Switching element control device

Abstract

To improve reliability of a switching element; and to improve detection accuracy of an over-current, in a switching element control device having an over-current protection function.SOLUTION: A switching element control device comprises: a drive circuit (2) for driving a switching element (1) according to a drive control signal (Vin); a first reference power supply (4) for outputting a first reference voltage; a reference voltage control part (5) for adjusting the first reference voltage by controlling the first reference power supply (4) in accordance with a reference voltage setting signal (Vs); and an over-current detection circuit (3) for outputting a first cutoff signal (Hoff), when an ON voltage of the switching element (1) becomes the first reference voltage or higher. The drive circuit (2) performs hard cutting-off of the switching element (1) according to the first cutoff signal (Hoff).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a control device for a switching element, and particularly to an overcurrent protection function of a switching element.

Background Art

[0002] There is known a switching element control device having an overcurrent protection function for protecting a switching element from overcurrent. For example, in Patent Document 1 below, it is determined whether a switching element is in an unsaturated state from the on-voltage of the switching element, and it is determined that the switching element in the unsaturated state is in an overcurrent state (for example, a short circuit), and the switching element is cut off. The overcurrent protection function of Patent Document 1 protects the switching element from a large current caused by a short circuit of a load or the like, and in order to suppress the generation of an excessive surge voltage due to di / dt and parasitic inductance L when cutting off the large current, "soft cutoff" is performed in which the switching element is turned off more slowly than normal operation. On the other hand, turning off the switching element at high speed (for example, at the same speed as normal operation) is called "hard cutoff".

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Compared with hard cutoff, soft cutoff of a switching element has a problem of a decrease in the reliability of the switching element because the time during which overcurrent flows becomes longer and the thermal stress due to the current becomes larger.

[0005] In addition, there are differences in specifications for each product and variations for each individual in the characteristics of switching elements. Therefore, in a method of detecting overcurrent (unsaturated state) from the on-voltage of a switching element, in order to prevent misdetection of the unsaturated state, a threshold value for determining whether it is in the unsaturated state is set to about 3 times (about 10 V) or more of the rated on-voltage. This means that even if an overcurrent exceeding the rating flows through the switching element, if the value is less than 3 times the rating, it will not be detected as an overcurrent, and the detection accuracy of the overcurrent is low. As a result, for an overcurrent less than 3 times the rating, the overcurrent protection function does not operate, stress is applied to the switching element, and in some cases, it may lead to the destruction of the switching element. Such an overcurrent may occur due to factors other than a short circuit, for example, when the load temporarily increases.

[0006] The present disclosure has been made to solve the above problems, and an object thereof is to improve the reliability of a switching element and the detection accuracy of an overcurrent in a switching element control device having an overcurrent protection function.

Means for Solving the Problems

[0007] The switching element control device according to the present disclosure includes a drive circuit that drives a switching element in response to a drive control signal, a first reference power supply that outputs a first reference voltage, and a reference voltage control unit that controls the first reference power supply in response to a reference voltage setting signal to adjust the first reference voltage, and an overcurrent detection circuit that outputs a first cutoff signal when the on-voltage of the switching element becomes equal to or higher than the first reference voltage, and the drive circuit performs a hard cutoff of the switching element in response to the first cutoff signal.

Effects of the Invention

[0008] According to the switching element control device according to the present disclosure, it is possible to improve the reliability of the switching element and the detection accuracy of the overcurrent.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0010] <Embodiment 1> FIG. 1 is a diagram showing the configuration of the switching element control device according to Embodiment 1. As shown in FIG. 1, the switching element control device controls the operation of the switching element 1 and includes a drive circuit 2, an overcurrent detection circuit 3, a first reference power source 4, and a reference voltage control unit 5.

[0011] In the present embodiment, it is assumed that the switching element 1 is an IGBT (Insulated Gate Bipolar Transistor). However, there is no restriction on the type of the switching element 1, and for example, a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), a bipolar transistor, or the like may be used. Also, the main material of the switching element 1 is most commonly silicon (Si), but for example, a wide bandgap semiconductor such as silicon carbide (SiC) or gallium nitride (GaN) may be used. When the material of the switching element 1 is a wide bandgap semiconductor, characteristics excellent for operation at high voltage, high current, and high temperature can be obtained as compared with the case of silicon.

[0012] The drive circuit 2 drives the switching element 1 according to the drive control signal Vin. Specifically, the drive circuit 2 switches on and off the switching element 1 by outputting a gate signal corresponding to the drive control signal Vin to the gate of the switching element 1.

[0013] The first reference power supply 4 outputs a first reference voltage. The first reference voltage output by the first reference power supply 4 is variable, and the value of the first reference voltage can be controlled by the reference voltage control unit 5. The reference voltage control unit 5 adjusts the first reference voltage output from the first reference power supply 4 according to the reference voltage setting signal Vs.

[0014] The overcurrent detection circuit 3 is connected to the collector of the switching element 1 and the first reference power supply 4, and the collector voltage of the switching element 1 and the first reference voltage are input to the overcurrent detection circuit 3. When the on-voltage of the switching element 1 (that is, the collector voltage when the switching element 1 is in the on state) becomes equal to or higher than the first reference voltage, the overcurrent detection circuit 3 determines that an overcurrent has occurred in the switching element 1, and outputs a hard cutoff signal Hoff, which is a first cutoff signal for cutting off the switching element 1. The hard cutoff signal Hoff output by the overcurrent detection circuit 3 is input to the drive circuit 2.

[0015] When the hard cutoff signal Hoff is input, the drive circuit 2 outputs a gate signal to turn off the switching element 1 regardless of the drive control signal Vin, and turns the switching element 1 into an off state (cutoff state), thereby protecting the switching element 1 from overcurrent.

[0016] The operation of the drive circuit 2 turning off the switching element 1 in response to the hard cutoff signal Hoff is hard cutoff. The turn-off speed in hard cutoff is, for example, the same as the turn-off speed during normal operation. When the drive circuit 2 performs hard cutoff of the switching element 1 when an overcurrent flows through the switching element 1, compared with the case of soft cutoff, the switching element 1 can be quickly protected from overcurrent, so the stress on the switching element 1 can be reduced and the reliability of the switching element 1 can be improved.

[0017] As can be understood from the above description, the first reference voltage output by the first reference power supply 4 serves as the threshold of the on-voltage of the switching element 1 for determining whether an overcurrent flows through the switching element 1. This first reference voltage can be adjusted using the reference voltage setting signal Vs input to the reference voltage control unit 5. Therefore, even if there are differences in product specifications or variations among individuals in the characteristics of the switching element 1, by adjusting the reference voltage setting signal Vs according to the product specifications and actual variations of the actually used switching element 1, the first reference voltage, which is the threshold, can be set to a value suitable for the on-voltage of the switching element 1. Thus, the first reference voltage can be set in a region less than three times the rated value (for example, in the range from 0V to 10V) to improve the detection accuracy of overcurrent.

[0018] Also, since the first reference voltage is set in a region less than three times the rated value, the overcurrent detection circuit 3 can detect the occurrence of overcurrent at an early stage. Therefore, even if the hard cutoff of the switching element 1 is performed, an excessive surge voltage may be suppressed. This also contributes to improving the reliability of the switching element 1. Note that the value of the first reference voltage may be appropriately adjusted according to requirements such as the actual usage conditions of the switching element 1 and the intention of safety design.

[0019] In the switching element control device of FIG. 1, the overcurrent detection circuit 3 is directly connected to the collector of the switching element 1. Such a connection can be achieved by configuring the overcurrent detection circuit 3 using a MOS transistor having a breakdown voltage equal to or higher than that of the switching element 1. Alternatively, the overcurrent detection circuit 3 may be configured using a high-voltage diode and a limiting resistor. In that case, it should be noted that the first reference voltage serving as the threshold cannot be set to be less than the forward voltage (VF) of the diode, and it is also necessary to consider the variations in the characteristics of the high-voltage diode and the limiting resistor.

[0020] In addition, as a method for the overcurrent detection circuit 3 to detect an overcurrent less than three times the rating of the switching element 1, there is also a method of inserting a shunt resistor into the current path of the switching element 1 and having the overcurrent detection circuit 3 detect the overcurrent from the voltage generated in the shunt resistor. However, this method has the demerit that power loss occurs in the shunt resistor even during normal operation.

[0021] As a means for suppressing the power loss of this shunt resistor method, there is also a method of providing a current sense terminal in the switching element 1 into which a part of the current flowing through the switching element 1 flows, and having the overcurrent detection circuit 3 detect the overcurrent from the current flowing through the current sense terminal. However, to adopt this method, it is necessary to increase the chip area of the switching element 1 by providing a structure for current sensing, increase the assembly process, add wiring patterns to the substrate on which the switching element 1 is mounted, etc., and it should be noted that the cost increases. In addition, the cost increase due to the increase in chip area becomes more prominent when a material with a high material cost such as silicon carbide (SiC) is used for the material of the switching element 1.

[0022] Conversely, as shown in FIG. 1, the configuration in which the overcurrent detection circuit 3 is directly connected to the collector of the switching element 1 is advantageous in terms of loss and cost.

[0023] <Embodiment 2> FIG. 2 is a diagram showing the configuration of a switching element control device according to Embodiment 2. The configuration of the switching element control device according to Embodiment 2 is obtained by adding a short-circuit detection circuit 6, a second reference power supply 7, a cutoff method selection circuit 8, and a soft cutoff circuit 9 to the configuration of Embodiment 1 (FIG. 1). Note that the configurations and operations of the switching element 1, drive circuit 2, overcurrent detection circuit 3, first reference power supply 4, and reference voltage control unit 5 shown in FIG. 2 may be basically the same as those in Embodiment 1, so the differences from Embodiment 1 will be described here, and descriptions overlapping with Embodiment 1 will be omitted.

[0024] The second reference power supply 7 outputs a second reference voltage. The second reference voltage is fixed at an on-voltage (i.e., 10 V or higher) that allows the switching element 1 to be regarded as in an unsaturated state in consideration of variations in the characteristics of the switching element 1. However, similar to the first reference power supply 4, the second reference power supply 7 may also be configured to be able to adjust the second reference voltage according to a signal input from the outside.

[0025] The short-circuit detection circuit 6 is connected to the collector of the switching element 1 and the second reference power supply 7, and the collector voltage of the switching element 1 and the second reference voltage are input to the short-circuit detection circuit 6. When the on-voltage of the switching element 1 becomes equal to or higher than the second reference voltage, the short-circuit detection circuit 6 determines that the load of the switching element 1 is in a short-circuit state, and outputs a soft cut-off signal Soff, which is a second cut-off signal for cutting off the switching element 1. Thus, the second reference voltage output by the second reference power supply 7 serves as a threshold value for the on-voltage of the switching element 1 to determine whether the load of the switching element 1 is in a short-circuit state.

[0026] On the other hand, the first reference voltage output by the first reference power supply 4 serves as a threshold value for determining whether an overcurrent has flowed through the switching element 1, similar to the first embodiment. Therefore, the first reference voltage is set by the reference voltage control unit 5 to be less than three times the rated value. That is, the first reference voltage is set to a value lower than the second reference voltage.

[0027] The soft cut-off circuit 9 performs soft cut-off of the switching element 1 according to the soft cut-off signal Soff output by the short-circuit detection circuit 6. However, as will be described below, the soft cut-off signal Soff is not directly input from the short-circuit detection circuit 6 to the soft cut-off circuit 9, but is input to the soft cut-off circuit 9 through the cut-off method selection circuit 8.

[0028] The hard cutoff signal Hoff output by the overcurrent detection circuit 3 and the soft cutoff signal Soff output by the short circuit detection circuit 6 are input to the cutoff method selection circuit 8. When only the hard cutoff signal Hoff is input to the cutoff method selection circuit 8, the hard cutoff signal Hoff is input to the drive circuit 2 to cause the hard cutoff of the switching element 1. Further, when only the soft cutoff signal Soff or both the hard cutoff signal Hoff and the soft cutoff signal Soff are input to the cutoff method selection circuit 8, the soft cutoff signal Soff is input to the soft cutoff circuit 9 to cause the soft cutoff of the switching element 1.

[0029] When the soft cutoff signal Soff is input from the cutoff method selection circuit 8, the soft cutoff circuit 9 performs the soft cutoff of the switching element 1. When the hard cutoff signal Hoff is input from the cutoff method selection circuit 8 to the drive circuit 2, the hard cutoff of the switching element 1 is performed. Since the overcurrent detection circuit 3 outputs the soft cutoff signal Soff when both the hard cutoff signal Hoff and the soft cutoff signal Soff are input, when the detection of an overcurrent by the overcurrent detection circuit 3 and the detection of a short circuit by the short circuit detection circuit 6 occur simultaneously, the soft cutoff of the switching element 1 is preferentially performed.

[0030] According to the switching element control device according to Embodiment 2, when an overcurrent less than three times the rated current flows through the switching element 1, the drive circuit 2 performs the hard cutoff of the switching element 1, suppressing the thermal stress and increased loss due to the overcurrent. Further, when a current of three times or more the rated current (an overcurrent due to a short circuit of the load) flows through the switching element 1, the soft cutoff circuit 9 performs the soft cutoff of the switching element 1, suppressing the generation of an excessive surge voltage. In this way, since an appropriate cutoff method according to the magnitude of the overcurrent flowing through the switching element 1 is implemented, the reliability of the switching element 1 can be further improved compared to Embodiment 1.

[0031] When the switching element control devices of Embodiments 1 and 2 cut off the switching element 1 to protect against overcurrent, they may output a fault signal FO to notify an abnormality to the system in which the switching element control device is incorporated. For example, in Embodiment 2, as shown in FIG. 2, the fault signal FO is configured to be output from the cutoff method selection circuit 8, and when the hard cutoff signal Hoff is input from the overcurrent detection circuit 3 to the cutoff method selection circuit 8 (that is, when an overcurrent less than three times the rated value is detected; hereinafter referred to as "when overcurrent is detected"), the fault signal FO is not output, and the fault signal FO is output only when the soft cutoff signal Soff is input from the second reference power supply 7 (that is, when a short circuit state of the load is detected; hereinafter referred to as "when short circuit is detected"). In that case, the system interrupts the normal operation when a short circuit is detected, but recognizes the normal state and continues the normal operation when an overcurrent is detected.

[0032] Generally, the switching element 1 is selected to have a rating larger than the current during steady operation in order to have a margin with respect to the maximum current in use considering the worst case (so-called overspec). When the system continues normal operation when an overcurrent is detected as described above, the current flowing through the switching element 1 is automatically suppressed to the set value. Therefore, as the switching element 1, one with a rating close to the current during steady operation can be used, leading to cost reduction.

[0033] Also, when the switching element 1 is an IGBT, since the IGBT has a built-in voltage, the steady loss in the low current region is large. Therefore, depending on the characteristics of the IGBT, it can also be expected that continuous steady operation even when an overcurrent near the rating of the IGBT occurs will lead to loss reduction.

[0034] It should be noted that the embodiments can be freely combined, or each embodiment can be appropriately modified or omitted.

[0035] <Supplementary Note> Hereinafter, aspects of the present disclosure will be summarized and described as supplementary notes.

[0036] (Appendix 1) A drive circuit that drives a switching element in response to a drive control signal, A first reference power supply that outputs a first reference voltage, A reference voltage control unit that adjusts the first reference voltage by controlling the first reference power supply in response to a reference voltage setting signal, An overcurrent detection circuit that outputs a first cutoff signal when the on-voltage of the switching element becomes equal to or higher than the first reference voltage, Comprising, The drive circuit performs a hard cutoff of the switching element in response to the first cutoff signal, Switching element control device.

[0037] (Appendix 2) The switching element is made of silicon carbide, The switching element control device according to Appendix 1.

[0038] (Appendix 3) A second reference power supply that outputs a second reference voltage, A short-circuit detection circuit that outputs a second cutoff signal when the on-voltage of the switching element becomes equal to or higher than the second reference voltage, A soft cutoff circuit that performs a soft cutoff of the switching element in response to the second cutoff signal, Receiving the first cutoff signal and the second cutoff signal, when only the first cutoff signal is input, input the first cutoff signal to the drive circuit to perform a hard cutoff of the switching element, and when only the second cutoff signal or both the first cutoff signal and the second cutoff signal are input, input the second cutoff signal to the soft cutoff circuit to perform a soft cutoff of the switching element A cutoff method selection circuit, Further comprising, The switching element control device according to Appendix 1 or Appendix 2.

[0039] (Appendix 4) The first reference voltage is set to a value lower than the second reference voltage, The switching element control device described in Supplementary Note 3.

[0040] (Supplementary Note 5) Output a fault signal when the second cutoff signal is output from the short-circuit detection circuit. The switching element control device described in Supplementary Note 3 or Supplementary Note 4.

Explanation of Signs

[0041] 1 Switching element, 2 Drive circuit, 3 Overcurrent detection circuit, 4 First reference power supply, 5 Reference voltage control unit, 6 Short-circuit detection circuit, 7 Second reference power supply, 8 Cutoff method selection circuit, 9 Soft cutoff circuit, Hoff Hard cutoff signal, Soff Soft cutoff signal, Vin Drive control signal, Vs Reference voltage setting signal, FO Fault signal.

Claims

1. A drive circuit that drives a switching element in response to a drive control signal, A first reference power supply that outputs a first reference voltage, A reference voltage control unit that adjusts the first reference voltage by controlling the first reference power supply in response to a reference voltage setting signal, An overcurrent detection circuit that outputs a first cutoff signal when the on-voltage of the switching element becomes equal to or higher than the first reference voltage, Comprising, The drive circuit performs a hard cutoff of the switching element in response to the first cutoff signal. A switching element control device.

2. The switching element is made of silicon carbide. The switching element control device according to Claim 1.

3. A second reference power supply that outputs a second reference voltage, A short-circuit detection circuit that outputs a second cutoff signal when the on-voltage of the switching element becomes equal to or higher than the second reference voltage, A soft cutoff circuit that performs a soft cutoff of the switching element in response to the second cutoff signal, Receiving the first cutoff signal and the second cutoff signal, when only the first cutoff signal is input, the first cutoff signal is input to the drive circuit to cause the hard cutoff of the switching element, and when only the second cutoff signal or both the first cutoff signal and the second cutoff signal are input, the second cutoff signal is input to the soft cutoff circuit to cause the soft cutoff of the switching element. A cutoff method selection circuit, Further comprising, The switching element control device according to Claim 1.

4. The first reference voltage is set to a value lower than the second reference voltage. The switching element control device according to Claim 3.

5. Outputs a fault signal when the second cutoff signal is output from the short-circuit detection circuit. The switching element control device according to Claim 3 or Claim 4.

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