JP2008141841A - Overcurrent protection circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem that it is difficult to properly detect an overcurrent immediately after the on-operation of a switching element SW when detecting the overcurrent by detecting a current flowing in the switching element SW by using a sense voltage. <P>SOLUTION: The sense voltage is applied to each non-inverting input terminal of an overcurrent comparator 43 and a penetration current comparator 44 via an RC filter circuit 42. Threshold voltages Vref1, Vref2 are applied to inverting input terminals of the overcurrent comparator 43 and the penetration current comparator 44. When a duration in which the sense voltage becomes the threshold voltage Vref1 or higher reaches a specified time Delay1 or longer, and when a duration in which the sense voltage becomes the threshold voltage Vref2 or higher reaches a specified time Delay2 or longer, the switching element SW is shut off. The specified time Delay2 and the threshold voltage Vref2 are set for a penetration current. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an overcurrent protection circuit that limits a current flowing through a voltage-driven switching element.

  As this type of protection circuit, for example, as shown in Patent Document 1 below, a minute current (sense current) output from the sense terminal of an insulated gate bipolar transistor (IGBT) as a switching element is correlated with the collector current of the IGBT. A protection circuit that detects the current flowing through the IGBT by utilizing the above has also been proposed. In the protection circuit, the current flowing through the IGBT is indirectly detected based on the voltage drop amount in the resistor connected between the sense terminal and the emitter. And it is judged whether the electric current which flows through IGBT is more than a threshold value by comparing the amount of voltage drops with a threshold voltage.

Further, in the above protection circuit, when the IGBT is shut off because the duration in which the current flowing through the IGBT is equal to or greater than the threshold is a specified time, a plurality of thresholds are set, and the specified time is set shorter as the threshold is larger. . This is a setting made in view of the fact that the allowable time for the current to flow becomes shorter as the current flowing to the IGBT becomes larger. With this setting, the IGBT can be shut off at an appropriate timing.
JP-A-5-292656

  By the way, for example, an inverter or the like has a configuration in which switching elements are connected in series. In this case, when the pair of switching elements are simultaneously turned on, the current flowing through the switching elements tends to be particularly large due to the current flowing therethrough. At this time, the rate of increase in the current flowing through the switching element tends to increase compared to when the single switching element is in the ON state. For this reason, if the allowable time and the threshold voltage are set based on a single switching element, it is not possible to appropriately deal with when a through current flows.

  Further, although the relationship between the sense current and the collector current is a unique relationship (substantially proportional relationship), the relationship immediately after the IGBT is turned on is different from the relationship in the stable state of the gate voltage. Has been found by the inventors. For this reason, if a threshold voltage corresponding to a short specified time is set based on the above relationship in the stable state of the gate voltage, the threshold voltage may not be appropriate immediately after the IGBT is turned on.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to detect a current flowing through a voltage-driven switching element based on a voltage drop amount of a resistor connected to the switching element. An object of the present invention is to provide an overcurrent protection circuit that can more appropriately limit the current flowing through the switching element.

  Hereinafter, means for solving the above-described problems and the operation and effects thereof will be described.

  In the first aspect of the present invention, the voltage drop amount of the resistor connected between the sense terminal and the output terminal that outputs a minute current correlated with the current between the input terminal and the output terminal of the switching element is the first. Overcurrent determination means for determining that an excessive current flows through the switching element when a continuation time that is equal to or greater than a threshold voltage is equal to or greater than a first specified time; and continuation that the voltage drop amount is equal to or greater than a second threshold voltage When the time is equal to or longer than the second specified time, the through current determining means for determining that a current passing through the switching element and the adjacent switching element flows, and determining that the penetrating current or the excessive current flows. And a blocking means for blocking the switching element, wherein the second specified time is set shorter than the first specified time. .

  In the said invention, it is judged that the through-current flowed because the duration for which the voltage drop amount is equal to or higher than the second threshold voltage is equal to or longer than the second specified time. By making the second specified time shorter than the first specified time, it is possible to appropriately cope with the through current. Then, by cutting off the switching element when it is determined that the through current has flowed, the amount of current flowing through the switching element can be reduced compared to the case of simply limiting the current of the switching element. The calorific value can be reduced.

  According to a second aspect of the present invention, in the first aspect of the invention, the second threshold voltage is a voltage drop amount immediately after the switching element is turned on with respect to a stable voltage of the conduction control terminal of the switching element. It is characterized by being set while compensating for the change.

  The relationship between the current flowing between the input terminal and the output terminal of the switching element and the voltage drop amount may be different between immediately after the switching element is turned on and when the voltage of the conduction control terminal is stable. Therefore, based on the relationship between the current flowing between the input terminal and the output terminal of the switching element and the current output from the sense terminal when the voltage of the conduction control terminal is stable, the second current corresponding to the threshold current for through current is determined. If the threshold voltage is set, the actual current when it is determined that the second threshold voltage is reached may not match the threshold current for the through current. In this respect, the above-described invention can avoid such a problem by setting the threshold voltage while compensating for the change in the amount of voltage drop immediately after the ON operation with respect to the stable voltage of the conduction control terminal.

  According to a third aspect of the present invention, there is provided a voltage drop amount and a threshold voltage of a sense terminal that outputs a minute current having a correlation with a current between an input terminal and an output terminal of the switching element and a resistor connected between the output terminals. And determining means for determining whether or not a current greater than or equal to a threshold value flows through the switching element, the threshold voltage being an ON operation of the switching element when the voltage of the conduction control terminal of the switching element is stable It is set while compensating for the change in the voltage drop immediately thereafter.

  The relationship between the current flowing between the input terminal and the output terminal of the switching element and the voltage drop amount may be different between immediately after the switching element is turned on and when the voltage of the conduction control terminal is stable. Therefore, based on the relationship between the current flowing between the input terminal and the output terminal of the switching element and the current output from the sense terminal when the voltage of the conduction control terminal is stable, the threshold voltage corresponding to the current threshold is set. Then, the actual current when it is determined that the threshold voltage is reached may not match the threshold current. In this respect, the above-described invention can avoid such a problem by setting the threshold voltage while compensating for the change in the amount of voltage drop immediately after the ON operation with respect to the stable voltage of the conduction control terminal.

  According to a fourth aspect of the present invention, in the third aspect of the present invention, the switching element is one of a plurality of switching elements connected in series, and the set threshold voltage is determined by the switching element. A threshold voltage corresponding to a maximum value among a plurality of thresholds having different values for the flowing current, and the determination means determines whether a current equal to or greater than one of the plurality of thresholds corresponds to the threshold. It is determined whether or not it flows for a specified time or more, and the specified time is set shorter as the threshold value is larger.

  When the switching elements are connected in series, a through current flows through these switching elements when two adjacent switching elements are simultaneously turned on. This through current tends to be larger than the current that flows when adjacent switching elements do not turn on at the same time. Moreover, when the through current flows, the rate of increase in current is greater than when the single switching element is in the on state. For this reason, excessive current may flow through the switching element unless the current flowing through the switching element is quickly limited when a through current flows.

  In this regard, in the above-described invention, by setting the specified time shorter as the threshold value is larger, it is possible to set a shorter specified time for the threshold value for determining the through current, that is, the larger threshold value, and thus the through current flows. This can be appropriately limited.

  According to a fifth aspect of the present invention, the threshold value includes a plurality of values having different values from each other, and is connected between the sense terminal and the output terminal that output a minute current having a correlation with the current between the input terminal and the output terminal of the switching element. Whether or not current more than one of the plurality of threshold values flows through the switching element for a specified time or more based on a comparison between a voltage drop amount of the resistor to be applied and a threshold voltage corresponding to each threshold value The threshold voltage is set by adding a margin to a value corresponding to the allowable current of the switching element, and the larger the threshold, the larger the margin is set. Features.

  When the switching elements are connected in series, a through current flows through these switching elements when two adjacent switching elements are simultaneously turned on. This through current tends to be larger than the current that flows when adjacent switching elements do not turn on at the same time. Moreover, when the through current flows, the rate of increase in current is greater than when the single switching element is in the on state. For this reason, excessive current may flow through the switching element unless the current flowing through the switching element is quickly limited when a through current flows. Therefore, it is desirable to determine whether or not a through current flows through the switching element based on a large threshold and a short specified time.

  On the other hand, the relationship between the current flowing between the input terminal and the output terminal of the switching element and the amount of voltage drop may be different between that immediately after the switching element is turned on and when the voltage of the conduction control terminal is stable. Therefore, based on the relationship between the current flowing between the input terminal and the output terminal of the switching element and the current output from the sense terminal when the voltage of the conduction control terminal is stable, the threshold voltage corresponding to the current threshold is set. Then, the actual current when it is determined that the threshold voltage has been reached immediately after the switching element is turned on may be smaller than the threshold current. In this respect, the above-described invention increases the margin for determining the threshold voltage as the threshold value increases, and sets the margin larger as the specified time is shorter. For this reason, it is possible to appropriately set a large threshold value corresponding to a short specified time which is a problem immediately after the switching element is turned on.

  The invention described in claim 6 is the invention described in claim 4 or 5, characterized in that the plurality of threshold values are two threshold values.

  In the above invention, by providing two threshold values, when the switching element is in the on state but the adjacent element is in the off state, when an excessive current flows, and when a through current flows through the adjacent switching element, Both can be dealt with appropriately.

  A seventh aspect of the invention is characterized in that, in the invention according to any one of the third to sixth aspects, the current flowing through the switching element is limited by shutting off the switching element.

  In the above configuration, when the current flowing through the switching element is equal to or higher than the threshold value, the power consumption can be reduced as much as possible in the situation where excessive current flows through the switching element by cutting off the switching element.

  The invention according to claim 8 is the invention according to any one of claims 2 to 7, further comprising filter means for filtering a voltage drop amount of the resistor, wherein the judging means outputs the output of the filter means to the It is characterized in that it is taken in as a voltage drop amount.

  Immediately after the switching element is turned on, noise is likely to be superimposed on the voltage drop, making it difficult to detect an accurate current. In this regard, in the above invention, by providing the filter means, the current flowing through the switching element can be accurately detected even immediately after the ON operation.

  Hereinafter, an embodiment in which an overcurrent protection circuit according to the present invention is applied to a high-voltage system of a hybrid vehicle will be described with reference to the drawings.

  FIG. 1 shows the overall configuration of a motor generator control system according to this embodiment.

  As shown in the figure, an inverter 12 is connected to three phases (U phase, V phase, and W phase) of the motor generator 10. The inverter 12 is a three-phase inverter, and appropriately applies the voltage of the high voltage battery 14 to the three phases of the motor generator 10. Specifically, the inverter 12 switches the switching elements SW1 and SW2 (U-phase arm) and the switching elements SW3 and SW4 (V-phase arm) so that each of the three phases is electrically connected to the positive electrode side or the negative electrode side of the high-voltage battery 14. It comprises a parallel connection body with switching elements SW5 and SW6 (W-phase arm). A connection point for connecting switching element SW <b> 1 and switching element SW <b> 2 in series is connected to the U phase of motor generator 10. Further, a connection point for connecting switching element SW3 and switching element SW4 in series is connected to the V phase of motor generator 10. Furthermore, a connection point for connecting switching element SW5 and switching element SW6 in series is connected to the W phase of motor generator 10. Incidentally, these switching elements SW1 to SW6 are constituted by insulated gate bipolar transistors (IGBT) in this embodiment. The inverter 12 includes flywheel diodes D1 to D6 connected in antiparallel to the switching elements SW1 to SW6.

  The switching elements SW <b> 1 to SW <b> 6 are operated by a microcomputer (microcomputer 20) using the low voltage battery 18 as a power source via the driver unit 16. FIG. 2 shows a component related to driving of one of the switching elements SW1 to SW6 (hereinafter referred to as switching element SW) in the driver unit 16.

  As illustrated, the driver unit 16 includes a drive circuit 30 and a protection circuit 40 for driving the switching element SW.

  The drive circuit 30 includes a driver 31 that applies a voltage to the conduction control terminal (gate) of the switching element SW. The driver 31 is a serial connection body of a P-channel transistor 31p and an N-channel transistor 31n. Capacitors 32 are connected to both ends of the driver 31. A drive voltage generation circuit 33 is connected between both electrodes of the capacitor 32. The drive voltage generation circuit 33 generates a voltage to be applied to the driver 31.

  In the drive voltage generation circuit 33, a power source 33b and a capacitor 33c are connected in parallel to the primary side of the transformer 33a, and a switching element 33d that connects and disconnects the transformer 33a, the power source 33b, and the capacitor 33c is provided. ing. The output voltage on the secondary side of the transformer 33a is applied to the capacitor 32 via the diode 33e.

  The driver 31 is driven in response to a switching command signal from the microcomputer 20. Specifically, it is driven by a switching command signal whose power is converted by the photocoupler 34 and the driving IC 35. In the driving IC 35, when the switching command is an on command, the P channel transistor 31p is turned on and the N channel transistor 31n is turned off. On the other hand, when the switching command is an off command, the P-channel transistor 31p is turned off and the N-channel transistor 31n is turned on. Thus, when the switching element SW is commanded to be turned on, the voltage of the capacitor 32 is applied to the gate G of the switching element SW, and when the switching element SW is commanded to be off, the gate G of the switching element SW is set to the same potential as the emitter E.

  The switching element SW includes a sense terminal ST that outputs a minute current (sense current) having a correlation with a current (collector current) flowing between the collector C and the emitter E. The sense terminal ST is connected to the protection circuit 40.

  The protection circuit 40 includes a resistor (sense resistor 41), and connects the sense terminal ST to the emitter E via the sense resistor 41. The amount of voltage drop (sense voltage) due to the sense resistor 41 is determined according to the sense current. Therefore, as shown by a solid line in FIG. 3, the sense voltage is determined by the current (collector current Ic) flowing through the switching element SW.

  An RC filter circuit 42 including a resistor 42a and a capacitor 42b is connected to the sense resistor 41 in parallel. The RC filter circuit 42 is means for removing noise superimposed on the sense voltage immediately after the switching element SW is turned on. The voltage across the sense resistor 41, that is, the sense voltage is applied to the non-inverting input terminals of the overcurrent comparator 43 and the through current comparator 44 via the RC filter circuit 42. Two different threshold voltages Vref1 and Vref2 are applied to the inverting input terminals of the overcurrent comparator 43 and the through current comparator 44, respectively. Thereby, the output signal of the overcurrent comparator 43 becomes logic “H” when the sense voltage becomes equal to or higher than the threshold voltage Vref1, and the output signal of the through current comparator 44 indicates that the sense voltage becomes equal to or higher than the threshold voltage Vref2. As a result, the logic becomes “H”.

  The output signal of the overcurrent comparator 43 is taken into the timer latch 45. The timer latch 45 outputs a signal of logic “H” when the duration time during which the output signal of the overcurrent comparator 43 becomes logic “H” reaches a specified time Delay 1 (for example, “4 to 5 μs”). On the other hand, the output signal of the through current comparator 44 is taken into the timer latch 46. The timer latch 46 outputs a signal of logic “H” when the duration time during which the output signal of the through current comparator 44 becomes logic “H” reaches a specified time Delay2 (<Delay, for example, “0 to 4 μs”). .

  The OR circuit 47 outputs a logical sum signal of the output signals of the timer latches 45 and 46 to the cutoff command circuit 48. The shutoff command circuit 48 operates the drive IC 35 and the soft shutoff circuit 49 when the output signal of the OR circuit 47 is logic “H”. The soft shut-off circuit 49 includes an N-channel transistor that conducts and shuts off between the gate G and the emitter E of the switching element SW via the resistor 50. In the shutoff command circuit 48, when the output signal of the OR circuit 47 is logic “H”, both the P channel transistor 31p and the N channel transistor 31n of the driver 31 are forcibly turned off by operating the drive circuit IC. At the same time, the N-channel transistor of the soft cutoff circuit 49 is turned on. As a result, by adjusting the resistance value of the resistor 50, the switching is performed more gently than when the switching element SW is switched from the on state to the off state in accordance with the switching off command from the microcomputer 20. This is a setting made in view of the possibility that the surge voltage may become excessively high if the switching element is switched to the OFF state at the same speed as that in the normal state when a larger current flows than in the normal state.

  According to such a configuration, when the duration when the sense voltage becomes the threshold voltage Vref1 is equal to or longer than the specified time Delay1, or when the duration when the sense voltage becomes the threshold voltage Vref2 is equal to or longer than the specified time Delay2, the switching element SW is turned on. It can be forcibly set to an off state (blocking state).

  The through current comparator 44 detects and copes with when a through current flows through the pair of switching elements connected in series when both switching elements SW of the arm of the inverter 12 are turned on. belongs to. On the other hand, the overcurrent comparator 43 detects when an excessive current flows through the switching element SW when one switching element SW of the arm of the inverter 12 is on. It is for coping. Here, when the through current flows through the switching element SW, the rate of increase in current is greater than when the through current does not flow. For this reason, when a through current flows, it is desired to detect this quickly and shut off the switching element SW.

  For this reason, the specified time Delay2 for through current is set shorter than the specified time Delay1 for overcurrent. In addition, when a through current flows, the current flowing through the switching element SW is particularly larger than normal, so the current threshold Ith2 (corresponding to the threshold voltage Vref2) for determining the through current is a pair of switching It is set larger than the current threshold value Ith1 (corresponding to the threshold voltage Vref1) when one of the elements SW is in the ON state. These threshold values Ith1 and Ith2 are set by adding a margin to the allowable current of the switching element SW.

  FIG. 4 shows an aspect of overcurrent protection according to the present embodiment when both of the pair of switching elements SW connected in series are in the on state and when one of them is in the on state.

  In the figure, Case 1 shows the behavior of current when the switching element SW is turned off by the protection circuit 40 when one of the pair of switching elements SW connected in series is in the on state. As shown in the drawing, the switching element SW is cut off when the duration time during which the collector current is equal to or greater than the threshold value Ith1 reaches the specified time Delay1. As a result, the collector current decreases.

  On the other hand, Case 2 shows the behavior of current when the switching element SW is turned off by the protection circuit 40 when a through current flows through a pair of switching elements SW connected in series. As shown in the figure, in this case, the collector current increases rapidly. And switching element SW is interrupted | blocked because the continuation time when collector current becomes more than threshold value Ith2 becomes the regulation time Delay2. As a result, the collector current decreases.

  Thus, by shortening the specified time Delay2 for through current, it is possible to appropriately cope with the through current.

  By the way, if the threshold voltage Vref2 for through current is the sense voltage (Vs1) when the collector current becomes the threshold value Ith2 in the relationship shown by the solid line in FIG. 3, the collector current Ic becomes the threshold value Ith2. The time cannot be judged properly. This is the relationship indicated by the solid line in FIG. 3 when the gate voltage of the switching element SW is stable, and the relationship immediately after the ON operation of the switching element SW when the sense resistor 41 is large ( This is because it is different from FIG. That is, immediately after the switching element SW is turned on, the sense voltage when the collector current Ic becomes the threshold value Ith2 is the voltage Vs2.

  FIG. 5 shows the behavior of the sense voltage associated with the ON operation of the switching element SW. Specifically, FIG. 5A shows the transition of the gate voltage (more precisely, the voltage Vge between the emitter and the gate), FIG. 5B shows the transition of the sense voltage, and FIG. The transition of the sense voltage after the filtering process by the RC filter circuit 42 is shown, and FIG. 5D shows the transition of the collector-emitter voltage Vce and the collector current Ic. FIG. 5E shows the static characteristics of the voltage Vge between the emitter and the gate of the switching element SW, the voltage Vce between the emitter and the collector, and the collector current Ic.

  As shown in the figure, when the switching element SW is turned on at time t1, the gate voltage rises. Then, when the gate voltage exceeds the threshold voltage Vth at time t2, the switching element SW is turned on, and the collector current Ic increases. As a result, the sense voltage also increases. However, the gate voltage once stagnates in an intermediate voltage state before the voltage Vg_on applied to the gate of the switching element SW (time t3 to t4). This stagnation period is a known mirror period. Thereafter, the gate voltage rises and becomes the voltage Vg_on applied to the gate at time t5.

  When the gate voltage exceeds the threshold voltage Vth, the collector current Ic increases to the final current value when the gate voltage becomes the voltage Vg_on. However, as shown in the figure, immediately after the ON operation of the switching element SW, the sense voltage changes despite the collector current Ic being constant. This is due to the following reason.

  When the switching element SW operates along the static characteristic, the collector current Ic flowing through the switching element SW is determined by the intersection of the load line determined by the resistance value downstream of the emitter and the static characteristic curve shown in FIG. The voltage Vce between the collector and the emitter is determined. However, immediately after the switching element SW is turned on, the decrease in the voltage Vce between the collector and the emitter is delayed with respect to the increase in the collector current Ic, and the switching element SW operates in the saturation region. That is, when the gate voltage reaches the threshold voltage Vth, the collector current Ic increases rapidly, and settles to a predetermined value, for example, at about time t3. At this time, the voltage Vce between the collector and the emitter hardly decreases. Note that the operating point of the switching element SW when the gate voltage becomes steady is set in the non-saturation region.

  On the other hand, the sense terminal is shown in FIG. 5E between the voltage between the gate of the switching element and the sense terminal, the voltage between the collector of the switching element and the sense terminal, and the sense current output from the sense terminal. Static characteristics similar to those of the above are established. However, in this embodiment, since the sense resistor 41 having a large resistance value is used, the voltage between the collector and the sense terminal and the sense current change substantially along the load line by the sense resistor 41. For this reason, as the collector current Ic increases, the sense current also increases, and the voltage between the collector and the sense terminal decreases.

  However, as described above, the voltage Vce between the collector and the emitter hardly changes until the time t3 when the collector current Ic becomes a steady state. On the other hand, until time t3, the gate voltage increases, and the potential of the sense terminal rises with respect to the potential of the emitter. The sense voltage at this time is higher than the sense voltage determined from the relationship between the collector current and the stable gate voltage shown by the solid line in FIG. This is a mechanism for a temporary rise in the sense voltage.

  Since the sense voltage temporarily rises in this way, the threshold voltage Vref2 cannot be determined based on the relationship when the gate voltage is stabilized as shown by the solid line in FIG. 3 and the threshold Ith2 for through current. However, this rise can be suppressed by reducing the resistance value of the sense resistor 41, but in such a case, the sense voltage decreases. For this reason, there is a concern that inconveniences such as a reduction in resistance to noise and a need to amplify before inputting a sense voltage to the overcurrent comparator 43 and the through current comparator 44 may occur. Therefore, in the present embodiment, the threshold voltage Vref2 is set to the previous value so that a through-current does not erroneously flow due to the rise of the sense voltage while the resistance value of the sense resistor 41 is set high (for example, several kΩ). A value larger than the value determined by the relationship shown in FIG. 2 and the through current threshold Ith2 is set (FIG. 5C). Thereby, it is possible to appropriately determine whether or not a through current has flowed.

  In order to appropriately determine the through current, it is desirable to determine the through current until the gate voltage is stabilized. More desirably, the through current is determined by the end of the mirror period. From such a viewpoint, the specified time Delay2 is set. Here, for example, the specified time Delay2 may be set to a length equal to or shorter than the mirror period.

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

  (1) When the duration when the sense voltage is equal to or higher than the threshold voltage Vref2 is equal to or longer than the specified time Delay2, it is determined that a current passing through the pair of switching elements SW flows, and the duration when the sense voltage becomes equal to or higher than the threshold voltage Vref1 When the specified time Delay1 or longer, it was determined that an excessive current flows when the single switching element SW of the arm is in the ON state. When any of the above determinations was made, the switching element SW was shut off. Thereby, it is possible to appropriately cope with the through current.

  (2) The threshold voltage Vref2 is set while compensating for the change in the sense voltage immediately after the ON operation of the switching element SW with respect to the stable voltage of the gate of the switching element SW. Thereby, the threshold voltage Vref2 can be set appropriately.

  (3) The current flowing through the switching element SW is limited by blocking the switching element SW. Thereby, the power consumption can be reduced as much as possible in a situation where an excessive current flows through the switching element SW.

  (4) By providing the RC filter circuit 42, the current flowing through the switching element SW can be accurately detected even immediately after the switching element SW is turned on.

  (5) The switching element SW is set so that its operating point is in the non-saturated region. Thereby, after the voltage of the gate of the switching element is stabilized, the operation can be performed in the non-saturation region.

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

  The relationship between the sense voltage and the collector current Ic actually changes according to the temperature of the switching element SW. For this reason, the threshold voltages Vref1 and Vref2 may be variably set according to the temperature of the switching element SW.

  In the above embodiment, in order to limit the through current caused by turning on both of the pair of switching elements SW connected in series and the excessive current when only one of the switching elements SW is turned on, Although the threshold voltages Vref1 and Vref2 and the specified times Delay1 and Delay2 are set, the present invention is not limited to this. For example, as can be seen in Patent Document 1 above, in view of the relationship between the current allowed for the switching element SW and the allowable time during which the current flows, the allowable time decreases as the allowable current increases. As shown in FIG. 6A, three or more threshold values and a prescribed time may be set. Even in this case, immediately after the switching element is turned on, while the gate voltage becomes the final applied voltage and is not stable, the sense voltage becomes higher than the value determined by the relationship shown in FIG. Therefore, as shown in FIG. 6B, for a short specified time, the threshold voltage is increased so as to compensate for the difference between the voltage determined by the relationship shown in FIG. 2 and the actual sense voltage. It is desirable to set.

  Even without using the shutoff command circuit 48 and the soft shutoff circuit 49, the switching element SW can be shut off by changing the switching command to an off command when a through current or excessive current flows.

  -A circuit including switching elements connected in series is not limited to an inverter. For example, a synchronous rectification type DC-DC converter may be used.

  -In addition to a pair of switching elements connected in series, a sense voltage is used to detect a current that flows immediately after the switching element is turned on, and to protect the switching element from an overcurrent based on this, the sense voltage It is effective to apply the present invention when setting the threshold voltage to be compared.

The figure which shows the whole structure of the control system of the motor generator concerning one Embodiment. The figure which shows the internal structure of the driver unit of the embodiment. The figure which shows the relationship between a sense voltage and collector current. The time chart which shows the aspect of protection from the overcurrent concerning the said embodiment. 4 is a time chart showing the behavior of the sense voltage according to the embodiment. The figure which shows the setting aspect of the threshold voltage in the modification of the said embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 41 ... Sense resistor, 42 ... RC filter circuit, 43 ... Overcurrent comparator, 44 ... Through current comparator, 45, 46 ... Timer latch, SW ... Switching element.

Claims (8)

In an overcurrent protection circuit for limiting a current flowing through a switching element of a voltage drive type that is any one of a plurality of switching elements connected in series with each other,
Sense terminal for outputting a minute current having a correlation with the current between the input terminal and the output terminal of the switching element, and a duration for which the voltage drop amount of the resistor connected between the output terminals is equal to or higher than the first threshold voltage. Overcurrent determination means for determining that an excessive current flows through the switching element when the first specified time or longer is reached;
A through current judging means for judging that a current passing through the switching element and a switching element adjacent to the switching element flows when a duration time in which the voltage drop amount becomes a second threshold voltage or more is a second specified time or more; ,
When it is determined that the current passing through or the excessive current flows, a blocking means for blocking the switching element,
The overcurrent protection circuit, wherein the second specified time is set shorter than the first specified time.   The second threshold voltage is set while compensating for a change in the amount of voltage drop immediately after an ON operation of the switching element with respect to a stable voltage of a conduction control terminal of the switching element. The overcurrent protection circuit according to Item 1. In the overcurrent protection circuit that limits the flowing current when the current flowing through the voltage-driven switching element is equal to or greater than the threshold
Based on a comparison between a sense terminal that outputs a minute current having a correlation with a current between an input terminal and an output terminal of the switching element and a voltage drop amount of a resistor connected between the output terminals and a threshold voltage, the switching element A determination means for determining whether or not a current of a threshold value or more flows,
The overcurrent protection circuit, wherein the threshold voltage is set while compensating for a change in the voltage drop immediately after the switching element is turned on with respect to a stable voltage of the conduction control terminal of the switching element. . The switching element is one of a plurality of switching elements connected in series,
The set threshold voltage is a threshold voltage corresponding to a maximum value of a plurality of thresholds having different values for the current flowing through the switching element;
The determination means determines whether or not a current greater than or equal to the plurality of threshold values flows through the switching element for a specified time or more according to the threshold value,
4. The overcurrent protection circuit according to claim 3, wherein the specified time is set shorter as the threshold value is larger. In an overcurrent protection circuit that limits a current that flows when a current flowing through the switching element is equal to or greater than a threshold for a voltage-driven switching element that is any one of a plurality of switching elements connected in series with each other ,
The threshold comprises a plurality having different values,
Comparison between a sense terminal that outputs a minute current having a correlation with a current between an input terminal and an output terminal of the switching element, and a voltage drop amount of a resistor connected between the output terminals and a threshold voltage corresponding to each threshold value And a determination means for determining whether or not a current greater than or equal to the plurality of threshold values flows through the switching element for a specified time or more according to the threshold value,
Each threshold voltage is set by adding a margin to a value corresponding to the allowable current of the switching element,
The overcurrent protection circuit, wherein the margin is set larger as the threshold value is larger.   6. The overcurrent protection circuit according to claim 4, wherein the plurality of threshold values are two threshold values.   The overcurrent protection circuit according to claim 3, wherein the current flowing through the switching element is limited by cutting off the switching element. A filter means for filtering a voltage drop amount of the resistor;
The overcurrent protection circuit according to claim 2, wherein the determination unit takes in an output of a filter unit as the voltage drop amount.

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