JP2016086588A - Drive device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a drive device which reduces a filter time for short-circuit judgment while preventing incorrect protection operation due to a noise.SOLUTION: The drive device includes: a sense current detection unit 100 which detects the output current of a power switching element 20; a voltage change detection unit 200 which detects an output voltage change of the power switching element; and a short-circuit detection unit 300 which judges a short-circuit in the power switching element, according to input signals from the sense current detection unit and the voltage change detection unit. The short-circuit detection unit judges the existence or non-existence of a short-circuit on the basis of a pre-defined change in the output voltage in a state that the output current exceeds a predetermined threshold.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a drive device that controls driving of a power switching element, and particularly has a protection capability against an overcurrent generated in the power switching element.

  As an example of a conventional drive device with a protective function, a switching circuit described in Patent Document 1 can be cited. In this switching circuit, an increase in collector voltage due to a load short-circuit in an IGBT as a power switching element is detected by an external Zener diode.

JP 2006-295326 A

  Generally, in detecting a short circuit, the protection operation is performed under the condition that the state where the output current flowing through the power switching element exceeds the threshold is maintained for a certain filter time. This is to prevent malfunction when the output current exceeds a threshold value due to noise. However, if the filter time is too long, the stress received by the power switching element due to a large current due to a short circuit increases, and power is wasted during the filter time. Therefore, it is desirable to set the filter time as short as possible. That is, the filter time has a trade-off relationship between the power consumption of the power switching element and the noise care. In general, it is set to 1 μs to 2 μs.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a control device capable of reducing the filter time while preventing an erroneous protection operation due to noise.

  The invention disclosed herein employs the following technical means to achieve the above object. Note that the reference numerals in parentheses described in the claims and in this section indicate a corresponding relationship with specific means described in the embodiments described later as one aspect, and limit the technical scope of the invention. Not what you want.

  In order to achieve the above object, the present invention provides a drive device for controlling on / off of a power switching element (20, 50, 60, 70), and a sense current detection unit (100) for detecting an output current of the power switching element. ), A voltage change detection unit (200) that detects a change in the output voltage of the power switching element, and a short circuit detection unit that determines a short circuit of the power switching element in accordance with input signals from the sense current detection unit and the voltage change detection unit (300), and the short circuit detector further determines whether or not there is a short circuit based on a predetermined change in the output voltage in a state where the output current exceeds a predetermined threshold value. It is said.

  According to this, in addition to the conventional short-circuit determination condition that the output current of the power switching element exceeds a predetermined threshold, a short circuit is detected by detecting a predetermined change in the output voltage. It has become. Therefore, the frequency of malfunction due to noise can be suppressed as compared with the conventional short circuit determination. In addition, since the output voltage at the time of a short circuit can be changed in ns (nanosecond) order, the time until the short circuit determination can be shortened compared with the filter time (1 microsecond-2 microseconds) set conventionally. . Therefore, power consumption in the power switching element can be reduced, and stress on the power switching element can be reduced.

  Regarding the change in the output voltage, for example, the voltage change detection unit detects the time change of the output voltage by configuring a differentiation circuit with the capacitor and the resistor (220), and the short circuit detection unit detects that the output current is a predetermined threshold value. If the intermediate potential between the capacitor and the resistor becomes positive in a state in which the power switching element is exceeded, the power switching element can be determined to be in a short-circuit state.

  For example, in the situation where a short circuit does not occur at turn-on, the output voltage decreases with time, but in a situation where a short circuit occurs, it rises again due to saturation of the output current after a temporary voltage decrease. Turn to. The voltage change detection unit in the above configuration can detect a short circuit with respect to the increase in the output voltage because the time derivative of the voltage is positive.

  As another example of the change in the output voltage, the voltage change detection unit includes a diode (240, 270), a pull-up power source (250), and a pull-up resistor (260). , The anode terminal is connected to the terminal upstream of the output current, and the pull-up power supply has a voltage between the terminal voltage VH upstream of the output current, the voltage VB of the pull-up power supply, and the forward voltage Vf of the diode. Is connected to the cathode terminal of the diode via a pull-up resistor so that VB−Vf ≦ VH is satisfied, and the short-circuit detection unit is connected to the potential of the cathode terminal of the diode in a state where the output current exceeds a predetermined threshold. Can be configured to determine that the power switching element is in a short-circuit state by maintaining the pull-up voltage longer than a predetermined determination time. .

  In such a configuration, in a situation where a short circuit does not occur at the time of turn-on, the output voltage transitions from a state higher than Vf to a state lower than Vf as time elapses, so that the potential of the cathode terminal in the diode becomes the pull-up voltage VB. To the forward voltage Vf of the diode. On the other hand, in a situation where a short circuit has occurred, after the output voltage temporarily drops, the output current starts to rise again due to saturation of the output current, so that the output voltage remains higher than Vf regardless of the passage of time. become. Therefore, in a situation where a short circuit has occurred, the potential of the cathode terminal of the diode maintains the pull-up voltage VB. The voltage change detection unit in the above configuration can detect a short circuit in the power switching element because the potential of the cathode terminal of the diode maintains the pull-up voltage longer than a predetermined determination time.

It is a figure which shows schematic structure of the drive device and peripheral circuit which concern on 1st Embodiment. It is a circuit diagram which shows the detail of a drive device and a power switching element. It is a figure which shows the electric current and voltage of each terminal at the time of normal drive. It is a figure which shows the electric current and voltage of each terminal at the time of short circuit occurrence. FIG. 10 is a circuit diagram illustrating details of a drive device and a power switching element according to Modification 1; It is a circuit diagram which shows the detail of the drive device and power switching element which concern on 2nd Embodiment. It is a figure which shows the electric current and voltage of each terminal at the time of normal drive. It is a figure which shows the electric current and voltage of each terminal at the time of short circuit occurrence. It is a figure which shows a connection structure to a power switching element and load. It is a circuit diagram which shows the detail of the drive device which concerns on the modification 2, and a power switching element. It is a circuit diagram which shows the detail of the drive device which concerns on the modification 3, and a power switching element.

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

(First embodiment)
Initially, with reference to FIG. 1 and FIG. 2, schematic structure of the drive device which concerns on this embodiment is demonstrated.

  As shown in FIG. 1, the driving device 10 is a circuit for controlling driving of the power switching element. The power switching element turns on and off the supply of current to a load (not shown), and an insulated gate bipolar transistor (IGBT), a MOS transistor, or the like can be adopted. In the present embodiment, for example, a circuit for driving the IGBT 20 as a power switching element will be described.

  As shown in FIG. 1, the drive device 10 includes a sense current detection unit 100, a voltage change detection unit 200, a short circuit detection unit 300, and a control unit 400 that controls application of a gate voltage to the IGBT 20. ing.

  The IGBT 20 is controlled to be turned on and off by applying a predetermined gate voltage (VCC shown in FIG. 1) to the gate terminal. The gate terminal of the IGBT 20 is connected to an intermediate point between the on-side circuit 30 and the off-side circuit 40 connected in series between a voltage VCC supplied from a power supply (not shown) and the ground GND. When the IGBT 20 is turned on, VCC is applied to the gate terminal of the IGBT 20 by turning on the on-side circuit 30 and turning off the off-side circuit 40. On the other hand, when the IGBT 20 is turned on, the on-side circuit 30 is turned off and the off-side circuit 40 is turned on, whereby charges are extracted from the gate terminal of the IGBT 20. As shown in FIG. 2, the IGBT 20 in the present embodiment includes a main cell 21, a sense cell 110, and a subcell 210, which will be described later, formed on a single substrate. The IGBT 20 includes a sense current detection unit 100 and a voltage change detection unit. 200 is included.

  The output current of the IGBT 20 is a collector-emitter current (hereinafter referred to as a collector current) of the main cell 21 and flows when a voltage VCC is applied to the gate terminal. The collector current flows through the emitter terminal (Kelvin emitter terminal: KE terminal) of the main cell 21.

  As shown in FIG. 2, the sense current detection unit 100 includes a sense cell 110 formed in the IGBT 20, and a sense resistor formed between the emitter terminal (first sense emitter terminal: SE1 terminal) of the sense cell 110 and the ground. 120. The sense cell 110 is formed on the same semiconductor substrate as the main cell 21, and the gate terminal of the sense cell 110 is commonly connected to the gate terminal of the main cell 21. The collector terminal of the sense cell 110 is commonly connected to the collector terminal of the main cell 21. When a voltage is applied to the gate terminal of the main cell 21, a voltage is also applied to the gate terminal of the sense cell 110, and a current (hereinafter referred to as a sense current) that is approximately proportional to the collector current that is the output current of the IGBT 20 is applied to the SE 1 terminal. Current). The SE1 terminal is connected to the short-circuit detection unit 300, and the voltage defined by the sense current and the sense resistor 120 is input to the short-circuit detection unit 300. That is, the sense current detection unit 100 can indirectly detect the collector current of the IGBT 20.

  As shown in FIG. 2, the voltage change detection unit 200 includes a subcell 210 formed in the IGBT 20, and a subresistor formed between the emitter terminal (second sense emitter terminal: SE2 terminal) of the subcell 210 and the ground. 220. Like the sense cell 110, the subcell 210 is formed on the same semiconductor substrate as the main cell 21, and the collector terminal of the subcell 210 is commonly connected to the collector terminal of the main cell 21. The subcell 210 has its gate terminal and emitter terminal connected to each other, and the internal capacitance of the subcell 210 constitutes a feedback capacitance. The collector terminal of the subcell 210 is at the same potential as the output voltage of the main cell 21 (hereinafter referred to as the collector voltage). In the voltage change detection unit 200 in the present embodiment, a voltage (dV / dt) corresponding to the time change of the collector voltage is output to the SE1 terminal. That is, a differential circuit is formed by the feedback capacitance of the subcell 210 and the subresistor 220. The SE1 terminal is connected to the short-circuit detection unit 300, and the time derivative dV / dt of the collector voltage is input to the short-circuit detection unit 300.

  The short circuit detection unit 300 is connected to the sense current detection unit 100 and the voltage change detection unit 200 as inputs, and outputs a signal based on these inputs to the control unit 400. The short circuit detection unit 300 compares the voltage corresponding to the sense current input from the sense current detection unit 100 with a predetermined threshold. Since the sense current is substantially proportional to the collector current of the main cell 21, the short-circuit detection unit 300 can detect that the collector current is in an overcurrent state when the sense current is equal to or greater than a predetermined threshold. . For example, when the sense current is greater than or equal to a predetermined threshold, the short-circuit detection unit 300 holds the digital value “1” in a memory or the like built therein.

  In addition, the short-circuit detection unit 300 incorporates a digital value “1” in itself when dV / dt takes a positive value for the time derivative dV / dt of the collector voltage input from the voltage change detection unit 200. Hold it in memory etc. The predetermined change in the output voltage described in the claims corresponds to a positive transition of dV / dt in the present embodiment.

  In the conventional configuration, it is determined that a load short circuit (not shown) has occurred because the state where the sense current is equal to or greater than the predetermined threshold is continued for the filter time. In contrast, the short circuit detection unit 300 according to the present embodiment has a short circuit when the logical product of the input from the sense current detection unit 100 and the input from the voltage change detection unit 200 is “1”. Judge. That is, it is determined that a short circuit has occurred under the condition that the sense current is equal to or greater than a predetermined threshold and dV / dt is positive. On the other hand, when the logical product is “0”, it is determined that there is no short circuit. The short-circuit detection unit 300 instructs the control unit 400 to perform a predetermined operation based on the logical product value. For example, if the logical product is “1”, the control unit 400 is instructed to stop or limit the operation of the IGBT 20. If the logical product is “0”, the control unit 400 is informed of the IGBT 20. Instruct to continue operation.

  However, when the determination of the short circuit in the short circuit detection unit 300 described above is used together with the determination of the short circuit in the conventional configuration, the power switching element can be driven more safely. For example, if the sense current continues beyond the conventional filter time even if the sense current is not less than a predetermined threshold and dV / dt does not transition positively, a short circuit occurs. By configuring so as to determine that there is a short circuit, a double check for a short circuit can be performed.

  The control unit 400 controls on / off of the on-side circuit 30 and the off-side circuit 40 to control injection or extraction of charges to the gate terminals of the main cell 21 and the sense cell 110 constituting the IGBT 20. The control unit 400 is communicably connected to the short circuit detection unit 300 and controls the operation of the IGBT 20 based on a signal input from the short circuit detection unit 300.

  Next, with reference to FIG. 3 and FIG. 4, the operation | movement and effect of the drive device 10 in this embodiment are demonstrated.

  3 and 4 show the turn-on operation of the IGBT 20. First, a normal operation in which no short circuit occurs will be described with reference to FIG. Prior to time t1, the on-side circuit 30 is turned off and the off-side circuit 40 is turned on, and a constant collector voltage is applied to the collector terminal of the main cell 21. Since the IGBT 20 is in an off state, no collector current flows. Since the voltage at the SE1 terminal corresponds to the collector current of the main cell 21, the ground potential is maintained. The voltage at the SE2 terminal is the time change dV / dt of the collector voltage V. Since the collector voltage does not change before time t1, the ground potential is maintained.

  At time t1, the control unit 400 turns on the on-side circuit 30 and turns off the off-side circuit 40. As a result, a voltage is applied to the gate terminals of the main cell 21 and the sense cell 110 and the collector current begins to flow. The collector voltage decreases as the collector current increases. Since the collector voltage changes, an induced electromotive force is generated due to the parasitic inductance of the circuit, and the collector voltage becomes constant at time t2. The voltage at the SE1 terminal increases corresponding to the increase in collector current. The voltage at the SE2 terminal transitions to the negative side in response to a decrease in the collector voltage.

  When the time t2 is reached, the collector voltage becomes constant as described above. The collector current continues to increase from time t1, and accordingly, the voltage at the SE1 terminal also increases. The voltage at the SE2 terminal is almost the ground potential because the collector voltage changes from a decrease to a constant value.

  When reaching the time t3, the collector voltage starts decreasing again. The voltage at the SE2 terminal transitions to the negative side in response to a decrease in the collector voltage.

  When the collector current reaches a constant value corresponding to the gate voltage at time t4, the collector voltage becomes the ground potential. The voltage at the SE1 terminal also becomes a constant value corresponding to the collector current. Corresponding to the collector voltage being constant at the ground potential, the voltage at the SE2 terminal is also substantially constant at the ground potential.

  In the operation example shown in FIG. 3, the voltage at the SE1 terminal does not exceed the determined threshold value. In other words, the collector current does not exceed the predetermined threshold. Therefore, the sense current detection unit 100 outputs the digital value “0” to the short circuit detection unit 300. In addition, the SE2 terminal voltage has two transitions to the negative side, but does not transition to the positive side. Therefore, the voltage change detection unit 200 outputs the digital value “0” to the short circuit detection unit 300. Therefore, the short circuit detection unit 300 recognizes the logical product “0” of the digital values output from the sense current detection unit 100 and the voltage change detection unit 200 and continues the turn-on operation of the IGBT 20 to the control unit 400. To instruct.

  Next, an operation when a short circuit occurs will be described with reference to FIG. Prior to time t5, the on-side circuit 30 is turned off and the off-side circuit 40 is turned on, which is the same as before time t1 during normal driving (FIG. 3), and thus detailed description thereof is omitted. Further, the process from time t5 to time t6 is the same as time t1 to time t2 during normal driving, and therefore detailed description is omitted.

  After time t6, the collector voltage maintains a constant value. The collector current continues to increase from time t5.

  At time t7, the voltage at the SE1 terminal reaches a predetermined threshold value. In other words, the collector current reaches a predetermined threshold value. Thereby, the short circuit detection unit 300 holds the digital value “1” in a memory or the like. In the operation example shown in FIG. 4, the collector current also increases after time t7.

  When the collector current reaches the saturation current of the IGBT 20 at time t8, the collector voltage starts to increase. For this reason, the voltage at the SE2 terminal shifts to the positive side. The short circuit detection unit 300 holds the digital value “1” in a memory or the like at time t8.

  In the operation example shown in FIG. 4, the collector current exceeds a predetermined threshold at time t7, and the situation is maintained until time t8. At time t8, the voltage at the SE2 terminal changes to the positive side. The short-circuit detection unit 300 recognizes the logical product “1” based on the outputs from the sense current detection unit 100 and the voltage change detection unit 200, and a short-circuit occurs in the load, resulting in an overload caused by the short-circuit in the IGBT 20. It is determined that a large current is flowing. The short circuit detection unit 300 instructs the control unit 400 to stop or limit the turn-on operation of the IGBT 20.

  In the conventional configuration, a short circuit is detected by maintaining that the collector current exceeds the threshold value for a predetermined filter time from time t7. In general, the filter time is generally 1 μs to 2 μs from the viewpoint of noise care. On the other hand, in this embodiment, a short circuit can be detected at time t8 after detecting an excess of the collector current with respect to the threshold value at time t7. Although the time from time t7 to time t8 depends on the connected load, it is on the order of 1 ns to 100 ns, and a short circuit can be detected in a shorter time than the conventional filter time. Further, the short circuit detection unit 300 determines a short circuit of the load when both of the sense current detection unit 100 and the voltage change detection unit 200 detect a short circuit. That is, a double check is performed for a short circuit. Therefore, by adopting the drive device 10 according to the present embodiment, it is possible to reduce the filter time while preventing erroneous protection operation due to noise.

(Modification 1)
In the above-described embodiment, the example in which the IGBT 20 is used as the power switching element has been described. However, the present invention is not limited to this. For example, as illustrated in FIG. 5, a MOS transistor 50 may be employed as the power switching element. .

  Similar to the IGBT 20, the MOS transistor 50 includes a main cell 51, a sense cell 130, and a subcell 230. The drive device 11 in this modification has a structure in which the main cell 21, the sense cell 110, and the subcell 210 of the IGBT 20 are replaced with the main cell 51, the sense cell 130, and the subcell 230 of the MOS transistor 50, respectively, in the first embodiment. doing. The drain terminals of the main cell 51, the sense cell 130, and the subcell 230 are connected in common. The main cell 51 and the sense cell 130 have a common gate terminal. In the subcell 230, the gate terminal and the source terminal are connected to each other, and the internal capacitance forms a feedback capacitance. The source terminals of the main cell 51, the sense cell 130, and the subcell 230 correspond to the KE terminal, SE1 terminal, and SE2 terminal in the first embodiment, respectively.

  Since the driving device 11 in this modification is obtained by replacing each cell 21, 110, 210 of the IGBT 20 with a MOS transistor as compared with the first embodiment, the sense cell 130 and the sense resistor 120 include the sense current detection unit 100. The subcell 230 and the subresistor 220 constitute the voltage change detection unit 200. The configurations of the short circuit detection unit 300 and the control unit 400 are the same as those in the first embodiment.

  Note that the operation and effect of the driving device 11 are the same as those of the driving device 10 in the first embodiment. Regarding the description of the first embodiment, the collector current is the drain current, the collector terminal is the drain terminal, and the emitter terminal is the source. In other words, the expression of each terminal can explain the operational effects of the present modification. Therefore, by adopting the driving device 11 according to this modification, it is possible to reduce the filter time while preventing erroneous protection operation due to noise.

(Second Embodiment)
The driving device 12 in the present embodiment drives the IGBT 60 as a power switching element. The difference from the driving apparatus 10 described in the first embodiment is the configuration and operation of the voltage change detection unit 200 due to the difference in structure between the IGBT 20 and the IGBT 60.

  First, with reference to FIG. 6, the structure of the driving device 12 according to the present embodiment that is different from the first embodiment will be described.

  As shown in FIG. 6, the IGBT 60 includes a main cell 61, a sense cell 140, and a diode 240 formed on the same semiconductor substrate. The main cell 61 and the sense cell 140 of the IGBT 60 have the same configuration as the main cell 21 and the sense cell 110 of the IGBT 20 in the first embodiment, respectively, and the emitter terminal of the main cell 61 corresponds to the KE terminal, and the emitter terminal of the sense cell 140 Corresponds to the SE1 terminal. The cathode terminal of the diode 240 corresponds to the SE2 terminal. The collector terminals of the main cell 61 and the sense cell 140 and the anode terminal of the diode 240 are connected in common. The main cell 61 and the sense cell 140 are connected in common at the gate terminal.

  The sense current detection unit 100 in the present embodiment is the same as the configuration of the sense current detection unit 100 in the first embodiment. Specifically, the sense current detection unit 100 includes a sense cell 140 and a sense resistor 120, and detects the current by converting the sense current into a voltage. The SE1 terminal is connected to the short-circuit detection unit 300, and the voltage defined by the sense current and the sense resistor 120 is input to the short-circuit detection unit 300. That is, the sense current detection unit 100 can indirectly detect the collector current of the IGBT 60.

  The voltage change detection unit 200 according to the present embodiment includes a diode 240 built in the IGBT 60, a pull-up power supply 250, and a pull-up resistor 260. The anode terminal of the diode 240 is connected to the collector terminal of the main cell 61, and the cathode terminal (SE 2 terminal) is connected to the pull-up power supply 250 via the pull-up resistor 260. As in the first embodiment, the SE2 terminal is connected to the short-circuit detection unit 300.

  Here, a high-voltage power source for driving a load is applied to the collector terminal of the main cell 61. That is, the voltage (hereinafter referred to as VH) applied to the anode side of the main cell 61, the sense cell 140, and the diode 240 corresponds to the upstream terminal voltage described in the claims. The voltage VH satisfies the relationship of VB−Vf ≦ VH between the voltage VB designated as the pull-up power supply and the forward voltage Vf of the diode 240.

  In the voltage change detection unit 200 configured as described above, when the collector voltage is equal to or higher than Vf, no current flows through the diode 240, and the voltage at the SE2 terminal is VB. On the other hand, when the collector voltage falls below Vf, a current flows through the diode 240, and the voltage at the SE2 terminal is clamped at Vf. As described in the first embodiment, in a normal drive in which a short circuit does not occur, the collector voltage decreases due to the turn-on operation of the IGBT 60 and falls below Vf, so that the voltage at the SE2 terminal at that time transitions from VB to Vf. . On the other hand, in the drive in which a short circuit occurs, the collector voltage does not decrease sufficiently, and the voltage at the SE2 terminal maintains VB.

  The short circuit detection unit 300 is connected to the sense current detection unit 100 and the voltage change detection unit 200 as inputs, and outputs a signal based on these inputs to the control unit 400. The short circuit detection unit 300 compares the voltage corresponding to the sense current input from the sense current detection unit 100 with a predetermined threshold. Since the sense current is substantially proportional to the collector current of the main cell 61, the short-circuit detection unit 300 can detect that the collector current is in an overcurrent state when the sense current is equal to or greater than a predetermined threshold. . For example, when the sense current is greater than or equal to a predetermined threshold, the short-circuit detection unit 300 holds the digital value “1” in a memory or the like built therein.

  In addition, the short-circuit detection unit 300 is digital when the voltage of the SE2 terminal input from the voltage change detection unit 200 is maintained at VB for a predetermined determination time from the time when the sense current exceeds the threshold value. The value “1” is held in a memory or the like built in itself. In the present embodiment, the predetermined change in the output voltage described in the claims corresponds to that the voltage at the SE2 terminal is maintained at VB for a predetermined determination time and does not change. . The determination time will be described in detail later.

  Next, with reference to FIG. 7 and FIG. 8, operation | movement and an effect of the drive device 12 which concern on this embodiment are demonstrated.

  7 and 8 show the turn-on operation of the IGBT 20. First, a normal operation in which no short circuit occurs will be described with reference to FIG. Prior to time t1, the on-side circuit 30 is turned off and the off-side circuit 40 is turned on, and a constant collector voltage is applied to the collector terminal of the main cell 61. Since the IGBT 60 is in an off state, no collector current flows. Since the voltage at the SE1 terminal corresponds to the collector current of the main cell 61, the ground potential is maintained. Since the collector voltage is kept higher than Vf, the voltage at the SE2 terminal is VB.

  At time t1, the control unit 400 turns on the on-side circuit 30 and turns off the off-side circuit 40. As a result, a voltage is applied to the gate terminals of the main cell 61 and the sense cell 140, and the collector current begins to flow. The collector voltage decreases as the collector current increases. Since the collector voltage changes, an induced electromotive force is generated due to the parasitic inductance of the circuit, and the collector voltage becomes constant at time t2. The voltage at the SE1 terminal increases corresponding to the increase in collector current. Although the collector voltage decreases but does not fall below Vf, the voltage at the SE2 terminal maintains VB.

  When time t2 is reached, the collector voltage becomes constant at a value defined by the induced electromotive force due to VH and the parasitic inductance of the circuit. The collector current continues to increase from time t1, and accordingly, the voltage at the SE1 terminal also increases. The voltage at the SE2 terminal is continuously maintained at VB.

  When reaching the time t3, the collector voltage starts decreasing again. At time t4, when the collector voltage falls below Vf, a current flows through the diode 240, and the SE2 terminal changes to Vf. The collector current is constant at a value corresponding to the gate voltage, and the voltage at the SE1 terminal is also constant at a value corresponding to the collector current.

  In the operation example shown in FIG. 7, the voltage at the SE1 terminal does not exceed the determined threshold value. In other words, the collector current does not exceed the predetermined threshold. Therefore, the sense current detection unit 100 outputs the digital value “0” to the short circuit detection unit 300. Further, the voltage at the SE2 terminal changes from VB to Vf at time t4 and does not maintain VB. Therefore, the voltage change detection unit 200 outputs the digital value “0” to the short circuit detection unit 300. Therefore, the short circuit detection unit 300 recognizes the logical product “0” of the digital values output from the sense current detection unit 100 and the voltage change detection unit 200 and continues the turn-on operation of the IGBT 20 to the control unit 400. To instruct.

  Next, the operation when a short circuit occurs will be described with reference to FIG. Prior to time t5, the on-side circuit 30 is turned off and the off-side circuit 40 is turned on, which is the same as before time t1 during normal driving (FIG. 7), and thus detailed description is omitted. Further, the process from time t5 to time t6 is the same as time t1 to time t2 during normal driving, and therefore detailed description is omitted.

  After time t6, the collector voltage maintains a constant value. The collector current continues to increase from time t5.

  At time t7, the voltage at the SE1 terminal reaches a predetermined threshold value. In other words, the collector current reaches a predetermined threshold value. Thereby, the short circuit detection unit 300 holds the digital value “1” in a memory or the like. In the operation example shown in FIG. 8, the collector current also increases after time t7. At this time, the collector voltage is equal to or higher than Vf, and the voltage at the SE2 terminal is maintained at VB. The short circuit detector 300 starts counting a predetermined determination time from time t7.

  Since the collector voltage does not fall below Vf at time t8 when the determination time has elapsed from time t7, the voltage at the SE2 terminal maintains VB. The short-circuit detection unit 300 outputs the digital value “1” to the memory or the like at time t8.

  In the operation example shown in FIG. 8, the collector current exceeds a predetermined threshold at time t7, and the situation is maintained until time t8. During the determination time from time t7 to time t8, the voltage at the SE2 terminal is maintained at VB. The short-circuit detection unit 300 recognizes the logical product “1” based on the outputs from the sense current detection unit 100 and the voltage change detection unit 200, and a short-circuit occurs in the load, resulting in an overload caused by the short-circuit in the IGBT 20. It is determined that a large current is flowing. The short circuit detection unit 300 instructs the control unit 400 to stop or limit the turn-on operation of the IGBT 20.

  In the conventional configuration, a short circuit is detected by maintaining that the collector current exceeds the threshold value for a predetermined filter time from time t7. Even in the configuration of the present embodiment, it is the same that a short circuit is detected with a predetermined determination time from time t7, but this determination time is not a collector current but a time during which the collector voltage is maintained at Vf or higher. It is something to monitor. When a short circuit occurs, as shown in FIG. 8, the collector current is saturated and the collector voltage does not decrease and starts to increase, so it does not fall below Vf. In other words, the determination time may be ensured from when the collector current becomes equal to or higher than the predetermined threshold until it is saturated.

  For example, as shown in FIG. 9, the time until the collector current is saturated, that is, the determination time, is the drive voltage V for driving the load by the internal resistance R of the IGBT 60 and the parasitic inductance L generated in the circuit, and the ground. It can be roughly estimated by the time constant τ (= L / R) in the LR circuit connected in series with the potential. Specifically, as the determination time, a time equal to or greater than the time constant τ may be secured. Since the collector current almost saturates after elapse of the time constant τ times the number of Napiers, that is, eτ (e is the number of Napiers) after starting to rise, it is sufficient to set the determination time to eτ. For example, the parasitic inductance L in this embodiment is on the order of 100 nH. Assuming that the internal resistance of the IGBT 60 is about 1Ω, τ≈100 ns, and the determination time can be set to approximately 300 ns.

  The filter time in the conventional configuration is 1 μs to 2 μs as described above. Although the determination time in this embodiment depends on the inductance L of the connected load, it is on the order of 10 ns to 100 ns, and a short circuit can be detected in a shorter time than the conventional filter time. Further, the short circuit detection unit 300 determines a short circuit of the load when both of the sense current detection unit 100 and the voltage change detection unit 200 detect a short circuit. That is, a double check is performed for a short circuit. Even if the determination time is set shorter than the conventional filter time, noise tolerance can be guaranteed. Therefore, by adopting the drive device 12 according to the present embodiment, it is possible to reduce the filter time while preventing erroneous protection operation due to noise.

(Modification 2)
As the diode 240 shown in the second embodiment, a free-wheeling diode 242 (FWD242) attached to a predetermined IGBT cell (hereinafter referred to as a subcell 241) can be used. As shown in FIG. 10, the subcell 241 has a collector terminal connected in common with the collector terminal of the main cell 61, and an emitter terminal connected to the short-circuit detection unit 300. The emitter terminal corresponds to the SE2 terminal in the second embodiment. The FWD 242 has an anode terminal connected to the collector terminal of the subcell 241 and a cathode terminal connected to the emitter terminal of the subcell 241. The FWD 242 is configured to function as the diode 240 by connecting the gate terminal and the emitter terminal of the subcell 241 to each other. According to this, a well-known RC-IGBT (Reverse Conducting-IGBT) can be used as it is.

(Modification 3)
As in Modification 1 with respect to the first embodiment, the power switching element can be replaced with the MOS transistor 70 from the IGBT 60 in the second embodiment and Modification 2.

  As shown in FIG. 11, the MOS transistor 70 includes a main cell 71, a sense cell 150, and a diode 270, similar to the IGBT 60. The diode 270 includes a subcell 271 and an FWD272. The drive device 13 in this modification has a structure in which the main cell 61, the sense cell 140, and the diode 240 of the IGBT 60 are replaced with the main cell 71, the sense cell 150, and the diode 270 of the MOS transistor 70, respectively, in the second embodiment. doing. The drain terminals of the main cell 71, the sense cell 150, and the subcell 271 are connected in common. The main cell 71 and the sense cell 150 have a common gate terminal connected thereto. The FWD 272 has an anode terminal connected to the collector terminal of the subcell 271 and a cathode terminal connected to the emitter terminal of the subcell 271. The subcell 271 has a gate terminal and a source terminal connected to each other, and the FWD 272 functions as the diode 270. The source terminals of the main cell 71, the sense cell 150, and the subcell 271 correspond to the KE terminal, SE1 terminal, and SE2 terminal in the second embodiment, respectively.

  Since the driving device 13 in this modification is obtained by replacing the cells 61, 140, and 241 of the IGBT 60 with MOS transistors in the second embodiment, the sense cell 150 and the sense resistor 120 include the sense current detection unit 100. The diode 270, the pull-up power supply 250, and the pull-up resistor 260 constitute the voltage change detection unit 200. The configurations of the short circuit detection unit 300 and the control unit 400 are the same as those in the second embodiment.

  The operation and effect of the driving device 13 are the same as those of the driving device 12 in the second embodiment. Regarding the description of the second embodiment and the second modification, the collector current is the drain current, the collector terminal is the drain terminal, In other words, using the emitter terminal as the source terminal, the operational effects of the present modification can be described. Therefore, by adopting the driving device 13 according to this modification, it is possible to reduce the filter time while preventing erroneous protection operation due to noise.

(Other embodiments)
The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

  In the above-described embodiment, the example in which the IGBTs 20 and 60 and the MOS transistors 50 and 70 are driven as the power switching element has been described. However, the present invention is applicable to power switching elements other than these, and for example, a thyristor may be used.

  Further, in each of the above-described embodiments and modifications, an example in which each cell of the IGBT or the MOS transistor is formed on the same semiconductor substrate is shown, but each may be formed as an independent element.

DESCRIPTION OF SYMBOLS 10 ... Drive device, 20 ... IGBT (power switching element), 30 ... ON side circuit, 40 ... OFF side circuit, 100 ... Sense current detection part, 200 ... Voltage change detection part, 300 ... Short circuit detection part, 400 ... Control part

Claims (8)

A drive device for controlling on / off of a power switching element (20, 50, 60, 70),
A sense current detector (100) for detecting an output current of the power switching element;
A voltage change detector (200) for detecting a change in the output voltage of the power switching element;
A short-circuit detector (300) for determining a short-circuit of the power switching element according to input signals from the sense current detector and the voltage change detector;
The short circuit detection unit further determines whether or not there is a short circuit based on a predetermined change in the output voltage in a state where the output current exceeds a predetermined threshold. The voltage change detection unit detects a time change of the output voltage by configuring a differentiation circuit with a capacitor and a resistor (220),
The short circuit detection unit is configured such that the power switching element is in a short circuit state when an intermediate potential between the capacitor and the resistor becomes positive in a state where the output current exceeds a predetermined threshold. The drive device according to claim 1, wherein The power switching element is an insulated gate bipolar transistor (20), and includes a main cell (21) through which a collector current as the output current flows, and a subcell (210) as the voltage change detection unit,
In the subcell, the collector terminal is common to the main cell, the gate terminal and the emitter terminal are set to the same potential, and the internal capacitance of the power switching element constitutes a feedback capacitance as the capacitance,
The short-circuit detection unit determines that the power switching element is in a short-circuit state when the voltage of the emitter terminal in the subcell becomes positive in a state where the collector current exceeds a predetermined threshold. The drive device according to claim 2, wherein: The power switching element is a MOS transistor (50), and includes a main cell (51) through which a drain current as the output current flows, and a sub cell (230) as the voltage change detection unit,
In the subcell, the drain terminal is common to the main cell, the gate terminal and the source terminal are set to the same potential, and the internal capacitance of the power switching element constitutes a feedback capacitance as the capacitance,
The short-circuit detection unit determines that the power switching element is in a short-circuit state when a voltage at a source terminal in the subcell becomes positive in a state where the drain current exceeds a predetermined threshold. The drive device according to claim 2, wherein: The voltage change detection unit includes a diode (240, 270), a pull-up power source (250), and a pull-up resistor (260).
The diode has an anode terminal connected to a terminal on the upstream side of the output current,
The pull-up power supply is configured so that a terminal voltage VH on the upstream side of the output current, a voltage VB of the pull-up power supply, and a forward voltage Vf of the diode satisfy VB−Vf ≦ VH. Connected to the cathode terminal of the diode via a pull-up resistor,
In the state where the output current exceeds a predetermined threshold, the short circuit detection unit maintains the pull-up voltage longer than a predetermined determination time in the potential of the cathode terminal in the diode, The drive device according to claim 1, wherein the power switching element is determined to be in a short circuit state. The power switching element is an insulated gate bipolar transistor (60);
As the diode of the voltage change detection unit, an anode terminal has a free-wheeling diode (242) connected to a collector terminal in the power switching element,
The short-circuit detection unit maintains the pull-up voltage for a longer time than a predetermined determination time when the potential of the cathode terminal of the free-wheeling diode is in a state where a collector current as the output current exceeds a predetermined threshold. Accordingly, it is determined that the power switching element is in a short-circuit state. The power switching element is a MOS transistor (70),
As the diode of the voltage change detection unit, an anode terminal has a free-wheeling diode (272) connected to a drain terminal of the power switching element,
The short-circuit detection unit maintains the pull-up voltage for a longer time than a predetermined determination time when the potential of the cathode terminal of the free-wheeling diode is in a state where the drain current as the output current exceeds a predetermined threshold. Accordingly, it is determined that the power switching element is in a short-circuit state.   The driving apparatus according to claim 6 or 7, wherein the determination time is set to be equal to or longer than a time constant defined by an internal resistance of the power switching element and a parasitic inductance generated in the circuit.

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