 with respect to the first embodiment. The other aspects are the same as those in the first embodiment. Only the different parts will be described.

  FIG. 8 is a circuit block diagram showing a circuit configuration of the load driving device according to the present embodiment. FIG. 9 is a circuit diagram showing a configuration example of the switching element 1 provided in the load driving device shown in FIG.

  As shown in FIG. 8, in this embodiment, temperature information from the switching element temperature monitoring unit 8 is transmitted to the control delay calculation circuit 6, and a delay time corresponding to the temperature information is set by the control delay calculation circuit 6. I am doing so. For example, as shown in FIG. 9, a temperature sensor 1c is provided in a chip constituting the switching element 1, and an output of the temperature sensor 1c is input to the switching element temperature monitoring unit 8, and switching is performed from the switching element temperature monitoring unit 8. By generating an output corresponding to the temperature of the element 1, a delay time corresponding to the temperature of the switching element 1 is calculated by the control delay calculation circuit 6. As the temperature sensor 1c, for example, the temperature characteristic of the forward voltage Vf when a plurality of diodes are connected in series can be used, and the change in the voltage across the plurality of diodes is used as a sensor output to obtain the temperature of the switching element 1. Corresponding output can be generated. Then, when notifying the off-holding device 5 that the off-permission signal has been switched from the prohibited state to the permitted state, it is delayed by a set delay time in consideration of the temperature of the switching element 1.

  Generally, in the switching element 1 such as the IGBT 1b, there is a tendency for a surge to be generated more as the temperature is lower, and it is necessary to design with a sufficient margin against surge breakdown. FIG. 10 shows changes in the output current waveform, the current flowing through the off-holding device 5, the gate injection current of the switching element 1, and the gate voltage of the switching element 1 when the temperature of the switching element 1 changes. As shown in this figure, the delay time set by the control delay calculation circuit 6 is set slower than the time when the output current of the constant current drive circuit 30 reaches the target value at a high temperature, but the delay time becomes shorter as the temperature becomes lower. Even if the output current of the constant current drive circuit 30 does not reach the target value, the off holding device 5 is turned off. In the example of FIG. 10, the delay time is hardly provided at a low temperature, and no current flows through the off-holding device 5.

  In this way, as shown in FIG. 10, the gate injection current of the switching element 1 can be raised quickly when the temperature is high and gradually raised when the temperature is low. For this reason, the rise of the gate voltage of the switching element 1 also becomes steep at a high temperature and gentle at a low temperature. As described above, by adjusting the slope of the gate voltage to be gentler as the switching element 1 becomes lower in temperature, it is possible to improve the surge breakdown tolerance. In this case, the switching loss tends to deteriorate due to the slow rise of the gate voltage, but this is not a problem because the temperature of the switching element 1 is low.

  Note that in the case of a circuit having a characteristic in which the output current of the constant current drive circuit 30 overshoots from the target value, if the delay time is shortened, the slope of the gate voltage of the switching element 1 may be increased. obtain. For this reason, it is preferable to set the delay time according to the characteristics of the circuit.

(Fourth embodiment)
A fourth embodiment of the present invention will be described. In this embodiment, constant current information is fed back with respect to the first embodiment. The other aspects are the same as those in the first embodiment, and therefore only the parts different from the first embodiment will be described.

  FIG. 11 is a diagram illustrating a circuit configuration of the load driving device according to the present embodiment. As shown in this figure, in this embodiment, the potential between the MOSFET 30a and the reference resistor 31 in the constant current drive circuit 30, that is, a value corresponding to the current value of the constant current generated by the constant current drive circuit 30, is set to a constant current. The delay time corresponding to the constant current information is set by the control delay calculation circuit 6. Then, when telling the off-holding device 5 that the off-permission signal has been switched from the prohibited state to the permitted state, it is delayed by a set delay time in consideration of the magnitude of the constant current.

  If the constant current has reached the target value, the constant current supplied from the constant current drive circuit 30 can be prevented from flowing to the reference point 1 through the off-holding device 5 by turning off the off-holding device 5 earlier. For this reason, the constant current generated by the constant current drive circuit 30 is fed back and monitored by the constant current monitoring unit 9, and the timing when the constant current reaches the target value is set as the delay time end timing. In this way, it is possible to prevent the constant current from flowing to the reference point 1 through the off-holding device 5 and being discarded as a constant current even though the constant current has reached the target value. Can be reduced.

  In this case as well, in the case of a circuit with characteristics such that the output current of the constant current drive circuit 30 overshoots from the target value, if the delay time is shortened, the slope of the gate voltage of the switching element 1 is reversed. It can be faster. For this reason, it is preferable to set the delay time according to the characteristics of the circuit.

(Fifth embodiment)
A fifth embodiment of the present invention will be described. In the present embodiment, the same configuration is provided when the switching element 1 is turned off with respect to the first embodiment, and the other aspects are the same as those in the first embodiment. Only different parts will be described.

  FIG. 12 is a circuit block diagram illustrating a circuit configuration of the load driving device according to the present embodiment.

  As shown in FIG. 12, in the present embodiment, the off-side circuit 4 is configured by the constant current driving circuit 43, and the off-circuit control signal instructs the off-side circuit 4 to turn on and the switching element 1 to turn off. Then, the constant current driving circuit 43 extracts charges from the gate of the switching element 1 with a constant current. Even when this charge is extracted, the constant current varies. This variation in constant current causes problems such as switching loss and voltage surge, similar to when switching element 1 is turned on. Therefore, the variation in falling slope of the gate voltage is further reduced, and switching loss, voltage surge, etc. It is preferable to reduce the variation.

  For this reason, in this embodiment, as shown in FIG. 12, an on-side control delay arithmetic circuit 10 is provided to delay the timing of switching the on-side circuit 3 from on to off. The control delay calculation circuit 10 sets a delay time when the on-side circuit 3 is turned off. Specifically, the control delay calculation circuit 10 switches the current supply from the on-side circuit 3 to the gate 1a of the switching element 1 when the constant current drive circuit control signal output from the microcomputer (not shown) is switched from on to off. Even if this is indicated, it is prevented from being input to the on-side circuit 3 for a predetermined delay time, and a constant current is allowed to flow even during the delay time. When a predetermined delay time elapses, the control delay calculation circuit 10 informs the on-side circuit 3 that the constant-current driving circuit control signal has been switched from on to off, and the on-side circuit 3 is turned off to turn off the constant current. Stop supplying.

  The delay time set by the control delay calculation circuit 10 is set to a time longer than the time required for the constant current of the off-side circuit 4 to stabilize after the off-side circuit 4 is started (turned on). The drive start of the off-side circuit 4 can be detected by inputting an off-circuit control signal, and the timing at which the off-circuit control signal is switched from off to on is detected as the drive start timing of the off-side circuit 4. ing. Regarding the length of the delay time, the responsiveness of the elements such as variations between products of the constant current driving circuit 43 provided in the off-side circuit 4, the responsiveness of constant current feedback control, the responsiveness of elements constituting the feedback control circuit, etc. Therefore, in consideration of these maximum variations, it is preferable to set the longest time required for the constant current of the off-side circuit 4 to stabilize.

  The load driving device according to the present embodiment is configured by the circuit configuration as described above. FIG. 13 is a timing chart showing the operation of the load driving device according to the present embodiment.

  As shown in this figure, when switching the switching element 1 from on to off, the constant current drive circuit control signal is switched from on (high level) to off (low level). Correspondingly, the off circuit control signal is a signal whose signal level is reversed from that of the constant current drive circuit control signal, and is switched from off (high level) to (low level). Further, the control delay calculation circuit 10 holds the constant current drive circuit control signal, and even if the constant current drive circuit control signal is switched from on to off, the delay time after the off circuit control signal is switched from off to on. Until the time elapses, the on-side circuit 3 is not notified that the constant current drive circuit control signal has been switched from on to off, but is transmitted to the on-side circuit 3 after the delay time has elapsed.

  When the off-side circuit 4 is turned on, the output current waveform of the constant current drive circuit 43 in the off-side circuit 4 changes as shown in the figure, and the constant current decreases to a target value with a predetermined slope. The inclination at this time varies depending on the responsiveness of the elements such as the product-to-product variation of the constant current driving circuit 43, the responsiveness of the feedback when the constant current is generated by feedback control, the responsiveness of the elements constituting the feedback control circuit, and the like. . For this reason, the output current of the constant current drive circuit 43 has a large inclination and reaches a target value, and then overshoots the target value and then settles to the target value, or the inclination is small and the switching element 1 is turned off late. Variations occur in some cases. For this reason, also with respect to the extraction of the charge from the gate 1a of the switching element 1, the inclination varies similarly to the output current of the constant current drive circuit 43, and the time until the gate voltage of the switching element 1 reaches the mirror voltage is fast. It will become slow and slow.

  However, in the present embodiment, as described above, the constant current drive circuit control signal is switched from on to off until the delay time elapses after the off-circuit control signal is switched from off to on by the control delay arithmetic circuit 10. The switch is not transmitted to the on-side circuit 3 but is transmitted to the on-side circuit 3 after the delay time has elapsed. For this reason, during the delay time, even if the off-side circuit 4 is turned on, the on-side circuit 3 is also turned on to generate a gate injection current. Therefore, electric charges are about to be extracted from the gate 1a of the switching element 1. However, it is compensated and the charge is stored in the gate 1a.

  After the delay time elapses, the output current of the constant current drive circuit 43 of the off-side circuit 4 reaches a target value of the constant current and becomes a stable value. At the same time when the on-side circuit 3 is turned off, the target value is reached. The charge can be extracted from the gate 1a of the switching element 1 based on the constant current. At this time, since the constant current of the off-side circuit 4 has already reached the target value, the variation in the falling slope of the gate voltage can be reduced. Thereby, it becomes possible to reduce variations such as switching loss and voltage surge.

  As described above, in the present embodiment, the off-side circuit 4 is configured by the constant current driving circuit 43, and even after the charge is extracted, the control delay arithmetic circuit 10 switches the off-circuit control signal from off to on. Until the delay time elapses, the on-side circuit 3 is not notified that the constant current drive circuit control signal has been switched from on to off. Then, after the delay time has elapsed, it is transmitted to the on-side circuit 3. As a result, the gate is driven in a state in which the off-side constant current drive circuit 43 is stabilized to the target value, so that the variation in the falling slope of the gate voltage can be reduced, so that the variation such as switching loss and voltage surge can be reduced. Can be achieved.

  Note that, when the off-side circuit 4 is turned on and the charge is extracted from the gate 1a as in the present embodiment, when the amount is supplemented by the constant current of the on-side circuit 3, the constant current of the on-side circuit 3 is compensated. Igon and the constant current Igoff of the off-side circuit 4 need to be Igon> Igoff. If this relationship is satisfied, the gate voltage of the switching element 1 can be prevented from decreasing.

(Other embodiments)
As a modification of the first embodiment, the case where the MOSFET 30a is configured with an external discrete component has been described. However, in the second to fifth embodiments, the MOSFET 30a is configured as an external discrete component to take measures against heat generation. It can be carried out.

  Moreover, although the said 5th Embodiment demonstrated what provided the structure which can make the fall of the gate voltage at the time of turning off the switching element 1 quicker with respect to 1st Embodiment, 2nd-4th Embodiment. A similar configuration can be applied to.

  Moreover, it can combine suitably between said each embodiment. That is, you may combine the structure provided with the drive circuit temperature monitoring part 7 demonstrated in 2nd Embodiment, and the structure provided with the switching element temperature monitoring part 8 demonstrated in 3rd Embodiment. Moreover, it is also possible to combine with the structure provided with the constant current monitoring part 9 demonstrated in 4th Embodiment with respect to the structure of 2nd Embodiment, 3rd Embodiment, or the structure which combined these. Of course, a configuration in which these embodiments are combined may be provided with a configuration that can quickly cause the gate voltage to fall when the switching element 1 described in the fifth embodiment is turned off.

  Furthermore, in each of the above-described embodiments, the circuit configuration of the on-side constant current drive circuit 30 has been described by taking as an example the configuration including the MOSFET 30a, the reference voltage circuit 30b, and the operational amplifier 30c. The current drive circuit 30 may be configured.

  FIG. 14 is a diagram showing another circuit configuration example of the constant current drive circuit 30 that constitutes the ON-side circuit 3. As shown in this figure, voltage dividing resistors 30e and 30f and a switch 30g are connected in series between the power source 2 and the reference point 2, and a reference resistor 31 is connected between the power source 2 and the gate 1a of the switching element 1. And the PNP transistor 30h are connected so that the base of the PNP transistor 30h is connected between the voltage dividing resistors 30e and 30f. In such a configuration, the switch 30g is ON / OFF controlled based on the constant current drive circuit control signal, and when the switch 30g is turned ON, the PNP transistor 30h is operated based on the potential divided by the voltage dividing resistors 30e and 30f. To generate a constant current. Thereby, the gate injection current by a constant current can be supplied to the gate 1a of the switching element 1. The constant current drive circuit 30 can also be configured with such a configuration.

1 switching element 1a gate 1b IGBT
DESCRIPTION OF SYMBOLS 1c Temperature sensor 2 Power supply 3 ON side circuit 4 OFF side circuit 5 OFF holding | maintenance device 6 Control delay calculating circuit 7 Drive circuit temperature monitoring part 8 Switching element temperature monitoring part 9 Constant current monitoring part 10 Control delay calculating circuit 30 Constant current driving circuit 30a MOSFET
30b feedback reference 30c operational amplifier 30d temperature sensor 31 reference resistor 43 constant current drive circuit 50 MOSFET

Claims (7)

A switching element (1) for performing on / off control of a connection line connected to a load based on current supply to the gate (1a);
A constant current driving circuit (30) that is turned on / off based on a constant current driving circuit control signal and generates a constant current based on the constant current driving circuit control signal is generated by the constant current driving circuit (30). An on-side circuit (3) for turning on the switching element (1) by supplying a constant current to the gate (1a) of the switching element (1);
The switching element is turned on / off based on an off-circuit control signal, and the charge accumulated in the gate (1a) of the switching element (1) is extracted based on the supply of a constant current by the constant current drive circuit (30). An off-side circuit (4) for turning off (1);
It is turned off when the off permission signal indicates that it is permitted to be turned off and turned off when it is indicated that the off is prohibited, and even if the on-side circuit (3) is turned on, the off permission signal is turned off. An off-holding device (5) that holds off the switching element (1) by being turned on when indicating that the
When the switching element (1) is turned on, the constant current drive circuit (30) generates a constant current by indicating that the constant current drive circuit control signal is switched from OFF to ON, and the ON side circuit (3 ) And turning off the off-side circuit (4) when the off-circuit control signal indicates off, and supplying current to the gate (1a) of the switching element (1),
When turning off the switching element (1), the constant current driving circuit control signal is switched from on to off to stop the generation of constant current in the constant current driving circuit (30), and the on-side circuit (3) is turned off, and the off-side circuit (4) is turned on by indicating that the off-circuit control signal is switched from off to on, and the charge from the gate (1a) of the switching element (1) is turned on. A load driving device for performing drawing,
A first control delay calculation circuit (6) for delaying the fact that when the switching element (1) is turned on, the fact that the off permission signal is switched from prohibition of off to permission is transmitted to the off holding device (5); And the first control delay calculation circuit (6) switches the off permission signal from prohibition of off to permission when a predetermined delay time elapses from when the constant current drive circuit control signal switches from off to on. Is transmitted to the off-holding device (5).   The off-holding device (5) is a MOSFET (50) for controlling on / off between a gate (1a) of the switching element (1) and a reference point having a predetermined potential. The load drive device described in 1. A drive circuit temperature monitoring unit (7) for monitoring the temperature of the constant current drive circuit (30) and generating an output corresponding to the temperature of the constant current drive circuit (30);
The first control delay calculation circuit (6) sets the delay time longer as the temperature of the constant current drive circuit (30) becomes higher, based on the output of the drive circuit temperature monitoring unit (7). The load driving device according to claim 1 or 2. A switching element temperature monitoring unit (8) for monitoring the temperature of the switching element (1) and generating an output corresponding to the temperature of the switching element (1);
The first control delay calculation circuit (6) sets the delay time to a shorter time as the temperature of the switching element (1) decreases based on the output of the switching element temperature monitoring unit (8). The load driving device according to any one of claims 1 to 3. The on-side circuit (3) includes the constant current drive circuit (30) and a reference resistor (31),
The constant current driving circuit (30) is connected in series with the reference resistor (31) between the power source (2) and the gate (1a) of the switching element (1), and the power source (2) and the gate MOSFET (30a) for controlling on / off with respect to (1a), reference voltage circuit (30b) for generating a reference voltage (Vref), potential between the reference resistor (31) and the MOSFET (30a) An operational amplifier (30c) that generates an output so as to be close to the reference voltage (Vref), and the resistance value of the reference resistor (31) and the reference voltage (Vref) as the constant current 5. The load driving device according to claim 1, wherein the load driving device is configured to flow a current determined by A constant current monitoring unit (9) for monitoring the constant current based on a potential between the reference resistor (31) and the MOSFET (30a) and generating an output corresponding to the constant current;
The first control delay calculation circuit (6) sets the timing of the end of the delay time when the constant current reaches a predetermined target value based on the output of the constant current monitoring unit (9). The load driving device according to claim 5.   When the switching element (1) is turned off, the constant current drive circuit control signal is delayed from being transmitted to the constant current drive circuit (30) in the on-side circuit (3). A second control delay operation circuit (10), and the second control delay operation circuit (10), when a predetermined delay time elapses from when the off-circuit control signal is switched from off to on, The load driving device according to any one of claims 1 to 6, wherein the control signal is transmitted to the constant current drive circuit (30) in the on-side circuit (3) to be switched from on to off.

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