JP5915551B2 - Drive circuit for switching element to be driven - Google Patents

Description

  The present invention relates to a drive circuit for a drive target switching element having an overcurrent protection function.

  As this type of drive circuit, for example, as seen in Patent Document 1 below, when the current (collector current) flowing between the input and output terminals of the semiconductor switching element (IGBT) exceeds a threshold current, the gate voltage is reduced. A device having an overcurrent protection function for protecting a switching element from an overcurrent by forcibly limiting a collector current is known.

JP-A-6-209519

  Here, the present inventors considered setting the threshold current based on the applied voltage (collector-emitter voltage) between the input and output terminals of the switching element. In setting the threshold current, the collector-emitter voltage is used as a parameter because the higher the collector-emitter voltage when limiting the collector current, the greater the surge voltage generated when limiting the collector current. Here, from the viewpoint of maintaining the reliability of the switching element, for example, the maximum value of the collector-emitter voltage assumed when the switching element is used is used as the collector-emitter voltage when setting the threshold current. Conceivable.

  However, when such a setting method is adopted, if the actual collector-emitter voltage is lower than the value assumed when setting the threshold current, the upper limit of the collector current at which the actual collector current can maintain the reliability of the switching element. In spite of being less than the value, the overcurrent protection function is activated. That is, there is a concern that the upper limit value of the collector current that can flow through the switching element is restricted, and the conditions under which the switching element can be used are restricted.

  The present invention has been made in order to solve the above-described problems, and the object thereof is a driving target that can preferably avoid the restriction of the upper limit value of the current that can flow between the input / output terminals of the driving target switching element. It is to provide a driving circuit for a switching element.

  In order to solve the above-mentioned problem, the invention according to claim 1 is detected by the current detection means (56) for detecting the current flowing between the input / output terminals of the drive target switching element (S * #) and the current detection means. Current limiting means (50, 58) forcibly limiting the current flowing between the input / output terminals by discharging the charge of the switching control terminal of the switching element to be driven on condition that the current exceeds the threshold current. , 60, 71) and the higher the applied voltage between the input and output terminals, the higher the applied voltage by the current limiting means, the greater the degree of suppression of the surge voltage that occurs when the current limiting means forcibly limits it. And a processing means for performing a process of changing the restriction method.

  In the said invention, the process means is provided, The restriction | limiting method of the electric current which flows between the said input / output terminals according to the applied voltage between the input / output terminals of a switching element is employ | adopted. For this reason, it can avoid suitably that the upper limit of the electric current which can be circulated between the input-output terminals of a drive object switching element is restricted.

The block diagram of the control system concerning 1st Embodiment. The block diagram of the drive unit concerning the embodiment. The time chart which shows an example of transition of the output voltage of a boost converter. The flowchart which shows the procedure of the software interruption | blocking process concerning 1st Embodiment. The time chart which shows an example of the soft interruption | blocking process concerning the embodiment. The block diagram of the drive unit concerning 2nd Embodiment. The flowchart which shows the procedure of the soft interruption | blocking process concerning the embodiment. The block diagram of the drive unit concerning 3rd Embodiment. The flowchart which shows the procedure of the soft interruption | blocking process concerning the embodiment. The block diagram of the drive unit concerning 4th Embodiment. The flowchart which shows the procedure of the soft interruption | blocking process concerning the embodiment. The time chart which shows an example of the soft interruption | blocking process concerning the embodiment. The block diagram of the drive unit concerning 5th Embodiment. The flowchart which shows the procedure of the soft interruption | blocking process concerning the embodiment. The block diagram of the drive unit concerning 6th Embodiment. The flowchart which shows the procedure of the soft interruption | blocking process concerning the embodiment. The figure which shows the selection method of the resistance value of the path | route for soft interruption | blocking concerning other embodiment. The figure which shows the selection method of the threshold voltage concerning other embodiment.

(First embodiment)
DESCRIPTION OF EMBODIMENTS Hereinafter, a first embodiment in which a drive circuit of a drive target switching element according to the present invention is applied to a vehicle including a rotating machine as an in-vehicle main machine will be described with reference to the drawings.

  As shown in FIG. 1, the motor generator 10 is an in-vehicle main machine and is connected to drive wheels (not shown). The motor generator 10 is connected to the high voltage battery 12 via an inverter IV and a boost converter CV as a DC power source. Here, boost converter CV includes a capacitor C, a pair of switching elements Scp and Scn connected in parallel to capacitor C, and a reactor that connects a connection point of the pair of switching elements Scp and Scn and the positive electrode of high-voltage battery 12. L. Specifically, the boost converter CV changes the voltage (for example, 288V) of the high voltage battery 12 to a predetermined voltage (for example, “650V”) by turning on (closing) or turning off (opening) the switching elements Scp, Scn. It has a function of boosting as an upper limit.

  On the other hand, the inverter IV includes a series connection body of a high potential side switching element S * p (* = u, v, w) and a low potential side switching element S * n connected in parallel to the boost converter CV. Specifically, the inverter IV includes a series connection body of the switching elements Sup and Sun, a series connection body of the switching elements Svp and Svn, and a series connection body of the switching elements Swp and Swn. The connection points are connected to the U, V, and W phases of the motor generator 10, respectively. In the present embodiment, the switching element S * # (# = p, n) constituting the inverter IV corresponds to a “driving element switching element”.

  Incidentally, in the present embodiment, a voltage control type is used as the switching element S ¥ # (¥ = u, v, w, c), and more specifically, an IGBT is used. A free wheel diode D ¥ # is connected in reverse parallel to the switching element S ¥ #.

  Control device 14 powers low-voltage battery 16 and operates inverter IV and boost converter CV to control the control amount (torque) of motor generator 10 to its command value (torque command value). Specifically, the control device 14 outputs operation signals gcp and gcn to the drive unit DU so as to turn on and off the switching elements Scp and Scn of the boost converter CV, and the switching elements Sup, Sun, Svp, Operation signals gup, gun, gvp, gvn, gwp, and gwn are output to the drive unit DU to turn on / off Svn, Swp, and Swn. Here, the high-potential side operation signal g ¥ p and the corresponding low-potential side operation signal g ¥ n are complementary to each other. In other words, the high-potential side switching element S ¥ p and the corresponding low-potential side switching element S ¥ n are alternately turned on.

  Note that the output voltage of boost converter CV (input voltage of inverter IV) tends to be higher as the torque command value is higher. Further, the high voltage system including the high voltage battery 12 and the low voltage system including the low voltage battery 16 are insulated from each other, and transmission / reception of signals between them is an interface 18 including an insulating element such as a photocoupler. Is done through.

  Next, the configuration of the drive unit DU included in the inverter IV will be described with reference to FIG.

  As shown in the figure, the drive unit DU includes a drive IC 20 which is a one-chip semiconductor integrated circuit, a constant voltage power supply 22 having a predetermined terminal voltage VH (for example, 15 V), a constant current drive circuit 24, and the like. . The constant current drive circuit 24 includes resistors 26 and 28, an operational amplifier 30, a constant current power source 32, and a P-channel MOSFET (hereinafter, charging switching element 34).

  Specifically, one end of the resistor 26 is connected to the constant voltage power source 22, and the other end is connected to the switching element via the first terminal T 1 of the drive IC 20, the charging switching element 34, and the second terminal T 2 of the drive IC 20. It is connected to the open / close control terminal (gate) of S * #. The connection point between the resistor 26 and the constant voltage power supply 22 is connected to the output terminal (emitter) of the switching element S * # via the third terminal T3 of the drive IC 20, the resistor 28, and the constant current power supply 32. Yes. Further, the connection point of the resistor 28 and the constant current power supply 32 is connected to the non-inverting input terminal of the operational amplifier 30, and the inverting input terminal of the operational amplifier 30 is connected to the connection point of the first terminal T 1 and the charging switching element 34. Has been. According to such a configuration, the potential at the connection point between the first terminal T1 and the charging switching element 34 is held at the potential at the connection point between the resistor 28 and the constant current power supply 32 during the period in which the enable signal is input to the operational amplifier 30. The charging current of the gate can be set to a constant value. That is, the charging process of the gate of the switching element S * # can be performed by constant current control.

  The gate of the switching element S * # is connected to the emitter via the discharging resistor 38, the fifth terminal T5 of the drive IC 20 and an N-channel MOSFET (hereinafter, discharging switching element 40). Here, in the present embodiment, the path from the gate to the emitter through the discharge resistor 38, the fifth terminal T5, and the discharge switching element 40 is normally set to the OFF state of the switching element S * #. A “normal-time discharge path Ldis” used for time switching is configured. Here, the normal time is when a charging process or a discharging process, which will be described later, is performed based on an ON operation command or an OFF operation command.

  The gate of the switching element S * # is also connected to the clamp circuit 42 via the sixth terminal T6 of the drive IC 20. The clamp circuit 42 includes an N-channel MOSFET (hereinafter, clamp switching element 44), an operational amplifier 46 (high-speed operational amplifier), and a power supply 48. Specifically, the sixth terminal T6 is connected to the emitter via the clamping switching element 44. The connection point between the sixth terminal T6 and the clamping switching element 44 is connected to the non-inverting input terminal of the operational amplifier 46. The inverting input terminal of the operational amplifier 46 is connected to the positive side of the power source 48, and the negative side of the power source 48 is connected to the emitter. Note that the terminal voltage of the power supply 48 (hereinafter referred to as a clamp voltage) is switched to a voltage (for example, 12.5 V) at which current does not flow so that the reliability of the switching element S * # is excessively reduced in a short time. It is set to a value that limits the applied voltage (gate voltage) at the switching control terminal of the element S * #. In the present embodiment, the clamp voltage is specifically set to a voltage equal to or higher than the mirror voltage of the switching element S * # and lower than the upper limit voltage of the gate voltage Vge (terminal voltage VH of the constant voltage power supply 22). Has been.

  The gate of the switching element S * # is further connected to the soft cutoff circuit 50 via the seventh terminal T7 of the drive IC 20. The soft cutoff circuit 50 includes a first soft cutoff resistor 52a, a second soft cutoff resistor 52b, a first soft cutoff switching element 54a, and a second soft cutoff switching element 54b. Specifically, one end of the first soft cutoff resistor 52a is connected to the seventh terminal T7, and the other end is connected to the emitter via the first soft cutoff switching element 54a. One end of the second soft cutoff resistor 52b is connected to the seventh terminal T7, and the other end is connected to the emitter via the second soft cutoff switching element 54b. In the present embodiment, N-channel MOSFETs are used as the first and second soft cutoff resistors 52a and 52b.

  Incidentally, in the present embodiment, the path from the gate to the emitter via the seventh terminal T7 and the soft cutoff circuit 50 constitutes the “soft cutoff path Lcut”.

  The switching element S * # is a sense terminal that outputs a minute current (for example, “1/10000” of the collector current Ice) having a correlation with a current flowing between the input terminal (collector) and the emitter (hereinafter referred to as a collector current Ice). St is provided. The sense terminal St is connected to the emitter via a resistor (sense resistor 56). As a result, a voltage drop is generated in the sense resistor 56 due to a small current output from the sense terminal St. Therefore, the potential on the sense terminal St side of the sense resistor 56 (hereinafter referred to as the sense voltage Vse) is correlated with the collector current. State quantity. In this embodiment, the sense resistor 56 constitutes “current detection means”. In the present embodiment, the sense voltage Vse when the potential on the sense terminal St side of both ends of the sense resistor 56 is higher than the potential of the emitter is defined as positive.

  The sense voltage Vse is input to the non-inverting input terminal of the comparator 58 provided in the drive IC 20 via the eighth terminal T8 of the drive IC 20. A terminal voltage of the power supply 60 (hereinafter, threshold voltage Vth) is input to the inverting input terminal of the comparator 58. The output signal Sig of the comparator 58 is input to the drive control unit 36. Here, the threshold voltage Vth is set to, for example, the lower limit value of the sense voltage Vse when the collector current Ice flows in which the reliability of the switching element S * # cannot be maintained. In the present embodiment, the threshold voltage Vth corresponds to “threshold current”.

  A temperature sensitive diode SD * # for detecting the temperature of the switching element S * # (hereinafter, element temperature) is provided in the vicinity of the switching element S * #. The voltage between the terminals of the temperature sensitive diode SD * # is taken into the temperature detection unit 62 provided in the drive IC 20 via the ninth and tenth terminals T9 and T10 of the drive IC 20. The temperature detector 62 outputs the element temperature calculated based on the voltage between the terminals to the drive controller 36. In the present embodiment, the temperature sensitive diode SD * # and the temperature detection unit 62 constitute a “temperature detection means”.

  The collector-emitter voltage is detected by the voltage detection unit 64 provided in the drive IC 20 via the eleventh terminal T11 of the drive IC 20. The voltage detection unit 64 outputs the detected collector-emitter voltage Vce to the drive control unit 36. In the present embodiment, the voltage detector 64 constitutes a “voltage detector”.

  The charging switching element 34 and the discharging switching element 40 are operated by the drive control unit 36. The drive control unit 36 performs switching by alternately turning on and off the charging switching element 34 and the discharging switching element 40 based on the operation signal g * # input via the twelfth terminal T12 of the drive IC 20. Drive element S * #. Specifically, when the operation signal g * # is an ON operation command, the discharge switching element 40 is turned OFF, and the charge switching element 34 is turned ON by outputting an enable signal to the operational amplifier 30. Process. Thereby, switching element S * # is switched to an ON state (closed state). On the other hand, when the operation signal g * # is an off operation command, the discharging switching element 40 is switched to an on operation, and by stopping the output of the enable signal, the charging switching element 34 is switched to an off operation. Discharge treatment is performed. Thereby, switching element S * # is switched to an OFF state (open state).

  The drive control unit 36 further performs an overcurrent protection process based on the gate voltage Vge input through the second terminal T2, the sense voltage Vse input through the eighth terminal T8, and the like. This process is a process including a clamp process and a soft shut-off process.

  First, the clamp process will be described. This process is performed before the gate voltage Vge reaches the terminal voltage VH of the constant voltage power supply 22 under the situation where the operation signal g * # is an ON operation command and the charging process is performed. This is a process of turning on the clamp switching element 44 by outputting an enable signal to the operational amplifier 46 over a clamp filter time (for example, 1.6 μsec). According to this process, for example, when the upper and lower arms are short-circuited, the collector current Ice flowing through the switching element S * # can be limited until the switching element S * # is switched to the OFF state by the soft cutoff process described later. it can.

  Next, the soft shutoff process will be described. In this process, when it is determined that the period in which the logic of the output signal of the comparator 58 is “H” has continued for the specified time Tα, the charging switching element 34 and the discharging switching element 40 are turned off, and the first This is a process of turning on the soft cutoff switching element 54a or the second soft cutoff switching element 54b. By executing the soft shut-off process, the switching element S * # is forcibly turned off and the flow of the collector current is shut off. In the present embodiment, the soft cutoff circuit 50, the comparator 58, and the power source 60 constitute “current limiting means”.

  Here, the first and second soft cutoff resistors 52a and 52b are members for increasing the resistance value of the discharge path of the gate charge. This is because, under a situation where the collector current Ice is excessive, if the speed at which the switching element S * # is switched from the on state to the off state, in other words, the cutoff speed between the collector and the emitter is increased, the surge voltage is increased. This is in view of the possibility of being excessive. In the present embodiment, the resistance value Ra of the first soft-blocking resistor 52a is set higher than the resistance value Rb of the second soft-blocking resistor 52b, and the resistance of the second soft-blocking resistor 52b The value Rb is set higher than the resistance value Rdis of the discharging resistor 38.

  Subsequently, the soft blocking process will be further described.

  In the present embodiment, the higher the collector-emitter voltage Vce detected by the voltage detector 64, the greater the degree of suppression of the surge voltage generated when the collector current is forcibly cut off by the soft cut-off process. Change the blocking method. Specifically, as the collector-emitter voltage Vce is higher, the resistance value of the soft cutoff path Lcut is increased. The inventors of the present invention increase the surge voltage generated when the collector current is cut off as the input voltage of the inverter IV is higher, and the input voltage of the inverter IV changes each time depending on the torque to be output from the motor generator 10. In view of this, a method of increasing the resistance value was adopted. FIG. 3 shows an example in which the input voltage of the inverter IV changes each time.

  FIG. 4 shows the procedure of the soft shutoff process according to this embodiment. This process is repeatedly executed by the drive control unit 36 at a predetermined cycle, for example. Since the drive control unit 36 according to the present embodiment is hardware, the process shown in FIG. 4 is actually executed by a logic circuit.

  In this series of processing, first, in step S10, it is determined whether or not the operation signal g * # is an off operation command. This process is a process for determining whether or not the collector-emitter voltage Vce (input voltage of the inverter IV) can be detected during the period in which the switching element S * # is turned off.

  If an affirmative determination is made in step S10, the process proceeds to step S12, in which it is determined whether or not the collector-emitter voltage Vce is equal to or less than the specified voltage Vα. This process is a process for determining whether or not the surge voltage generated when the collector current is cut off by the soft cut-off process is increased. Here, the collector-emitter voltage Vce during the period in which the off operation command is issued is used because the higher the input voltage of the inverter IV, the surge voltage generated when the switching element S * # is switched to the off state by the soft shutoff process. Is based on growing.

  If an affirmative determination is made in step S12, it is determined that the surge voltage generated when the collector current is cut off does not increase, and the process proceeds to step S14. In step S14, the second soft cutoff switching element 54b is selected as the soft cutoff switching element used in the soft cutoff processing. As a result, the gate charge discharge rate can be increased when the soft shutoff process is performed thereafter.

  On the other hand, if a negative determination is made in step S12, it is determined that the surge voltage may increase, and the process proceeds to step S16. In step S16, the first soft cutoff switching element 54a is selected as the soft cutoff switching element used in the soft cutoff processing. As a result, when the soft shutoff process is performed thereafter, the discharge rate of the gate charge can be lowered.

  When the processes of steps S14 and S16 are completed, or when a negative determination is made in step S10, the process proceeds to step S18, and the logic of the output signal Sig of the comparator 58 continues to be “H” for a specified time Tα. It is determined whether or not. If an affirmative determination is made in step S18, the process proceeds to step S20, and one of the first and second soft cutoff switching elements 54a and 54b selected in the process of step S14 or S16 is switched to the on operation. Further, the charging switching element 34, the discharging switching element 40, and the clamping switching element 44 are switched to the off operation.

  In a succeeding step S22, processing for outputting a fail signal FL is performed. The fail signal FL is output to the low voltage system (control device 14) via the thirteenth terminal T13 of the drive IC 20 shown in FIG. The fail signal FL shuts down the inverter IV and the boost converter CV.

  If a negative determination is made in step S18, or if the process of step S22 is completed, this series of processes is temporarily terminated.

  Next, the effect of the soft blocking process according to the present embodiment will be described with reference to FIG. Here, FIG. 5 shows transitions of the gate voltage Vge, the collector-emitter voltage Vce, the sense voltage Vse, and the collector current Ice.

  In the illustrated example, the sense voltage Vse exceeds the threshold voltage Vth at time t1, and then the collector current Ice is started to be cut off by the soft cut-off process at time t2. Here, with respect to the collector-emitter voltage Vce of FIG. 5, the waveform in the case of performing the soft cutoff processing by selecting the second soft cutoff switching element 54b is shown by a solid line, and the first soft cutoff switching element 54a is shown. The waveform when soft cutoff processing is performed by selecting is shown by a broken line. By increasing the resistance value Rcut of the soft cutoff path Lcut, the surge voltage can be reduced by a predetermined value ΔV. In the figure, the transition of the collector current Ice when the first soft cutoff switching element 54a is selected and the soft cutoff processing is performed is indicated by a one-dot chain line.

  According to the embodiment described in detail above, the following effects can be obtained.

  (1) When it is determined that the collector-emitter voltage Vce during the period in which the off operation command is issued is equal to or lower than the specified voltage Vα, the second soft cutoff switching element 54b is selected and the soft cutoff processing is performed. On the other hand, when it is determined that the collector-emitter voltage Vce exceeds the specified voltage Vα, the first soft cutoff switching element 54a is selected to perform the soft cutoff processing. According to such a process, since the protection method of the switching element S * # can be changed according to the input voltage of the inverter IV, the surge voltage in the case where the switching element S * # is switched to the OFF state by the soft cutoff process. While suppressing the increase, it is possible to preferably avoid the restriction of the upper limit value of the collector current that can flow through the switching element S * #. Therefore, it is possible to avoid that the usable condition of the switching element S * # is restricted.

  (2) A control system in which a boost converter CV is connected to the input side of the inverter IV is adopted. In such a system, the input voltage of the inverter IV can change each time according to the torque command value. For this reason, the utility value of this embodiment which changes the resistance value of the soft interruption | blocking path | route Lcut according to the collector-emitter voltage Vce is high.

(Second Embodiment)
Hereinafter, the second embodiment will be described with reference to the drawings with a focus on differences from the first embodiment.

  In the present embodiment, the selection method of the switching element for soft cutoff used in the soft cutoff process is changed.

  FIG. 6 shows a configuration of the drive unit DU according to the present embodiment. In FIG. 6, the same members as those shown in FIG. 2 are given the same reference numerals for the sake of convenience.

  As illustrated, the drive IC 20 further includes a memory 66. The memory 66 stores the threshold temperature Sth in relation to the collector-emitter voltage Vce so that the assumed element temperature (hereinafter, threshold temperature Sth) increases as the collector-emitter voltage Vce increases. Temperature storage means ". Here, the reason why the threshold temperature Sth is stored in the memory 66 is to use it in the soft shut-off process described later.

  The threshold temperature Sth may be the maximum value of the element temperature when the switching element S * # is driven by the above charging process and discharging process, for example. In the present embodiment, as the memory 66, a means capable of holding information without supplying power is used. Specifically, a nonvolatile memory (for example, EEPROM (registered trademark) or flash memory) is used. Yes.

  FIG. 7 shows the procedure of the soft shutoff process according to this embodiment. This process is repeatedly executed by the drive control unit 36 at a predetermined cycle, for example. In FIG. 7, the same steps as those shown in FIG. 4 are given the same step numbers for the sake of convenience. Further, since the drive control unit 36 according to the present embodiment is hardware, the processing shown in FIG. 7 is actually executed by a logic circuit.

  In this series of processes, if an affirmative determination is made in step S12, the process proceeds to step S24, and the threshold temperature Sth corresponding to the collector-emitter voltage Vce is selected from the threshold temperatures Sth stored in the memory 66. Specifically, a higher threshold temperature Sth is selected as the collector-emitter voltage Vce is higher. This is because the element temperature increases as the input voltage of the inverter IV increases. Note that the threshold temperature Sth may be selected from, for example, a map in which the threshold temperature Sth and the collector-emitter voltage Vce are related. In the present embodiment, the process of this step constitutes “temperature selection means”.

  In a succeeding step S26, it is determined whether or not the element temperature Sd is equal to or lower than the threshold temperature Sth. This process is a process for permitting the selection of the second soft cutoff switching element 54b as the soft cutoff switching element used in the soft cutoff process. This process is a process for avoiding a decrease in the reliability of the switching element S * #.

  That is, for example, when some abnormality occurs in the temperature sensitive diode SD * #, the temperature detection unit 62, or the like, the detected collector-emitter voltage Vce can be lower than the actual collector-emitter voltage. In this case, it is determined that the surge voltage does not increase when the collector current is cut off by the soft cut-off process. As the soft cutoff switching element, the second soft cutoff switching element 54b having the higher gate charge discharge rate is selected from the first and second soft cutoff switching elements 54a and 54b. Here, when the second soft cutoff switching element 54b is turned on by the soft cutoff process, the discharge rate of the gate charge is increased under a situation where the actual collector-emitter voltage is high, and thus a surge voltage is assumed. Can be greater than In this case, the surge voltage exceeds the upper limit value that can maintain the reliability of the switching element S * #, and the reliability of the switching element S * # may be reduced. In order to cope with such a situation, processing of steps S24 and S26 is provided. In the present embodiment, the processing in step S26 constitutes “permission means”.

  If an affirmative determination is made in step S26, use of the second soft cutoff switching element 54b (increase in discharge speed) is permitted, and the process proceeds to step S14. On the other hand, if a negative determination is made in step S26, the use of the second soft cutoff switching element 54b is prohibited. Therefore, in step S16, the first soft cutoff switching element 54a is selected.

  If a negative determination is made in step S18, or if the process of step S22 is completed, this series of processes is temporarily terminated.

  According to the present embodiment described above, the following effects can be obtained in addition to the effects obtained in the first embodiment.

  (3) When it is determined that the collector-emitter voltage Vce is equal to or lower than the specified voltage Vα and the element temperature Sd is equal to or lower than the threshold temperature Sth, as the soft cutoff switching element S * # used in the soft cutoff processing, The second soft cutoff switching element 54b was selected. For this reason, even when the detected collector-emitter voltage Vce is lower than the actual collector-emitter voltage, it is possible to avoid an increase in surge voltage when the soft cutoff process is performed. Thereby, it can avoid that the reliability of switching element S * # falls.

(Third embodiment)
Hereinafter, the third embodiment will be described with reference to the drawings with a focus on differences from the first embodiment.

  In this embodiment, the method for changing the resistance value of the soft cutoff path Lcut is changed.

  FIG. 8 shows a configuration of the drive unit DU according to the present embodiment. In FIG. 8, the same members as those shown in FIG. 2 are given the same reference numerals for the sake of convenience.

  As illustrated, the soft cutoff circuit 50 according to the present embodiment includes a soft cutoff resistor 68 and an N-channel MOSFET (hereinafter, a soft cutoff switching element 70). Specifically, one end of the soft cutoff resistor 68 is connected to the seventh terminal T7, and the other end is connected to the emitter via the soft cutoff switching element 70. Here, the resistance value Rc of the soft blocking resistor 68 is set higher than the resistance value Rdis of the discharging resistor 38. In the present embodiment, the soft cutoff switching element 70 constitutes “resistance value changing means”.

  In the present embodiment, the drive IC 20 includes the memory 66 described in the first embodiment. Here, in the present embodiment, the memory 66 has the above resistance in relation to the collector-emitter voltage Vce so that the resistance value Rcut of the soft cutoff path Lcut increases as the collector-emitter voltage Vce increases. The value Rcut is stored. In the present embodiment, the memory 66 constitutes “resistance value storage means”.

  FIG. 9 shows the procedure of the soft shutoff process according to this embodiment. This process is repeatedly executed by the drive control unit 36 at a predetermined cycle, for example. In FIG. 9, the same steps as those shown in FIG. 4 are given the same step numbers for the sake of convenience. Further, since the drive control unit 36 according to the present embodiment is hardware, the processing shown in FIG. 9 is actually executed by a logic circuit.

  In this series of processes, when an affirmative determination is made in step S10, the process proceeds to step S28, and the resistance value corresponding to the collector-emitter voltage Vce is selected from the resistance value Rcut of the soft cutoff path stored in the memory 66. Select Rcut. Specifically, the higher the resistance value Rcut is selected as the collector-emitter voltage Vce is higher. Note that the resistance value Rcut of the soft cutoff path may be selected from, for example, a map in which the resistance value Rcut is related to the emitter-emitter voltage Vce. In this embodiment, the process of this step constitutes “resistance value selection means”.

  When the process of step S28 is completed or when a negative determination is made in step S10, the process proceeds to step S18. If an affirmative determination is made in step S18, the process proceeds to step S30. In step S30, the gate voltage of the soft cutoff switching element 70 is manipulated so that the actual resistance value of the soft cutoff path Lcut becomes the resistance value Rcut selected in step S28. The on-resistance ΔRon is adjusted. This adjustment method is a method in consideration of the addition value of the resistance value Rc of the soft cutoff resistor 68 and the on-resistance ΔRon becomes the resistance value Rcut of the soft cutoff path. Here, the gate voltage of the soft cutoff switching element 70 is manipulated so that the on-resistance ΔRon increases as the collector-emitter voltage Vce increases. Incidentally, in the process of this step, the gate voltage of the soft cutoff switching element 70 is set to a voltage for driving the soft cutoff switching element 70 in the saturation region. Here, the saturation region is a region where the drain current is constant regardless of the magnitude of the drain-source voltage of the soft cutoff switching element 70.

  When the process of step S30 is completed, the process proceeds to step S22.

  If a negative determination is made in step S18, or if the process of step S22 is completed, this series of processes is temporarily terminated.

  According to the present embodiment described above, the following effects can be obtained in addition to the effects obtained in the first embodiment.

  (4) Using the resistance value Rcut of the soft cutoff path stored in the memory 66, the resistance value Rcut of the soft cutoff path corresponding to the collector-emitter voltage Vce was selected. Then, the gate voltage of the soft cutoff switching element 70 is manipulated so that the actual resistance value of the soft cutoff path Lcut becomes the selected resistance value Rcut. By providing the memory 66, the resistance value Rcut can be set continuously according to the collector-emitter voltage Vce. For this reason, the upper limit value of the collector current that can be circulated to the switching element S * # is restricted while suitably suppressing an increase in surge voltage when the switching element S * # is switched to the OFF state by the soft cutoff process. Can be avoided more suitably.

(Fourth embodiment)
Hereinafter, the fourth embodiment will be described with reference to the drawings with a focus on differences from the first embodiment.

  In the present embodiment, the configuration in which the resistance value of the soft cutoff path Lcut is changed as a configuration in which the forced cutoff method is changed so that the degree of suppression of the surge voltage generated when the collector current is forcibly cut off is increased. Instead, a configuration in which the threshold voltage Vth is changed is adopted.

  FIG. 10 shows the configuration of the drive unit DU according to the present embodiment. In FIG. 10, the same members as those shown in FIG. 2 are given the same reference numerals for the sake of convenience.

  As shown in the figure, the drive IC 20 includes the circuit shown in FIG. 8 of the third embodiment as the soft cutoff circuit 50. However, in this embodiment, as the gate voltage of the soft cutoff switching element 70 when the soft cutoff switching element 70 is turned on, the drain current is increased as the voltage between the drain and the source of the soft cutoff switching element 70 increases. A voltage for driving the soft cutoff switching element 70 is set in the non-saturation region where the increase of the current is increased. In this case, the ON resistance of the soft cutoff switching element 70 when the soft cutoff switching element 70 is turned on is substantially zero.

  Further, the drive IC 20 includes a threshold voltage generation circuit 71 instead of the power supply 60 as a member for generating the threshold voltage Vth. The threshold voltage generation circuit 71 includes a power source 72, first to fourth resistors 74a to 74d, and a pair of N-channel MOSFETs (hereinafter, a first switch 76a and a second switch 76b). Specifically, the positive electrode of the power source 72 is connected to the emitter via a series connection body of a first resistor 74a, a second resistor 74b, and a first switch 76a. The positive electrode of the power source 72 is connected to the emitter via a serial connection body of a third resistor 74c, a fourth resistor 74d, and a second switch 76b.

  A connection point between the first resistor 74 a and the second resistor 74 b and a connection point between the third resistor 74 c and the fourth resistor 74 d are connected to the inverting input terminal of the comparator 58. Further, the first switch 76 a and the second switch 76 b are operated by the drive control unit 36.

  Here, in the present embodiment, the resistance value R1 of the second resistor 74b is set lower than the resistance value R2 of the fourth resistor 74d. Therefore, the threshold voltage (hereinafter referred to as the first threshold voltage V1) when the first switch 76a is turned on and the second switch 76b is turned off is the same as when the first switch 76a is turned off and It becomes higher than the threshold voltage (hereinafter referred to as the second threshold voltage V2) when the second switch 76b is turned on.

  FIG. 11 shows the procedure of the soft shutoff process according to the present embodiment. This process is repeatedly executed by the drive control unit 36 at a predetermined cycle, for example. In FIG. 11, the same steps as those shown in FIG. 4 are given the same step numbers for the sake of convenience. Further, since the drive control unit 36 according to the present embodiment is hardware, the processing shown in FIG. 11 is actually executed by a logic circuit.

  In this series of processes, when an affirmative determination is made in step S12, the process proceeds to step S32, in which the first switch 76a is turned on and the second switch is selected to select the first threshold voltage V1 as the threshold voltage Vth. 76b is turned off.

  On the other hand, if a negative determination is made in step S12, the process proceeds to step S34, in which the first switch 76a is turned off and the second switch 76b is selected to select the second threshold voltage V2 as the threshold voltage Vth. Turn on the.

  When the processes of steps S32 and S34 are completed, or when a negative determination is made in step S10, the process proceeds to step S18. If an affirmative determination is made in step S18, it is determined that an overcurrent is flowing, and the process proceeds to step S36. In step S36, the soft cutoff switching element 70 is turned on. Thereafter, the process proceeds to step S22.

  If a negative determination is made in step S18, or if the process of step S22 is completed, this series of processes is temporarily terminated.

  Next, FIG. 12 shows an example of the soft blocking process according to the present embodiment. Here, FIG. 12 is a transition of the collector current Ice and the collector-emitter voltage Vce when the switching element S * # is switched to the off state.

  As shown in the figure, the threshold voltage Vth can be changed according to the collector-emitter voltage Vce. For this reason, it is possible to avoid limiting the upper limit value of the collector current that can flow to the switching element S * #, while suppressing an increase in surge voltage when the soft cutoff process is performed.

  According to the present embodiment described above, the following effects can be obtained in addition to the effects obtained in the first embodiment.

  (5) The first switch 76a and the second switch 76b were operated to change the threshold voltage Vth during the period in which the off operation command was issued. In the present embodiment, one of the first switch 76a and the second switch 76b is turned on, and the first and second threshold voltages V1 and V2 are assumed as the threshold voltage Vth. Here, if both the first switch 76a and the second switch 76b are turned on or turned off for some reason, the threshold voltage Vth becomes lower or higher than the initially assumed value. When the threshold voltage Vth is lower than the initially assumed value, the use condition of the switching element S * # is increased by executing the soft shutoff process even though no overcurrent flows through the switching element S * #. There are limited concerns. On the other hand, if the threshold voltage Vth is higher than the initially assumed value, the soft shutoff process is not executed even though an overcurrent actually flows, and the reliability of the switching element S * # may be reduced. is there.

  Here, the collector current does not flow during the period when the OFF operation command is issued. For this reason, according to the present embodiment in which the threshold voltage Vth is changed in the period in which the off operation command is issued, the use condition of the switching element S * # is greatly restricted, or the reliability of the switching element S * # is reduced. Can be avoided.

(Fifth embodiment)
Hereinafter, the fifth embodiment will be described with reference to the drawings with a focus on differences from the fourth embodiment.

  In this embodiment, the method for selecting the threshold voltage Vth is changed.

  FIG. 13 shows a configuration of the drive unit DU according to the present embodiment. In FIG. 13, the same members as those shown in FIG. 10 are given the same reference numerals for the sake of convenience.

  As illustrated, the drive IC 20 includes a memory 66 in which the threshold temperature Sth described in the second embodiment is stored.

  FIG. 14 shows the procedure of the soft shutoff process according to this embodiment. This process is repeatedly executed by the drive control unit 36 at a predetermined cycle, for example. In FIG. 14, the same steps as those shown in FIGS. 7 and 11 are given the same step numbers for the sake of convenience. Further, since the drive control unit 36 according to the present embodiment is hardware, the processing shown in FIG. 14 is actually executed by a logic circuit.

  In this series of processes, when an affirmative determination is made in step S12, the process proceeds to step S24, and the threshold temperature Sth is selected according to the collector-emitter voltage Vce. Thereafter, in step S26, it is determined whether or not the element temperature Sd is equal to or lower than the threshold temperature Sth.

  If an affirmative determination is made in step S26, the threshold voltage Vth is allowed to be the first threshold voltage V1 (increase in the threshold voltage Vth), and the process proceeds to step S32. On the other hand, if a negative determination is made in step S26, the threshold voltage Vth is prohibited from being set to the first threshold voltage V1, and the process proceeds to step S34.

  If a negative determination is made in step S18, or if the process of step S22 is completed, this series of processes is temporarily terminated.

  According to this embodiment described above, in addition to the effect of the fifth embodiment, the same effect as the effect (3) of the second embodiment can be obtained.

(Sixth embodiment)
Hereinafter, the sixth embodiment will be described with reference to the drawings with a focus on differences from the fourth embodiment.

  In this embodiment, the method for selecting the threshold voltage Vth is changed.

  FIG. 15 shows a configuration of the drive unit DU according to the present embodiment. In FIG. 15, the same members as those shown in FIG. 10 are given the same reference numerals for the sake of convenience.

  As illustrated, the drive IC 20 includes the memory 66 described in the fifth embodiment. In this embodiment, the memory 66 stores the threshold voltage Vth in relation to the collector-emitter voltage Vce so that the threshold voltage Vth continuously decreases as the collector-emitter voltage Vce increases. Has been. In the present embodiment, the memory 66 constitutes “threshold storage means”.

  In the present embodiment, the threshold voltage Vth output from the drive control unit 36 is input to the inverting input terminal of the comparator 58.

  FIG. 16 shows the procedure of the soft blocking process according to the present embodiment. This process is repeatedly executed by the drive control unit 36 at a predetermined cycle, for example. In FIG. 16, the same steps as those shown in FIG. 11 are given the same step numbers for the sake of convenience. Since the drive control unit 36 according to the present embodiment is hardware, the processing shown in FIG. 16 is actually executed by a logic circuit.

  In this series of processes, if an affirmative determination is made in step S10, the process proceeds to step S38. In step S38, the threshold voltage Vth corresponding to the collector-emitter voltage Vce is selected from the threshold voltages Vth stored in the memory 66 as the threshold voltage Vth. Specifically, the lower threshold voltage Vth is selected as the collector-emitter voltage Vce is higher. In step S40, the threshold voltage Vth selected in the process of step S38 is output to the comparator 58.

  If a negative determination is made in step S18, or if the process of step S22 is completed, this series of processes is temporarily terminated.

  According to the present embodiment described above, in addition to the effect obtained in the fourth embodiment, the same effect as the effect (4) in the third embodiment can be obtained.

(Other embodiments)
Each of the above embodiments may be modified as follows.

  The “processing means” is not limited to the one that decreases the discharge rate of the gate charge by increasing the resistance value of the soft cutoff path Lcut. For example, in FIG. 8, a power source is connected to a connection point between the seventh terminal T7 and the soft cutoff resistor 68 via a switching element, and the switching element is turned on to supply electric charges to the connection point. Thus, the gate charge discharge rate may be lowered. This utilizes the fact that the gate charge is prevented from being discharged by supplying a charge from the power source to the connection point. In this case, the gate voltage of the device for turning on the soft cutoff switching element 70 may be set to a voltage for driving the soft cutoff switching element 70 in the non-saturated region.

  The “storage unit” is not limited to a unit capable of holding information without power supply. For example, the information is obtained by supplying power on the condition that the drive unit DU has a configuration capable of always supplying power to the storage unit. (For example, a volatile memory) may be used.

  -"Resistance value change means" is not restricted to what was illustrated to the said 3rd Embodiment. For example, as the soft cutoff circuit 50, there are three or more soft cutoff resistors having different resistance values, and the soft cutoff switching connected between each of the soft cutoff resistors and the emitters. When a circuit including an element is employed, these soft cutoff switching elements constitute “resistance value changing means”. Here, as the collector-emitter voltage Vce is higher, only the soft-blocking switching element connected to the soft-blocking resistor having a large resistance value needs to be turned on. That is, in this case, the resistance value Rcut of the soft cutoff path Lcut can be changed in three or more stages. In addition, the selection method of the said resistance value Rcut in this case was illustrated in FIG.

  The method for selecting the threshold voltage Vth is not limited to the method exemplified in the sixth embodiment. For example, as illustrated in FIG. 18, the threshold voltage Vth may be decreased stepwise as the emitter-to-emitter voltage Vce is higher. In FIG. 18, the threshold voltage Vth is selected in four stages.

  -The "current limiting means" is not limited to one that interrupts the flow of collector current. For example, the collector current may be lowered by lowering the gate voltage Vge to a voltage lower than the terminal voltage VH of the constant voltage power supply 22 and higher than the threshold voltage.

  The “current detection means” is not limited to the one provided with the sense resistor 56 that detects the output current of the sense terminal St as the sense voltage Vse. For example, as long as the current flowing through the electrical path from the sense terminal St to the emitter can be detected, other current detection means such as one equipped with a Hall element may be used. In this case, it is desirable to provide a certain resistance to the electrical path so that the sense terminal and the emitter are not short-circuited.

  The “voltage detection means” is not limited to the one provided with the voltage detection unit 64. For example, a sensor that detects a voltage across terminals of the capacitor C that constitutes the boost converter CV may be provided.

  The “temperature detection means” is not limited to the temperature sensitive diode, and may be a thermistor, for example.

  The “driven switching element” is not limited to the IGBT, but may be a MOSFET, for example.

  -The application target of the present invention is not limited to the drive target switching element provided in the inverter for driving the in-vehicle main engine, but is, for example, the drive target switching element provided in the inverter for driving the compressor for air conditioning. May be.

  50 ... Soft cutoff circuit, 58 ... Comparator, 60 ... Power supply, S * # ... Switching element.

Claims (12)

Current detection means (56) for detecting a current flowing between the input / output terminals of the drive target switching element (S * #);
The current flowing between the input and output terminals is forcibly limited by discharging the charge of the switching control terminal of the switching element to be driven on condition that the current detected by the current detection means exceeds a threshold current. Current limiting means (50, 58, 60, 71);
A process of changing the forcible limiting method by the current limiting means so that the higher the applied voltage between the input and output terminals, the greater the degree of suppression of surge voltage that occurs when the current limiting means forcibly limits the surge voltage. Processing means to perform;
A drive circuit for a drive target switching element.   The processing means, as the changing process, performs a process of lowering a discharge rate of charges of the switching control terminal by the current limiting means as the applied voltage between the input and output terminals is higher. The drive circuit of the drive target switching element according to 1. A normal-time discharge path (Ldis) connected to the open / close control terminal and used for normal switching to the OFF state of the drive target switching element;
A discharge switching element (40) provided in the normal-time discharge path and opening and closing the normal-time discharge path;
A soft cutoff path (Lcut) connected to the open / close control terminal and having a resistance value higher than the resistance value of the normal-time discharge path;
A soft shut-off switching element (54a, 54b, 70) provided in the soft shut-off path and opening and closing the soft shut-off path;
Further comprising
The current limiting means forcibly limits the current flowing between the input and output terminals by opening the discharge switching element and closing the soft cutoff switching element,
3. The drive target according to claim 2, wherein the processing means lowers the discharge rate of the charge by increasing the resistance value of the soft cutoff path as the applied voltage between the input and output terminals is higher. Switching element drive circuit. Resistance value changing means (70) operated to change the resistance value of the soft shut-off path continuously or in three or more stages;
The resistance value of the soft cutoff path was stored in relation to the applied voltage between the input and output terminals so that the higher the applied voltage between the input and output terminals, the higher the resistance value of the soft cutoff path. Resistance value storage means (66);
Voltage detection means (64) for detecting an applied voltage between the input and output terminals;
Further comprising
The processing means includes
Comprising resistance value selection means for selecting a resistance value corresponding to the applied voltage detected by the voltage detection means from among the resistance values of the soft cutoff path stored in the resistance value storage means;
4. The drive circuit for a drive target switching element according to claim 3, wherein the resistance value changing unit is operated so that the resistance value of the soft cutoff path is set to the resistance value selected by the resistance value selecting unit. The resistance value changing means includes
Comprising the soft shut-off switching element (70),
5. The drive of a drive target switching element according to claim 4, wherein the resistance value of the soft cutoff path is increased by increasing the on-resistance of the soft cutoff switching element by operating the soft cutoff switching element. circuit. Temperature storage means for storing the temperature of the switching element to be driven in relation to the applied voltage between the input and output terminals so that the temperature of the switching to be driven becomes higher as the applied voltage between the input and output terminals is higher (66)
Voltage detection means (64) for detecting an applied voltage between the input and output terminals;
Temperature selection means for selecting a temperature according to the applied voltage detected by the voltage detection means from among the temperatures stored in the temperature storage means;
Temperature detecting means (SD * #, 62) for detecting the temperature of the switching element;
Permission means for allowing the processing means to increase the discharge rate on condition that the temperature detected by the temperature detection means is equal to or lower than the temperature selected by the temperature selection means;
The drive circuit of the drive target switching element according to claim 2, further comprising:   2. The drive circuit of the drive target switching element according to claim 1, wherein the processing unit performs the process of setting the threshold current to be lower as the applied voltage between the input and output terminals is higher as the process of changing. . Threshold storage means (66) in which the threshold current is stored in relation to the applied voltage between the input / output terminals so that the threshold current decreases as the applied voltage between the input / output terminals increases;
Voltage detection means (64) for detecting an applied voltage between the input and output terminals;
Further comprising
The processing means selects a threshold current corresponding to the applied voltage detected by the voltage detection means from the threshold currents stored in the threshold storage means as the threshold current used in the current limiting means. The drive circuit of the drive target switching element according to claim 7. Temperature storage means for storing the temperature of the switching element to be driven in relation to the applied voltage between the input and output terminals so that the temperature of the switching to be driven becomes higher as the applied voltage between the input and output terminals is higher (66)
Voltage detection means (64) for detecting an applied voltage between the input and output terminals;
Temperature selection means for selecting a temperature according to the applied voltage detected by the voltage detection means from among the temperatures stored in the temperature storage means;
Temperature detecting means (SD * #, 62) for detecting the temperature of the switching element;
Permission means for permitting the processing means to increase the threshold current on condition that the temperature detected by the temperature detection means is equal to or lower than the temperature selected by the temperature selection means;
The drive circuit of the drive target switching element according to claim 7 or 8, further comprising:   The drive target switching element is a series connection body of a high-potential side switching element (S * p) and a low-potential side switching element (S * n) that constitutes an inverter and is connected in parallel to a boost converter (CV). The drive circuit of the drive target switching element according to claim 1, wherein the drive circuit is a drive target switching element.   11. The drive circuit for a drive target switching element according to claim 1, wherein the processing unit changes the restriction method during a period in which the drive target switching element is in an OFF state.   The said current limiting means forcibly interrupts the flow of the current flowing between the input / output terminals as a forced limitation of the current flowing between the input / output terminals. 2. A drive circuit for a drive target switching element according to item 1.