JP2014183680A - Short circuit current protection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a short circuit current protection device that suppresses a malfunction due to a noise while suppressing heat generation of a Zener diode at the time of load short circuit protection.SOLUTION: A comparison voltage value Va is generated using a detection current value Ia of a drain current Id, a second reference voltage value Vref2 is set lower than a first reference voltage value Vref1, a Zener current Izd is limited by a capacitor Ca after a gate end voltage Vg2 is lowered to a Zener voltage Vzd by a gate voltage adjustment part 42 that operates when there occurs a surge current (noise), and the gate end voltage Vg2 is set at 0 [V] through a gate control circuit 54 and a driver 72 when there occurs a load short circuit.

Description

  The present invention relates to a short-circuit current protection device at the time of load short-circuiting of a switching element such as a MOSFET or IGBT used in a power converter that performs conversion between DC power and AC power, for example, a load by converting a DC voltage into an AC voltage. The present invention relates to a short-circuit current protection device for the switching element, which is suitable for application to an inverter or the like that is supplied to the above.

  Conventionally, as shown in Patent Literature 1 and Patent Literature 2, a technology for protecting an excessive short-circuit current from flowing through a switching element constituting a power converter such as an inverter when a load is short-circuited has been disclosed.

  As shown in FIG. 8, the power converter 112 to which the short-circuit current protection device 110 disclosed in Patent Document 1 is applied is between a high level and a low level during normal time (when the load is not short-circuited). A changing gate signal voltage e0 is changed between 0 [V] (reference potential) and a driving voltage (also referred to as a constant voltage) Vcc [V] of the constant voltage power source 106 through complementary transistors 102 and 104. A gate voltage (also referred to as a gate drive voltage) Vg1 (0 [V] or Vcc [V]) is generated and gated to the gate terminals (also referred to as gate input terminals) of the IGBT 114 and the auxiliary IGBT 116 via the resistor 108. By applying a voltage (also referred to as a gate end voltage) Vg2 (0 [V] or Vcc [V]), the IGBT 114 and the auxiliary IGBT 116 are simultaneously turned on / off. And quenching, when on (at turn-on), and is configured to flow a drain current (collector current) Id.

  In this specification, when it is easier to understand by distinguishing between the gate voltage Vg1 and the gate voltage Vg2, the gate voltage Vg1 applied to one end (input end) of the resistor 108 is referred to as the gate drive voltage Vg1. The gate voltage Vg2 applied to the gate terminal (gate input terminal) which is the other end (output terminal) of the resistor 108 is referred to as a gate terminal voltage Vg2.

  The auxiliary IGBT 116 is configured so that an accurate detection current (also referred to as a detection current value) Ia that is a fraction of the drain current Id flowing in the main IGBT 114 in advance flows.

  When the load is short-circuited, the short-circuit current protection device 110 converts the current value of the drain current Id, which is rapidly increased, to the detected current value Ia by the current detection resistor 118 inserted between the emitter terminal of the auxiliary IGBT 116 and the reference potential. Detection is performed with the converted voltage value Va.

  In the short-circuit current protection device 110 according to Patent Document 1, the detected voltage value Va is the sum of the breakdown voltage Vzp of the Zener diode 120 and the base-emitter voltage Vbe of the common-emitter transistor 122 (Vzp + Vbe≈Vzp). The transistor 122 is turned on and the gate terminal voltage Vg2 is clamped to the sum voltage Vzp + Vsat (≈Vzp) of the breakdown voltage Vzp of the Zener diode 120 and the on-voltage Vsat of the transistor 122. As a result, it is presumed that the gate terminal voltage Vg2 is prevented from rising to the drive voltage Vcc, the drain current Id which is a short circuit current is reduced, and the IGBT 114 which is a switching element is protected.

  On the other hand, as shown in FIG. 9, the power converter 212 to which the short-circuit current protection device 210 according to the related art disclosed in Patent Document 2 is applied is 0 [V] at normal time (when the load is not short-circuited). ] (Reference potential) and a driving voltage (also referred to as a constant voltage) Vcc [V] of the constant voltage power supply 106, a gate driving voltage Vg1 (0 [V] or Vcc [V]) that changes between By applying the gate terminal voltage Vg2 (0 [V] or Vcc [V]) to the gate terminal of the IGBT 214 via the device 208, the IGBT 214 is switched on and off, and the drain current Id flows when it is on (turned on). It is configured as follows.

  It is described that the detection current Ia of, for example, 1 / 10,000 of the drain current Id (main current) flowing between the collector and the emitter flows in the sense emitter terminal of the IGBT 214.

  When the load is short-circuited, the short-circuit current protection device 210 converts the detected current value Ia into a voltage obtained by converting the current value of the drain current Id that rapidly increases into the current detection resistor 218 inserted between the emitter terminal and the reference potential. Detect with value Va.

  In the short-circuit current protection device 210 according to Patent Document 2, when the detected voltage value Va becomes the ON voltage Vgson of the protection MOSFET 222 (referred to as a time t3 ′ not shown), the protection MOSFET 222 is used. It is estimated that the ON state (Vds≈0 [V]) is established, and the voltage between the terminals of the capacitor 224 becomes instantaneous to the sense emitter-emitter voltage Vse, which is the gate terminal voltage Vg2 of the IGBT 214.

  Thereafter, the sense emitter-emitter voltage Vse is further estimated to increase toward the gate voltage Vg1 (= Vcc) based on the time constants of the resistor 208 and the capacitor 224.

  By this operation, the increase of the drain current Id is suppressed, and the gate drive voltage Vg1 is stopped by the gate drive circuit 230 at a time after a predetermined time from the load short-circuiting time t3 ′ (time t4 ′ not shown). (State fixed to 0 [V]). As a result, the gate-emitter voltage Vge of the IGBT 214 is decreased, and accordingly, the drain current Id is decreased, the IGBT 214 is turned off, the drain current Id becomes zero value, and the IGBT 214 is assumed to be protected.

JP-A-5-218836 (FIG. 4, [0014] to [0017]) JP 2009-213305 A (FIGS. 2, 3, and 5, [0038] to [0041])

  However, in the short-circuit current protection device 110 according to the prior art disclosed in Patent Document 1, when the gate terminal voltage Vg2 is clamped to the Zener voltage Vzp by the Zener diode 120 during load short-circuit protection, the drive voltage Vcc Since the current (zener current Izp) corresponding to the ability of the constant voltage power source 106 to generate the current and the resistance value of the resistor 108 flows from the constant voltage power source 106 to the Zener diode 120 through the transistor 102 and the resistor 108, There is a problem that a Zener diode 120 formed of a large-sized element with large electric power is required.

  Furthermore, the circuit configuration and elements of the constant voltage power supply 106 and the transistor 102 that generate the drive voltage Vcc also need to have a circuit configuration corresponding to the excessive current. As a result, the entire protection circuit is increased in size and enlarged in specifications. There is a problem of doing.

  If the resistance value of the resistor 108 is increased, the Zener current Izp flowing through the Zener diode 120 at the time of load short-circuit protection can be suppressed. However, the resistance value of the resistor 108 is the resistance value of the IGBTs 114 and 116 that are switching elements. When the switching characteristic is set to a value larger than a value that can be secured, the switching time (the transition time during which the IGBTs 114 and 116 transition from the on state to the off state or from the off state to the on state) becomes long. There are limitations.

  Even if a resistor is inserted in series with the transistor 122 and the Zener diode 120, a delay occurs when the load is short-circuited, and the IGBTs 114 and 116 are damaged.

  In addition, the breakdown voltage Vzp of the Zener diode 120 varies, and there is a problem that it is difficult to perform protection control with a constant detection current value Ia.

  On the other hand, also in the short-circuit current protection device 210 of the prior art according to Patent Document 2, the on-voltage (referred to as the gate threshold voltage Vgsth) of the protection MOSFET 222 varies, and protection control is performed at a constant detection current value Ia. Therefore, there is a problem that malfunction due to noise such as surge current at the time of switching is likely to occur.

  The present invention has been made in consideration of such various problems, and is capable of suppressing malfunction due to noise while suppressing heat generation of a protective Zener diode during protection. The purpose is to provide.

  In the claims and this [Means for Solving the Problems], for convenience of understanding, the current value in consideration of the characteristics of an N-type switching element such as an NMOSFET or an NPN IGBT as a switching element. Although the threshold size is described, it is obvious that the scope of the claims includes the case where it is applied to the characteristics of the P-type switching element, as understood by understanding the numerical value as an absolute value. Absent.

  The short-circuit current protection device according to the present invention is a short-circuit current protection device for a power converter including a switching element, wherein the switching element is turned on by applying a predetermined drive voltage as a gate voltage to the gate input terminal of the switching element. And a gate control circuit for controlling the turn-off, a current detection unit for detecting a current value flowing through the switching element, and detecting that the current value has exceeded a first threshold, and a first time after the detection A protection circuit for cutting off the application of the gate voltage by the gate control circuit; and detecting that the current value exceeds a second threshold value that is smaller than the first threshold value, and more than the first time after detection After a short second time, the gate voltage is reduced below the driving voltage, and the current value exceeds the second threshold value. If it falls below the second threshold after it is characterized by and a gate voltage adjusting unit which applies the driving voltage.

  For the convenience of understanding, when it is assumed that the gate voltage adjusting unit according to the present invention does not exist, the first threshold value set in the protection circuit is relatively high and does not exceed by noise such as surge at turn-on. If it is not set to a large value, the noise is erroneously detected as a load short circuit, and the performance of a switching element utilizing device such as an inverter is deteriorated. On the other hand, if the first threshold value set in the protection circuit is set to a large value in order to prevent erroneous detection due to noise, the time taken until the gate voltage is cut off increases, and therefore stress (electrical) applied to the switching element is increased. Damage) is increased, and as a result, the life of the switching element is shortened.

  Therefore, the present invention includes a gate voltage adjustment unit in addition to the protection circuit. The gate voltage adjustment unit detects that the value of the current flowing through the switching element has exceeded a second threshold value that is smaller than the first threshold value, which is an operation start condition of the protection circuit. When the gate voltage is reduced below the drive voltage after a time shorter than the first time during which the application of the gate voltage is cut off, and the current value exceeds the second threshold value and then falls below the second threshold value In this configuration, the drive voltage is applied, and this configuration can prevent the protection circuit from being completely activated due to noise generation (normal surge generation).

  More specifically, the gate voltage adjustment unit has one end connected to the gate input terminal side and the other end connected to the reference potential side, and the current value is smaller than the first threshold value. You may comprise so that the switch part which will be in a conduction | electrical_connection state when it exceeds, and the capacitor | condenser and Zener diode which were connected in series between the said switch part and the said gate input terminal may be provided.

  According to this configuration, when the value of the current flowing through the switching element exceeds the second threshold value set to a value smaller than the first threshold value, the gate voltage adjustment unit operates and the switch unit becomes conductive. First, the gate voltage (gate end voltage) input to the gate input terminal is instantaneously reduced to the breakdown voltage of the Zener diode.

  Therefore, the current flowing through the switching element is instantaneously limited due to the reduction of the gate end voltage to the breakdown voltage, and an excessive current is generated in the switching element even in a state where a short circuit such as a load short circuit has occurred or not. Is suppressed from flowing.

  As described above, the gate voltage adjusting unit is connected in series between the switch unit and the gate input terminal, the switch unit having one end connected to the gate input terminal side and the other end connected to the reference potential side. Since it has a relatively simple configuration including a capacitor and a Zener diode, when the current value exceeds the second threshold value, the gate terminal voltage can be instantaneously reduced to the breakdown voltage of the Zener diode (response) Short time and quick response).

  In addition, when the current value temporarily exceeds the second threshold value, that is, when a load short circuit has not occurred, for example, when the current value temporarily increases due to a surge during a normal turn-on operation, for example. Although the gate terminal voltage is temporarily reduced by the gate voltage adjustment unit, the normal gate voltage is quickly increased in response to the current value falling below the second threshold value which is smaller than the first threshold value. Since the voltage is applied to the gate input terminal, normal switching operation can be continued without erroneously detecting a load short circuit. In this case, the protection circuit does not operate.

  Further, when the current value exceeds the first threshold value set to a value larger than the second threshold value, it is assumed that a load short-circuit has occurred, and the protection circuit is activated. As a result, the current flowing through the switching element is also cut off, the operation of the switching element is stopped, and the switching element is protected.

  As described above, the first threshold value set in the protection circuit is set to a value larger than the second threshold value set in the gate voltage adjustment unit in order to prevent erroneous detection of a load short circuit. As a result, the response time is longer than that of the gate voltage adjustment unit (response is delayed). That is, a delay time (the first time) occurs from when the current value exceeds the first threshold value until the gate voltage cut-off operation starts.

  For this reason, when the application of the gate voltage is cut off only by the protection circuit when the load is short-circuited, the gate end voltage by the normal gate voltage is applied during the time until the gate voltage is cut off. However, according to the present invention, when the load is short-circuited, the response time is relatively short (second time), and the gate voltage adjustment unit that operates at high speed is provided. First, after reducing the gate end voltage, the gate voltage can be cut off by the protection circuit when the current value becomes large enough to determine the load short circuit (when the current value exceeds the first threshold value). It is possible to suppress erroneous detection of a load short circuit while reducing a current value (energy) flowing until the switching element stops at the time of a short circuit.

  Furthermore, the gate voltage adjustment unit includes a capacitor and a Zener diode connected between the switch unit and the gate input terminal, so that when the current value exceeds the second threshold value, the gate voltage adjustment unit is input to the gate input terminal. First, the gate terminal voltage is lowered to the breakdown voltage of the Zener diode, and then the current flowing through the Zener diode is reduced as the capacitor is charged. Therefore, heat generation of the Zener diode can be reduced. Therefore, compared with the case where the zener diode is configured only, the heat generated by the zener diode is reduced, and a small element having a small element size can be employed as the zener diode.

  The gate terminal voltage input to the gate input terminal will gradually increase as the capacitor is charged, but when the load short circuit is established, the application of the gate voltage is cut off by the protection circuit. The current flowing through the switching element can be interrupted before the current flowing through the element increases.

  In this case, the protection circuit flows to the switching element when the gate voltage lowered by the Zener diode of the gate voltage adjusting unit is increased by charging the capacitor at the time of short circuit (load short circuit). It is provided in order to reliably cut off the gate voltage (the gate drive voltage) before the current value rises to a deterioration start limit current value or a current value that allows a certain degree of deterioration.

  Further, the protection circuit and the gate voltage adjustment unit include first and second comparators that use the first threshold value and the second threshold value as a first reference voltage value and a second reference voltage value, respectively, and the current value In order to compare the threshold and the current flowing through the switching element to the resistor, the voltage across the resistor is used as a comparison voltage value, and when the comparison voltage value exceeds the second reference voltage value, The protection circuit is configured when the switch unit is turned on by a transition output of the second comparator configuring the gate voltage adjustment unit, and then the comparison voltage value exceeds the first reference voltage value. By adopting a configuration in which the application of the gate voltage (the gate drive voltage) is cut off by the transition output of the first comparator, while avoiding erroneous detection of noise or the like by the gate voltage adjustment unit as a load short circuit Preliminary high-speed protection that protects the switching element and protection of the switching element when the load is short-circuited by the protection circuit are set with the second and first reference voltage values corresponding to a fixed reference current value, respectively. Each can be started by utilizing the second and first comparators.

  According to this invention, since the capacitor is connected in series with the protective Zener diode, the heat generation of the protective Zener diode at the time of protection is suppressed and compared with the threshold value (first threshold value) at which the protective circuit operates. A malfunction caused by noise can be suppressed by the gate voltage adjustment unit having a threshold value (second threshold value) set to a relatively small value.

It is a lineblock diagram of an electric vehicle to which a short circuit current protection device concerning this embodiment was applied. It is a detailed block diagram of the short circuit current protection apparatus which concerns on this embodiment. It is a flowchart with which operation | movement description of the short circuit current protection apparatus which concerns on this embodiment is provided. It is a timing chart used for operation | movement description of the short circuit current protection apparatus which concerns on this embodiment. FIG. 5 is a timing chart illustrating a part of a period including a short-circuit current protection period in an expanded manner in the timing chart of FIG. 4; It is typical explanatory drawing of the electric power reduction of a switching element and a Zener diode. It is a detailed block diagram of the short circuit current protection apparatus which concerns on other embodiment. It is a block diagram of the short circuit current protection apparatus which concerns on the prior art disclosed by patent document 1. FIG. It is a block diagram of the short circuit current protection apparatus which concerns on the prior art disclosed by patent document 2. FIG.

  Hereinafter, preferred embodiments of the short-circuit current protection device according to the present invention will be described in detail with reference to the accompanying drawings.

  In the drawings to be referred to below, components corresponding to those shown in FIGS. 8 and 9 are given the same reference numerals, and detailed description thereof is omitted.

  FIG. 1 shows a configuration of an electric vehicle 12 to which a short-circuit current protection device 10 according to this embodiment is applied.

  The electric vehicle 12 basically includes a high-voltage battery 14 and a voltage converter that converts a direct-current battery voltage Vbat of, for example, several hundred [V], which is a power supply voltage of the battery 14, into a three-phase AC voltage. As an inverter 16, a drive motor 18 driven by the AC voltage, and a gate drive unit 20 constituted by an ECU (Electronic Control Unit) that controls and drives these elements. The rotating shaft of the drive motor 18 is connected to the wheels via a transmission (not shown).

  The electric vehicle 12 includes a drive motor 18 as a power source and at least a battery 14 as a power resource, so-called EV, HEV (hybrid vehicle), PHEV (plug-in hybrid vehicle), and FCV (fuel cell vehicle). ) Etc. are included. In addition, when the electric vehicle 12 is a range extended EV, as is well known, an internal combustion engine and a generator are used. The gate drive unit 20 according to this embodiment includes an AC voltage generated by the generator. Can also be applied to inverters that convert DC to DC voltage.

  As the drive motor 18, a U-phase, V-phase, and W-phase coil 18u, 18v, 18w as a stator is connected in a Y shape and a permanent magnet (PM) is embedded in the circumferential direction. The PM motor (permanent magnet synchronous motor) provided is used.

  During power running, the electric power of the battery 14 is supplied to the drive motor 18 through the fuse 22, the electromagnetic relay 24, the harness 26, the inverter 16, and the harness (bus bar) 30.

  Further, during regeneration such as during deceleration, the regenerative power of the drive motor 18 is AC / DC converted through the inverter 16 to charge the battery 14.

  A voltage sensor 32 for detecting the battery voltage Vbat and a smoothing capacitor 34 are connected between the positive electrode P and the negative electrode N (reference potential) of the battery 14, and the current sensor 35 (voltage sensor) is connected to the battery on the negative electrode N side. A shunt resistor for detecting the current Ibat is connected.

  The inverter 16 includes switching elements Q1 to Q6, each of which is a power device, and diodes D1 to D6 connected in reverse directions to the switching elements Q1 to Q6, respectively, connected in a three-phase full bridge configuration. Phase switching device Q1 and diode D1, switching device Q2 and diode D2, switching device Q3 and diode D3, switching device Q4 and diode D4, switching device Q5 and diode D5, switching device The midpoints of Q6 and diode D6 are connected to the three-phase UVW-phase U-phase coil 18u, V-phase coil 18v, and W-phase coil 18v of the drive motor 18.

  Switching elements Q1 to Q6 employ MOSFETs, but may be IGBTs or other switching elements.

  As is well known, the switching elements Q1 to Q6 are switched on and off (turned on and off) based on a PWM (pulse width modulation) signal generated by the gate drive unit 20, and energized time (on time) within a predetermined period (predetermined time). ) Is controlled.

  FIG. 2 shows a detailed configuration of the short-circuit current protection device 10 that drives and protects one switching element Q in the gate drive unit 20 that controls the switching elements Q1 to Q6 based on the PWM signal. In practice, the gate drive unit 20 shown in FIG. 2 is prepared for each of the switching elements Q1 to Q6. Here, for convenience of understanding and avoidance of complexity, only one switching element Q is provided. A circuit configuration diagram is drawn.

  Further, each ground (GND) drawn in FIG. 2 is for convenience of understanding, and in fact, a constant voltage power supply (not shown) similar to the constant voltage power supply 106 shown in FIGS. 8 and 9 is used. This means a reference potential (generally expressed as Vee or the like; Vcc> Vee) with respect to a constant voltage Vcc (also referred to as drive voltage Vcc) generated from.

  The reference potentials of the lower arm switching elements Q4, Q5, and Q6 are set to, for example, the negative electrode side of the battery 14 (floating from the chassis ground in the example of FIG. 1), and the upper arm switching elements Q1, Q2 are set. , Q3 is set to the High side potential of the switching elements Q4, Q5, Q6 of the lower arm.

  The gate drive unit 20 includes a protection circuit 41 and a gate voltage adjustment unit 42 that constitute the short-circuit current protection device 10.

  As shown in FIG. 2, the protection circuit 41 includes a first comparator 51 and a gate control circuit 54 including a latch circuit 55. The first comparator 51 compares the comparison voltage value Va with the first reference voltage value Vref1 that is the first threshold value, and when the comparison voltage value Va becomes a voltage exceeding the first reference voltage value Vref1, A voltage comparator 61 such as a comparator including a hysteresis function is provided, which outputs a protection signal (comparison result signal) Sp1 that changes from level to high level to a latch circuit 55 that constitutes the gate control circuit.

  The first reference voltage value Vref1 is set to an accurate value obtained by resistively dividing a constant voltage Vcc (also referred to as a drive voltage Vcc) generated from a constant voltage power source (not shown) with a precise resistor. The first reference voltage Vref1 may be generated using a reference voltage generating integrated circuit. In this embodiment, the constant voltage Vcc is set to several [V] to several tens [V] (Vcc = several [V] to several tens [V]) as an example. In this case, the first reference voltage value Vref1 is set to a value for detecting the first excessive current value Idov1 (see FIG. 4) of the drain current Id in order to detect a load short circuit.

  In FIG. 2, a gate control circuit 54 outputs a PWM signal generated by a microcomputer (not shown) through an appropriate buffer circuit and filter circuit. The PWM signal output from the gate control circuit 54 is converted into a gate voltage (gate drive voltage) Vg1 that takes a binary value of 0 [V] or the drive voltage Vcc through the driver 72, and further, the resistor Rg (the resistance value is also Rg). Is applied to the gate terminal (gate input terminal) of the switching element Q as a gate voltage (gate end voltage) Vg2.

  When the gate voltage adjustment unit 42 does not detect an excessive current value Ia, which will be described later, in other words, the normal gate voltage Vg2 when no noise such as a short circuit or surge voltage is generated in the load is It is approximately equal to the voltage Vg1.

  The gate voltage adjustment unit 42 includes a second comparator 52 and a gate voltage limiting circuit 56 that limits the gate voltage (gate end voltage) Vg2 of the switching element Q.

  The gate voltage limiting circuit 56 is a Zener having a breakdown voltage (Zener voltage) Vzd, which is connected in series between the switch unit SWa formed of MOSFET, the drain terminal of the switch unit SWa, and the gate terminal of the switching element Q. A diode ZD and a parallel circuit of a capacitor Ca and a resistor Rd are provided. In addition to the MOSFET, an appropriate switching element such as an IGBT or a transistor can be used for the switch unit SWa.

  In this embodiment, a Zener diode ZD having a nominal value of several volts [V] (Vzd = several volts [V] to several tens of volts [V]) is used as an example of the breakdown voltage Vzd of the Zener diode ZD. The resistor Rd is a discharge resistor. For example, when the protection circuit 41 operates on the order of microseconds, the resistor Rd discharges the electric charge accumulated in the capacitor Ca on the order of 100 to 1000 times, for example, milliseconds. Set to

  The switching element Q includes a drain terminal into which a drain current Id flows, a gate terminal to which a gate voltage Vg2 is applied, a source terminal connected to a ground (GND) that is a reference potential, and a drain terminal and a source terminal. A diode D and a sense source terminal connected in the opposite direction are provided. The sense source terminal is connected to the resistor Ra, one end of which is connected to the reference potential, and the input terminals of the protection circuit 41 and the gate voltage adjusting unit 42.

  From the sense source terminal of the switching element Q, exactly a fraction of the drain current Id flows out as the detection current Ia. The current value of the detection current Ia (also referred to as Ia) causes a voltage drop in the resistor Ra (resistance value is also assumed to be Ra) that forms the gate driving unit 20 with a small error, and the detection current value Ia A proportional voltage value (also referred to as a comparison voltage value) Va is generated. The resistor Ra operates as a current detection unit for the drain current Id.

  If the switching element Q does not include a sense source terminal, a small resistance resistor or a current sensor is inserted between the source terminal of the switching element Q and the ground (virtual reference potential). May be.

  The second comparator 52 of the gate voltage adjustment unit 42 compares the comparison voltage value Va with the second reference voltage value Vref2 that is the second threshold, and determines that the comparison voltage value Va exceeds the second reference voltage value Vref2. In this case, the switch signal (comparison result signal) Sp2 that transitions from the low level to the high level is output to the gate terminal of the switch unit SWa including the switching elements (here, MOSFETs) constituting the gate voltage limiting circuit 56. For example, a voltage comparator 62 such as a comparator having a hysteresis function is provided. The second reference voltage value Vref2 is also set to an accurate value obtained by dividing the constant voltage Vcc with a precise resistor. In this case, the second reference voltage value Vref2 is set to a value for detecting the second overcurrent value Idov2 (Idov2 <Idov1) (see FIG. 4) corresponding to the surge current of the drain current Id.

  As described above, when the gate voltage adjustment unit 42 does not detect an excessive current value Ia, in other words, during normal times when noise such as a short circuit or a surge voltage is not generated in the load, the second comparator 52. The switch unit SWa is turned off by the low-level switch signal Sp2 that is the output signal of. For this reason, the gate voltage adjustment unit 42 is in an open circuit state with respect to the gate terminal of the switching element Q.

  Here, although there is a variation in the gate-source on-voltage of the switch unit SWa that is a MOSFET, the high level output from the second comparator 52 that operates correctly (inverts) at the second reference voltage value Vref2 (inverted). This value can be set to a voltage more than twice the gate-source on-voltage of the switch unit SWa.), So that the switch unit SWa has the comparison voltage value Va of the second reference voltage. When the value Vref2 is exceeded, an instantaneous transition is made from the off state to the on state (the drain-source voltage is approximately zero).

  When the switch unit SWa transitions to the ON state, the gate drive voltage Vg1 is Vg1 = Vcc, so the gate terminal voltage Vg2 is clamped to the breakdown voltage Vzd of the Zener diode ZD, and then the gate terminal voltage Vg2 is The capacitor Ca rises by being charged with a time constant Ca × Rg toward the driving voltage Vcc through the resistor Rg. When the voltage between the terminals of the capacitor Ca is charged (increased) from the reference potential 0 [V] to the voltage (Vcc−Vzd), the Zener diode ZD changes from the breakdown state to the off state, and the gate voltage adjustment unit 42 is switched. It is electrically disconnected from the gate terminal of the element Q (opened).

  As described above, the gate drive unit 20 is configured by an ECU. The ECU includes a computer, and the CPU realizes various functions by executing programs stored in a memory such as a ROM based on various inputs. Although it operates also as a functional unit (functional means), these functions can also be realized by hardware. In practice, in this embodiment, the portion of the short-circuit current protection device 10 is configured substantially by hardware. The gate drive unit 20 can be configured by a drive circuit, a control circuit, or the like independent of the ECU, instead of the ECU.

  In this embodiment, the gate drive unit 20 functions as the short circuit current protection device 10 including the protection circuit 41 and the gate voltage adjustment unit 42, and similarly to the normal electric vehicle 12, the accelerator pedal operation, the shift operation, and the like. The drive motor 18 generates a PWM signal having a duty corresponding to the command voltage and the battery voltage Vbat to be driven at a desired rotational speed and a desired torque, and performs feedback control.

  The operation of the short-circuit current protection device 10 according to this embodiment that is basically configured and operates as described above will be described with reference to the flowchart of FIG. 3 and the timing chart of FIG. Note that a CPU (not shown) of the gate drive unit 20 executes the program according to the flowchart.

  When a PWM signal created in a normal (known) manner is input to the gate control circuit 54 in step S1, the gate control circuit 54 detects an edge of the PWM signal in step S2. Note that the waveform of the PWM signal is different from the waveform of the gate drive voltage Vg1 and the gate end voltage Vg2 in normal times, and the amplitude in which the on (ON, high level) and off (OFF, low level) timings are synchronized. is there.

  In this case, as shown in the flowchart, the edge detection result in step S2 is either a rising edge, a falling edge, or maintenance (not an edge but a voltage does not change).

  In step S2, for example, when it is determined that it is a rising edge as shown at time t1, in step S3, the switching element is output by outputting the gate drive voltage Vg1 that transitions from the low level to the high level. A gate terminal voltage Vg2 (Vg2 = Vcc [V]) that changes from a low level to a high level is applied to the gate terminal of Q.

  For example, when the gate terminal voltage Vg2 transitioning from the low level to the high level is applied to the gate terminal of the switching element Q5 of the lower arm element shown in FIG. The switching device Q1, the U-phase coil 18u of the drive motor 18 and the V-phase are turned on when the gate end voltage Vg2 which is shifted from the low level to the high level is applied and turned on and the battery current Ibat from the battery 14 is turned on. It flows through the coil 18v and the switching element Q5 that is turned on (the other switching elements Q2, Q3, Q4, and Q6 are off).

  In practice, the drain current Id flowing through the switching elements Q1 and Q5 at this time rises with an inclination depending on the inductance of the U-phase coil 18u and the V-phase coil 18v, as shown between the time points t1 and t2 in FIG. Then, a peak value surge (surge voltage) is generated at time t2, and then gradually increases.

  Next, in step S4, in practice, at the time t1, the gate voltage adjustment unit 42 determines whether or not the drain current Id exceeds the second overcurrent value Idov2, and the detected voltage value Va is the second reference voltage value. Detection is made based on whether or not Vref2 is exceeded (Va> Vref2).

  At time t1 to t2, it has not exceeded. In this case, the determination in step S4 is negative (step S4: NO), the process returns to step S1, and step S1 → step S2: maintenance → step S4: NO is repeated every minute time until time t3.

  Next, when it is determined in step S2 corresponding to the time point t3 that the PWM signal is a falling edge, in step S5, the gate drive voltage Vg1 that transitions from the high level to the low level is output. A gate terminal voltage Vg2 (Vg2 = 0 [V]) that changes from a high level to a low level is applied to the gate terminal of the switching element Q.

  In this case, the switching elements Q1 and Q5 are turned off at time t3 by the gate terminal voltage Vg2 of the switching element Q5 of the lower arm element and the gate terminal voltage Vg2 of the switching element Q1 of the upper arm element synchronized with this. To be.

  After the process of step S5, from time t3 to time t4, step S1 → step S2: maintenance → step S4: NO → step S1 is repeated every minute time.

  Next, when it is determined in step S2 corresponding to time point t4 that it is a rising edge, in step S3, the gate control circuit 54 outputs the gate drive voltage Vg1 that transitions from the low level to the high level. Thus, the gate terminal voltage Vg2 (Vg2 = Vcc [V]) that changes from the low level to the high level is applied to the gate terminals of the switching elements Q2 and Q6.

  At this time, the battery current Ibat from the battery 14 flows through the switching element Q2 in the turn-on state, the V-phase coil 18v, the W-phase coil 18w of the drive motor 18, and the switching element Q6 in the turn-on state (the other switching elements Q1, Q3 , Q4, and Q5 are off.)

  Then, when the drain current Id flowing through the switching element Q6 (referred to as the switching element Q in FIG. 2) exceeds the second excessive current value Idv2 due to the generated surge voltage at the subsequent time point t5, the detection voltage in step S4 Since the value Va is designed to exceed the second reference voltage value Vref2 (Va> Vref2), the second comparator 52 (voltage comparator 62) of the gate voltage adjustment unit 42 operates (inverts) (step) S4: YES).

  At time points t5 to t6 when the voltage comparator 62 is inverted, a gate voltage limiting (reducing) process by the gate voltage adjusting unit 42 in step S6 is executed.

  In this gate voltage limiting process, when the detected current value Ia rises to a value corresponding to the second excessive current value Idov2, Va> Vref2 is established and the second comparator 52 operates (inverts), and its output Is switched from the low level to the high level, the switch unit SWa is turned on, the Zener current Izd flows through the Zener diode ZD, the Zener diode ZD becomes the region of the breakdown voltage Vzd, and the switching element Q The gate terminal voltage Vg2 applied to the gate terminal is lowered to the breakdown voltage Vzd (see FIG. 4). As a result, the drain current Id exceeding the second excessive current value Idov2 is avoided, and the stress applied to the switching element Q is minimized so as not to affect the life of the switching element Q.

  In this case, between the input end of the V-phase coil 18v driven by the switching elements Q2 and Q6 and the input end of the W-phase coil 18w (between the switching elements Q2 and Q5 and the midpoint of the switching elements Q3 and Q6), Since no short circuit (load short circuit) has occurred, when the surge voltage (surge current) disappears at time t5 + Δt (Δt is a minute time), the detected current value Ia is determined to be the second overcurrent value Idov2 in the determination process of step S7. Since the first excessive current value Idov1 that detects the occurrence of a larger load short-circuit is not reached, the determination in step S7 (Va> Vref1) becomes negative (step S7: NO), and the process returns to step S1.

  Thereafter, from time t5 to time t8, step S1 → step S2: maintenance → step S4: NO is repeated every minute time. Note that the element temperature Tzd of the Zener diode ZD increases from the ambient temperature between the time points t5 and t7.

  Next, from time t8 to t10, step S1 → step S2: maintenance → step S4: NO is repeated every minute time, but at time t9 between time t8 and time t10, the W-phase coil 18w and the U-phase coil It is assumed that a short circuit (load short circuit) has occurred at the input end of the 18 u drive motor 18.

  In this case, in step S2 corresponding to time t10, the gate control circuit 54 determines that the PWM signal is a rising edge, and in step S3, outputs the gate drive voltage Vg1 that transitions from the low level to the high level. Thus, the gate terminal voltage Vg2 (Vg2 = Vcc [V]) that changes from the low level to the high level is applied to the gate terminals of the switching elements Q3 and Q4.

  At this time, the battery current Ibat from the battery 14 passes through the switching element Q3 in the turn-on state, passes through the short circuit (bypassing the W-phase coil 18w and the U-phase coil 18u of the drive motor 18), and passes through the switching element Q4 in the turn-on state. Flowing.

  In this case, the determination in step S4 corresponding to time t11 (Va> Vref2) becomes affirmative, and the gate terminal voltage Vg2 is reduced to the breakdown voltage Vzd of the Zener diode ZD by the operation of the gate voltage adjustment unit 42. Since the current Id becomes a short-circuit current, the degree of increase is suppressed after time t11 but increases.

  Then, since the detected current value Ia in step S7 corresponding to the time point t11 ′ exceeds the first excessive current value Idov1 that is larger than the second excessive current value Idov2, the determination in step S7 (Va> Vref1) is positive (step S7). : YES), and load short-circuit protection processing is performed in step S5.

  That is, when the detected voltage value Va exceeds the first reference voltage value Vref1 at time t11 ′, the first comparator 51 of the protection circuit 41 operates (inverts), and the protection signal Sp1 changes from low level to high level (active). Level).

  As a result, the latch circuit 55 operates irreversibly, and the gate control circuit 54 forcibly changes the gate drive voltage Vg1 from the high level drive voltage Vcc to the low level reference potential (= 0 [V]). Is output to the driver 72 at time t12 after a predetermined delay time Td has elapsed.

  As a result, the capacitor Ca is charged from the time t11 to the time t12, the gate terminal voltage Vg2 increases, and the drain current Id flowing through the switching element Q becomes a deterioration start limit current value or a current value Idvlimit that allows a certain degree of deterioration. Before rising to the low level, the gate drive voltage Vg1 and the gate end voltage Vg2 are set to the low level 0 [V]. The deterioration start limit current value is a predetermined threshold current value that shortens the life of the switching element Q when the current value is exceeded. The current value Idvlimit that allows a certain level of deterioration is larger than the deterioration start limit current value and starts to deteriorate. In other words, the life is shortened, but even if the life is shortened, for example, a short circuit The life of a product to which the current protection device 10 is applied, in this embodiment, an acceptable life or the like that is equal to or higher than the product life of the electric vehicle 12.

  Due to the low level 0 [V] output of the gate drive voltage Vg1 of the driver 72, the gate end voltage Vg2 is simultaneously changed from the substantially Zener voltage Vzd to the low level 0 [V], and the switching elements Q3 and Q4 are turned off, so-called. Since the cut-off state (open state) is set, the drain current Id corresponding to the short-circuit current decreases after the time t12 and becomes zero at the time t13. If necessary, the electromagnetic current is generated by the relay control signal Sr after the time t12. The relay 24 is changed from the closed state to the open state. For this reason, the temperature rise of the element temperature Tzd of the Zener diode ZD is eliminated at time t14.

[Summary of Embodiment]
As described above, in the short circuit current protection device 10 for the inverter 16 that is the power converter including the switching element Q according to the above-described embodiment, the gate input terminal of the switching element Q has a predetermined drive voltage Vg1 as the gate voltage Vg2. A gate control circuit 54 that controls turn-on and turn-off of the switching element Q by applying (0 [V], Vcc [V]), and current detection that detects a current value Id flowing through the switching element Q as a comparison voltage value Va And detecting that the comparison voltage value Va corresponding to the current value Id exceeds the first threshold value Vref1 (time point t11 ′) and a first time after the detection (time point t12) A protection circuit 41 for cutting off the application of the gate voltage Vg1 (Vg2) by the gate control circuit 54, and the current value I It is detected that the comparison voltage value Va corresponding to 1 exceeds the second threshold value Vref2 that is smaller than the first threshold value Vref1 (time point t5), and the first time after the detection (time between time points t11 ′ to t12) After a shorter second time (immediately after the time point t5 ′), the gate voltage Vg2 is reduced from the drive voltage Vg1 (set to Vzd), and the comparison voltage value Va corresponding to the current value Id is the second threshold value. And a gate voltage adjusting unit 42 that applies the drive voltage Vg1 when the voltage falls below Vref2 (time t6). With this configuration, it is possible to avoid that the protection circuit 41 is completely activated due to noise generation (normal surge generation).

  In this way, the switching elements Q (Q1 to Q6) constituting the inverter 16 are protected from the load short circuit, and the heat generation of the Zener diode ZD during the load short circuit protection is suppressed (described in detail later), but due to noise. Malfunctions can be suppressed.

  That is, the comparison voltage value Va, which is a voltage drop, is generated in the resistor Ra by the detected current value Ia of the drain current Id, and the second reference voltage value Vref2 is set to a value lower than the first reference voltage value Vref1, and the surge current After the gate voltage Vg2 is lowered to the zener voltage Vzd by the gate voltage adjustment unit 42 having the second comparator 52 that is inverted and activated when (noise) occurs, the zener current Izd is limited by charging the capacitor Ca. When a load short circuit occurs, the gate voltage Vg2 is set to 0 [V] through the driver 72 by the first comparator 51 and the gate control circuit 54, thereby preventing a malfunction of the switching element Q due to noise, and a Zener diode The heat generation of ZD is suppressed, and the switching element Q is protected from destruction when the load is short-circuited.

  More specifically, the short-circuit current protection device 10 includes a gate control circuit 54 that controls turn-on and turn-off of the switching element Q by applying a predetermined gate terminal voltage Vg2 to the gate input terminal of the switching element Q, and the switching element Q A resistor Ra for generating a voltage drop as a current detection unit that detects a current value Ia that is proportional to a drain current Id that is a current value that flows through the capacitor, and a comparison voltage value Va corresponding to the predetermined current value Ia as a first threshold value When the first reference voltage value Vref1 is exceeded, the protection circuit 41 that cuts off the application of the gate drive voltage Vg1 by the gate control circuit 54 and the gate end voltage Vg2 are reduced based on the current value Ia (in this embodiment, And a gate voltage adjusting unit 42 that is reduced from Vcc to Vzd.

  The gate voltage adjustment unit 42 has one end connected to the gate input terminal side and the other end connected to the reference potential side, and a comparison voltage value Va corresponding to the current value Ia is a first threshold value as the first threshold value. A switch unit SWa that becomes conductive when it exceeds a second reference voltage value Vref2 (Vref2 <Vref1) as a second threshold value smaller than the reference voltage value Vref1, and is connected in series between the switch unit SWa and the gate input terminal. And a connected capacitor Ca and a Zener diode ZD.

  Here, the timing chart of FIG. 4 shown in FIG. 5 will be described with reference to a timing chart in which the period including the short-circuit current protection period is partially deformed and enlarged.

  According to the configuration of the short-circuit current protection device 10 described above, a load short-circuit occurs at time t9, and the detection voltage value Va based on the detection current value Ia corresponding to the drain current Id flowing through the switching element Q is the first reference voltage value Vref1. When the second reference voltage value Vref2 set to a smaller value is exceeded (time t11 in FIG. 5), the gate voltage adjustment unit 42 is activated and the switch signal Sp2 changes from the low level to the high level. When SWa is turned on, the gate terminal voltage Vg2 input to the gate input terminal of the switching element Q is instantaneously reduced to the breakdown voltage Vzd of the Zener diode ZD.

  Due to the decrease of the gate end voltage Vg2 to the breakdown voltage Vzd, the drain current Id flowing through the switching element Q does not rise like the drain current Id indicated by the two-dot chain line when the short-circuit current protection device 10 is not present. The rise is limited like a drain current Id indicated by a one-dot chain line.

  When the detected voltage value Va exceeds the first reference voltage value Vref1 at time t11 ′, the first comparator 51 operates (inverts), and the protection signal Sp1 changes from the low level to the high level (active level).

  As a result, the latch circuit 55 operates irreversibly, and the gate control circuit 54 forcibly changes the gate drive voltage Vg1 from the high level drive voltage Vcc to the low level reference potential (= 0 [V]). Is output to the driver 72 at a time point t12 after a predetermined delay time Td has elapsed (see the waveform of protection control by the gate control circuit 54 in FIG. 5).

  As a result, at time t12, the gate voltages Vg1 and Vg2 transition to a low level, the switching element Q is cut off, and the drain current Id due to a load short-circuit decreases rapidly. Until the drain current Id becomes zero at time t12 to t14, the protection signal Sp1 becomes low level at time t12 ′, and the switch signal Sp2 becomes low level at time t13, but at the previous time t12. Since the irreversible protection control is applied by the gate control circuit 54 constituting the protection circuit 41, there is no problem.

  In this way, even in a state where a short circuit such as a load short circuit occurs, the drain current Id flowing through the switching element Q is limited to a deterioration start limit current value or a value equal to or less than a current value Idolimit that allows a certain level of deterioration. Therefore, it is possible to suppress the excessive drain current Id from leading to life deterioration / destruction.

  That is, the gate voltage adjusting unit 42 has a switch unit SWa having one end connected to the gate input terminal side of the switching element Q and the other end connected to the reference potential side, and between the switch unit SWa and the gate input terminal. Since the capacitor Ca and the Zener diode ZD connected in series are suitable for relatively simple high-speed switching, the current value Ia (voltage value Va) is set to the second threshold value (second reference voltage value Vref2). ) Can be lowered to the breakdown voltage Vzd of the Zener diode ZD in a very short time (response time is short).

  Moreover, when the current value Ia (voltage value Va) temporarily exceeds the second threshold value (second reference voltage value Vref2), that is, no load short-circuit has occurred, for example, a normal turn-on operation (Vg2 = Vcc ), The gate voltage Vg2 is temporarily reduced by the gate voltage adjusting unit 42 as shown at time points t5 to t6 in FIG. However, the current value Ia does not exceed the first threshold value (reference voltage value Vref1), and corresponds to the fact that the current value Ia has fallen below the second threshold value (second reference voltage value Vref2) smaller than the first threshold value (reference voltage value Vref1). Since the normal gate voltage Vg2 is immediately applied to the gate input terminal, the normal switching operation can be continued without erroneously detecting a load short circuit. In this case, the protection circuit 41 does not operate.

  Further, when the current value Ia exceeds the first threshold value (reference voltage value Vref1) set to a value larger than the second threshold value (reference voltage Vref2), the protection circuit 41 operates by assuming that a load short circuit has occurred. Therefore, the application of the gate voltages Vg1 and Vg2 to the gate input terminal is cut off. As a result, the drain current Id flowing through the switching element Q is also cut off, the operation of the switching element Q is stopped, and the switching element Q is protected.

  As described above, the first threshold value (reference voltage Vref1) set in the protection circuit 41 is larger than the second threshold value (reference voltage value Vref2) set in the gate voltage adjustment unit 42 in order to prevent erroneous detection of the load short circuit. Since it is configured to include an appropriate delay filter or the like (corresponding to the delay time Td of the gate control circuit 54), the response time is longer than that of the gate voltage adjustment unit 42. That is, the delay time Td occurs from when the current value Ia exceeds the first threshold value (first reference voltage value Vref1) to when the gate drive voltage Vg1 starts to be cut off.

  Therefore, when the application of the gate voltages Vg1 and Vg2 is to be interrupted only by the protection circuit 41 when the load is short-circuited, the time until the gate voltages Vg1 and Vg2 are interrupted is the normal gate drive voltage. A gate end voltage Vg2 due to Vg1 is applied, and a relatively large drain current Id flows to the switching element Q. According to this embodiment, when the load is short-circuited (time point t9), When the gate voltage adjustment unit 42 that operates at a high speed with a short response time first reduces the gate terminal voltage Vg2, and when the current value Ia becomes so large that the load short circuit is determined {the current value Ia is the first threshold value ( When the first reference voltage value Vref1) is exceeded}, the gate drive voltage Vg1 can be cut off by the protection circuit 41, so that the switching element Q when the load is short-circuited While reducing the current flowing until the stop (energy), it is possible to suppress the erroneously detects the load short-circuit.

  Furthermore, the gate voltage adjustment unit 42 includes a capacitor Ca and a Zener diode ZD connected between the switch unit SWa and the gate input terminal, so that the current value Ia is a second threshold value (second reference voltage value). When Vref2) is exceeded, the gate terminal voltage Vg2 input to the gate input terminal of the switching element Q is first lowered to the breakdown voltage Vzd of the Zener diode ZD, and then the Zener diode ZD is charged with the charging of the capacitor Ca. Since the flowing Zener current Izd becomes smaller, the heat generation of the Zener diode ZD can be reduced. Therefore, compared with the case where the zener diode ZD is configured only (see FIG. 8 according to Patent Document 1), the heat generated by the zener diode ZD can be reduced and the zener diode ZD can be downsized.

  With reference to FIG. 6 which is a schematic diagram, the heat generation reduction of the Zener diode ZD will be described visually. When the Zener diode ZD is in a breakdown state at the time t11 during the increase of the drain current Id, this embodiment and FIG. In the eight examples, the gate input terminal decreases from the driving voltage Vcc to Vcc-Vzd (Vcc-Vzp: FIG. 8). Until time t11, the zener current Izd (Izp: FIG. 8) is 0 [A], and at time t11, the power increases from 0 [W] to zener power Wzdmax (Wzpmax: FIG. 8) [W]. To do. In this embodiment, since the capacitor Ca is charged after the time t11, the Zener current Izd decreases accordingly. In the example of FIG. 8, since the capacitor Ca is not present, the Zener current Izp is equal to the state at the time t11. does not change. For this reason, the Zener power Wzd in this embodiment is shown in the curve 100 from the time point t11 to the virtual time point ti at which the power Wzd of the Zener diode ZD is less than the breakdown voltage Vzd of the Zener diode ZD and is 0 [W]. In the example of FIG. 8, the zener power Wzp of the zener diode 120 is until the virtual time point ti of the power 0 [W] at which the zener diode 120 becomes less than the breakdown voltage Vzp, as indicated by a one-dot chain line. No change from time t11.

  According to this embodiment, the gate terminal voltage Vg2 input to the gate input terminal is gradually increased as the capacitor Ca is charged. Since the application of the voltage Vg1 (Vg2) is interrupted, the drain current Id flowing through the switching element Q can be interrupted before the drain current Id flowing through the switching element Q increases.

  As described above, in this embodiment, the protection circuit 41 has a gate terminal voltage that causes the gate terminal voltage Vcc-Vzd, which has been lowered by the Zener diode ZD of the gate voltage adjustment unit 42, to be normally turned on by charging the capacitor Ca. It is provided to cut off the application of the gate end voltage Vg2 before it rises to Vg2 = Vcc.

  Further, the protection circuit 41 and the gate voltage adjustment unit 42 according to this embodiment use the first and second comparisons to set the first threshold value and the second threshold value to the first reference voltage value Vref1 and the second reference voltage value Vref2, respectively. Detectors 51 and 52, and in order to compare the current value Ia (voltage value Va) and the threshold values (first and second reference voltage values Vref1 and Vref2), the detected current proportional to the drain current Id flowing through the switching element Q Ia is caused to flow through the resistor Ra, and the voltage across the resistor Ra is set as the comparison voltage value Va. When the comparison voltage value Va exceeds the second reference voltage value Vref2, the second voltage constituting the gate voltage adjustment unit 42 is formed. When the switch section Spa is turned on by the switch signal Sp2 which is the transition output of the comparator 52, and then the comparison voltage value Va exceeds the first reference voltage value Vref1. Since the application of the gate voltage (gate drive voltage Vg1) is cut off by the protection signal Sp1 which is the transition output of the first comparator 51 constituting the protection circuit 41, noise caused by the gate voltage adjustment unit 42 is short-circuited to the load. Preliminary high-speed protection that protects the switching element Q while avoiding false detection and irreversible protection of the switching element Q when the load is short-circuited by the protection circuit 41, respectively, an accurate current value Ia of a constant value. Can be started by using the first and second comparators 51 and 52 in which the first and second reference voltage values Vref1 and Vref2 corresponding to are set, respectively. With the value Va), accurate and uniform malfunction control and protection control can be performed.

  That is, according to this embodiment, since the capacitor Ca is connected in series to the protective Zener diode ZD, the threshold value (the first threshold) at which the protective circuit 41 operates while suppressing the heat generation of the protective Zener diode ZD during protection. 1 threshold value) The voltage corresponding to the current value Ia can be suppressed by the gate voltage adjusting unit 42 having a threshold value (second threshold value) Vref2 set to a relatively small value compared to Vref1. Since the value Va is compared by the first and second comparators 51 and 52, accurate and uniform malfunction control and protection control are performed with a constant detection (comparison) current value {detection (comparison) voltage value}. Can do.

  Note that the present invention is not limited to the above-described embodiment, and various configurations are adopted based on the description in this specification, such as a modification to the short-circuit current protection device 10a according to another embodiment shown in FIG. Of course you get.

  In the short-circuit current protection device 10a having the gate voltage adjustment unit 42a in the example of FIG. 7, the second comparator 52 in FIG. 2 is omitted and the switch unit SWa is directly driven by the voltage value Va. If a MOSFET that is measured and selected in advance for the gate threshold voltage Vgsth of the MOSFET used for SWa is used, it can be operated with the same accuracy as in the example of FIG. Even if it is not selected, it is possible to obtain a protective effect with a certain accuracy.

DESCRIPTION OF SYMBOLS 10, 10a ... Short-circuit current protective device 12 ... Electric vehicle 16 ... Inverter 18 ... Drive motor 41 ... Protection circuit 42, 42a ... Gate voltage adjustment part 51 ... 1st comparator 52 ... 2nd comparator 54 ... Gate control circuit Ca ... Capacitor Q (Q1 to Q6) ... Switching element ZD ... Zener diode

Claims (4)

In a short-circuit current protection device for a power converter equipped with a switching element,
A gate control circuit for controlling turn-on and turn-off of the switching element by applying a predetermined drive voltage as a gate voltage to the gate input terminal of the switching element;
A current detection unit for detecting a current value flowing through the switching element;
A protection circuit that detects that the current value has exceeded a first threshold, and that blocks application of the gate voltage by the gate control circuit after a first time after detection;
It is detected that the current value has exceeded a second threshold value smaller than the first threshold value, and the gate voltage is reduced below the drive voltage after a second time shorter than the first time after the detection. And when the current value exceeds the second threshold value and then falls below the second threshold value, a gate voltage adjustment unit that applies the drive voltage;
A short-circuit current protection device comprising: In the short circuit current protection device according to claim 1,
The gate voltage adjustment unit is
One end is connected to the gate input terminal side, the other end is connected to the reference potential side, and the switch unit becomes conductive when the current value exceeds the second threshold value which is smaller than the first threshold value;
A capacitor and a Zener diode connected in series between the switch unit and the gate input terminal;
A short-circuit current protection device comprising: In the short circuit current protection device according to claim 2,
In the protection circuit, the gate voltage lowered by the Zener diode of the gate voltage adjusting unit at the time of a short circuit rises due to charging of the capacitor, and the current value flowing through the switching element is a deterioration start limit current value or The short-circuit current protection device characterized in that the gate voltage is cut off before a certain level of deterioration increases to an allowable current value. In the short circuit current protection device according to any one of claims 2 and 3,
The protection circuit and the gate voltage adjustment unit are:
A first comparator and a second comparator, each of which uses the first threshold and the second threshold as a first reference voltage value and a second reference voltage value,
In order to compare the current value with the threshold value, a current flowing through the switching element is passed through a resistor to set a voltage at both ends of the resistor as a comparison voltage value, and the comparison voltage value exceeds the second reference voltage value. The gate voltage adjustment unit causes the switch unit to be in a conductive state, and then the protection circuit cuts off the application of the gate voltage when the comparison voltage value exceeds the first reference voltage value. A short-circuit current protection device.

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