Switching element control device

Abstract

The purpose of the present invention is to improve the reliability of a switching element and the detection accuracy of overcurrent in a switching element control device having an overcurrent protection function. This switching element control device is provided with: a drive circuit (2) that drives a switching element (1) on the basis of a drive control signal (Vin); a first reference power supply (4) that outputs a first reference voltage; a reference voltage control unit (5) that adjusts the first reference voltage by controlling the first reference power supply (4) on the basis of the reference voltage setting signal (Vs); and an overcurrent detection circuit (3) that outputs a first OFF signal (Hoff) when the ON voltage of the switching element (1) becomes greater than or equal to a first reference voltage. The drive circuit (2) performs hard cutoff of the switching element (1) in accordance with the first cutoff signal (Hoff).

Description

Technical Field

[0001] The present invention 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 damage. For example, Patent Document 1 below discloses a switching element control device that determines whether a switching element is in an unsaturated state based on the on-voltage of the switching element, and determines that the switching element in the unsaturated state is in an overcurrent state (e.g., short circuit) and cuts off the switching element. The overcurrent protection function of Patent Document 1 protects the switching element from large current damage caused by a short circuit of a load or the like, and in order to suppress an excessive surge voltage generated due to di / dt and parasitic inductance L when cutting off a large current, performs "soft cut-off" in which the switching element is cut off more slowly than normal operation. In contrast, a "hard cut-off" is called when the switching element is cut off at high speed (e.g., at the same speed as normal operation).

[0003] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2001-8492

[0004] Compared with the hard cut-off of the switching element, the time during which overcurrent flows is longer in the soft cut-off of the switching element, and accordingly, the thermal stress caused by the current becomes larger. Therefore, the soft cut-off of the switching element has a problem of reduced reliability of the switching element.

[0005] In addition, there are differences in specifications for each product and fluctuations for each individual in the characteristics of the switching element. Therefore, in the method of detecting overcurrent (unsaturated state) based on the on-voltage of the switching element, for the purpose of preventing misdetection of the unsaturated state, in order to determine whether it is in the unsaturated state, the threshold value is set to be about 3 times or more of the rated on-voltage (about 10V). This means that even if an overcurrent greater than or equal to the rated value flows through the switching element, as long as its value is less than 3 times the rated value, the overcurrent cannot be detected, and the detection accuracy of the overcurrent is low. As a result, for an overcurrent less than 3 times the rated value, the overcurrent protection function does not operate, which puts pressure on the switching element and may sometimes cause damage to the switching element in some cases. Such an overcurrent sometimes occurs due to reasons other than a short circuit, such as a temporary increase in the load. Summary of the Invention

[0006] The present invention has been proposed to solve the above-described 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.

[0007] The switching element control device according to the present invention includes: a drive circuit that drives a switching element according to a drive control signal; a first reference power supply that outputs a first reference voltage; a reference voltage control unit that controls the first reference power supply according to a reference voltage setting signal, thereby adjusting the first reference voltage; and an overcurrent detection circuit that outputs a first cut-off signal if the on-voltage of the switching element becomes greater than or equal to the first reference voltage, and the drive circuit performs hard cut-off of the switching element according to the first cut-off signal.

[0008] Effects of the Invention

[0009] According to the switching element control device of the present invention, it is possible to improve the reliability of the switching element and the detection accuracy of overcurrent. Description of the Drawings

[0010] Figure 1 It is a diagram showing the structure of the switching element control device according to Embodiment 1.

[0011] Figure 2 It is a diagram showing the structure of the switching element control device according to Embodiment 2. Detailed Embodiments

[0012] <Embodiment 1>

[0013] Figure 1 It is a diagram showing the structure of the switching element control device according to Embodiment 1. As Figure 1 shown, 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 supply 4, and a reference voltage control unit 5.

[0014] In the present embodiment, the switching element 1 is an IGBT (Insulated Gate Bipolar Transistor). However, the type of the switching element 1 is not limited, and for example, it may also be a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), a bipolar transistor, etc. In addition, the main material of the switching element 1 is most often silicon (Si), but for example, it may also be a wide-bandgap semiconductor such as silicon carbide (SiC) or gallium nitride (GaN). When the material of the switching element 1 is a wide-bandgap semiconductor, compared with the case of silicon, it has excellent characteristics in operation at high voltage, high current, and high temperature.

[0015] The drive circuit 2 drives the switching element 1 according to the drive control signal Vin. Specifically, the drive circuit 2 outputs a gate signal corresponding to the drive control signal Vin to the gate of the switching element 1, thereby switching the on and off states of the switching element 1.

[0016] 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.

[0017] The overcurrent detection circuit 3 is connected to the collector of the switching element 1 and the first reference power supply 4, and inputs the collector voltage of the switching element 1 and the first reference voltage to the overcurrent detection circuit 3. If the on-voltage of the switching element 1 (i.e., the collector voltage when the switching element 1 is in the on state) becomes greater than or equal to the first reference voltage, the overcurrent detection circuit 3 determines that an overcurrent has occurred in the switching element 1 and outputs a first cut-off signal, i.e., a hard cut-off signal Hoff, for cutting off the switching element 1. The hard cut-off signal Hoff output by the overcurrent detection circuit 3 is input to the drive circuit 2.

[0018] If the drive circuit 2 is input with the hard cut-off signal Hoff, it outputs a gate signal that turns off the switching element 1 regardless of the drive control signal Vin, causing the switching element 1 to enter the off state (cut-off state), thereby protecting the switching element 1 from overcurrent damage.

[0019] The operation of the drive circuit 2 to cut off the switching element 1 according to the hard cut-off signal Hoff is hard cut-off. The cut-off speed of the hard cut-off is, for example, the same as the cut-off speed during normal operation. When an overcurrent flows through the switching element 1 and the drive circuit 2 performs hard cut-off of the switching element 1, compared with the case of soft cut-off, the switching element 1 can be quickly protected from overcurrent damage, so the stress on the switching element 1 can be reduced and the reliability of the switching element 1 is improved.

[0020] As described above, the first reference voltage output by the first reference power source 4 is the threshold value 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 the product specifications of the switching element 1 in terms of products and fluctuations in terms of individuals, the reference voltage setting signal Vs can be adjusted according to the product specifications and the actual fluctuations of the switching element 1 in actual use, so that the threshold value, that is, the first reference voltage, can be set to a value suitable for the on-voltage of the switching element 1. Thus, by setting the first reference voltage in the region less than three times the rated value (for example, in the range of 0V to 10V), the detection accuracy of the overcurrent can be improved.

[0021] In addition, by setting the first reference voltage in the region less than three times the rated value, the overcurrent detection circuit 3 can detect the generation of an overcurrent at an early stage. Therefore, even if a hard cut-off of the switching element 1 is performed, it is possible to suppress an excessive surge voltage. This also contributes to improving the reliability of the switching element 1. In addition, the value of the first reference voltage can be appropriately adjusted, for example, according to the actual use conditions of the switching element 1, the intention of the safety design, and other requirements.

[0022] In Figure 1 In the switching element control device, the overcurrent detection circuit 3 is directly connected to the collector of the switching element 1. By using a MOS transistor having a breakdown voltage greater than or equal to that of the switching element 1 to form the overcurrent detection circuit 3, such a connection can be achieved. Alternatively, the overcurrent detection circuit 3 can also be formed using a high-voltage diode and a limiting resistor. However, in this case, it should be noted that the threshold value, that is, the first reference voltage, cannot be set to be less than or equal to the forward voltage (VF) of the diode, and the fluctuations in the characteristics of the high-voltage diode and the limiting resistor also need to be considered.

[0023] In addition, as a method for the overcurrent detection circuit 3 to detect an overcurrent less than three times the rated value of the switching element 1, there is also the following method, that is, a shunt resistor is inserted into the current path of the switching element 1, and the overcurrent detection circuit 3 detects the overcurrent based on the voltage generated on the shunt resistor. However, this method has the disadvantage of generating power loss due to the shunt resistor during normal operation.

[0024] As a method for suppressing power loss in this shunt resistor method, there is also the following method. That is, a current sensing terminal is provided in the switching element 1, and the overcurrent detection circuit 3 detects an overcurrent based on the current flowing through the current sensing terminal. Among them, a part of the current flowing through the switching element 1 flows into the current sensing terminal. However, it should be noted that in order to adopt this method, it is necessary to realize an increase in the chip area of the switching element 1 due to the provision of the current sensing structure, an increase in the assembly process, an additional wiring pattern on the substrate on which the switching element 1 is mounted, etc., resulting in a cost increase. In addition, when a material with a high material cost such as silicon carbide (SiC) is used for the switching element 1, the cost increase due to the increase in the chip area becomes more significant.

[0025] On the contrary, as Figure 1 shown, the structure 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.

[0026] <Embodiment 2>

[0027] Figure 2 is a diagram showing the structure of the switching element control device according to Embodiment 2. The structure 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 cut-off method selection circuit 8, and a soft cut-off circuit 9 to the structure of Embodiment 1 ( Figure 1 ). In addition, Figure 2 it is sufficient that the structures and operations of the switching element 1, the drive circuit 2, the overcurrent detection circuit 3, the first reference power supply 4, and the reference voltage control unit 5 shown are basically the same as those in Embodiment 1. Therefore, the differences from Embodiment 1 will be described here, and the descriptions overlapping with Embodiment 1 will be omitted.

[0028] The second reference power supply 7 outputs a second reference voltage. The second reference voltage is fixed to a turn-on voltage (i.e., greater than or equal to 10V) that can be regarded as the switching element 1 being in an unsaturated state in consideration of fluctuations in the characteristics of the switching element 1. However, similar to the first reference power supply 4, the second reference power supply 7 can also be configured to be able to adjust the second reference voltage according to a signal input from the outside.

[0029] 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. If the turn-on voltage of the switching element 1 is greater than or equal to 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 second cut-off signal for cutting off the switching element 1, that is, a soft cut-off signal Soff. In this way, the second reference voltage output by the second reference power supply 7 is a threshold value of the turn-on voltage of the switching element 1 for determining whether the load of the switching element 1 is in a short-circuit state.

[0030] On the other hand, similar to Embodiment 1, the first reference voltage output by the first reference power supply 4 is a threshold value for determining whether an overcurrent flows through the switching element 1. Therefore, the first reference voltage is set to be less than three times the rated value by the reference voltage control unit 5. That is, the first reference voltage is set to a value lower than the second reference voltage.

[0031] 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.

[0032] The hard cut-off signal Hoff output by the overcurrent detection circuit 3 and the soft cut-off signal Soff output by the short-circuit detection circuit 6 are input to the cut-off method selection circuit 8. When only the hard cut-off signal Hoff is input to the cut-off method selection circuit 8, the hard cut-off signal Hoff is input to the drive circuit 2 to perform hard cut-off of the switching element 1. In addition, when only the soft cut-off signal Soff is input to the cut-off method selection circuit 8, or when both the hard cut-off signal Hoff and the soft cut-off signal Soff are input, the soft cut-off signal Soff is input to the soft cut-off circuit 9 to perform soft cut-off of the switching element 1.

[0033] If the soft cut-off signal Soff is input to the soft cut-off circuit 9 from the cut-off method selection circuit 8, the soft cut-off circuit 9 performs soft cut-off of the switching element 1. If the hard cut-off signal Hoff is input to the drive circuit 2 from the cut-off method selection circuit 8, the drive circuit 2 performs hard cut-off of the switching element 1. The overcurrent detection circuit 3 outputs the soft cut-off signal Soff when both the hard cut-off signal Hoff and the soft cut-off signal Soff are input. Therefore, when the detection of overcurrent by the overcurrent detection circuit 3 and the detection of short-circuit by the short-circuit detection circuit 6 occur simultaneously, soft cut-off of the switching element 1 is preferentially performed.

[0034] According to the switching element control device according to Embodiment 2, when an overcurrent less than three times the rated value flows through the switching element 1, hard cut-off of the switching element 1 is performed by the drive circuit 2, suppressing an increase in thermal stress and loss caused by the overcurrent. In addition, when a current greater than or equal to three times the rated value (an overcurrent caused by a short-circuit of the load) flows through the switching element 1, soft cut-off of the switching element 1 is performed by the soft cut-off circuit 9, suppressing the generation of an excessive surge voltage. In this way, an appropriate cut-off method corresponding to the magnitude of the overcurrent flowing through the switching element 1 is implemented, so that the reliability of the switching element 1 can be further improved compared with Embodiment 1.

[0035] The switching element control devices of Embodiments 1 and 2 can also output a fault signal FO indicating an abnormality to the system in which the switching element control device is incorporated when cutting off the switching element 1 to protect the switching element 1 from overcurrent damage. For example, in Embodiment 2, as shown in Figure 2 , it is configured to output the fault signal FO from the cut-off method selection circuit 8. The cut-off method selection circuit 8 may not output the fault signal FO when a hard cut-off signal Hoff is input from the overcurrent detection circuit 3 (that is, when an overcurrent less than three times the rated value is detected. Hereinafter referred to as "when an overcurrent is detected"), and output the fault signal FO only when a soft cut-off 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 a short circuit is detected"). In this 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.

[0036] Generally, in order to have a margin with respect to the maximum current during use considering the worst case, the switching element 1 is selected as a switching element having a rated value larger than the current during stable operation (that is, an over-specification switching element). As described above, when the system continues the normal operation when an overcurrent is detected, the current flowing through the switching element 1 is automatically suppressed to a set value. Therefore, as the switching element 1, a switching element having a rated value close to the current during stable operation can be used, resulting in a cost reduction.

[0037] In addition, when the switching element 1 is an IGBT, since the IGBT has a built-in voltage, the stable loss in the low-current region is large. Therefore, depending on the characteristics of the IGBT, stable operation continues even when an overcurrent near the rated value of the IGBT occurs, and thus a cost reduction can also be expected.

[0038] Furthermore, the respective embodiments can be freely combined, and the respective embodiments can be appropriately deformed and omitted.

[0039] <Appendix>

[0040] Hereinafter, the respective aspects of the present invention are collectively described in the appendix.

[0041] (Appendix 1)

[0042] A switching element control device, comprising:

[0043] A drive circuit that drives a switching element according to a drive control signal;

[0044] A first reference power supply that outputs a first reference voltage;

[0045] A reference voltage control unit that controls the first reference power supply according to a reference voltage setting signal, thereby adjusting the first reference voltage; and

[0046] An overcurrent detection circuit that outputs a first cut-off signal if the on-voltage of the switching element becomes greater than or equal to the first reference voltage,

[0047] The drive circuit performs a hard cut-off of the switching element according to the first cut-off signal.

[0048] (Appendix 2)

[0049] The switching element control device according to Appendix 1, wherein,

[0050] The switching element is made of silicon carbide.

[0051] (Appendix 3)

[0052] The switching element control device according to Appendix 1 or Appendix 2, wherein,

[0053] It further has:

[0054] A second reference power supply that outputs a second reference voltage;

[0055] A short-circuit detection circuit that outputs a second cut-off signal if the on-voltage of the switching element becomes greater than or equal to the second reference voltage;

[0056] A soft cut-off circuit that performs a soft cut-off of the switching element according to the second cut-off signal; and

[0057] A cut-off method selection circuit that receives the first cut-off signal and the second cut-off signal, and inputs the first cut-off signal to the drive circuit to perform the hard cut-off of the switching element when only the first cut-off signal is input, and inputs the second cut-off signal to the soft cut-off circuit to perform the soft cut-off of the switching element when only the second cut-off signal is input or both the first cut-off signal and the second cut-off signal are input.

[0058] (Appendix 4)

[0059] The switching element control device according to Appendix 3, wherein,

[0060] The first reference voltage is set to a value lower than the second reference voltage.

[0061] (Appendix 5)

[0062] The switching element control device according to Appendix 3 or Appendix 4, wherein,

[0063] When the second cut-off signal is output from the short-circuit detection circuit, a fault signal is output.

[0064] Description of reference numerals

[0065] 1 Semiconductor 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 Cut-off method selection circuit, 9 Soft cut-off circuit, Hoff Hard cut-off signal, Soff Soft cut-off signal, Vin Drive control signal, Vs Reference voltage setting signal, FO Fault signal.

Claims

1. A switching element control device, comprising: A driving circuit, which drives the switching element according to a driving control signal; a first reference power supply which outputs a first reference voltage; a reference voltage control unit that controls the first reference power supply according to a reference voltage setting signal to adjust the first reference voltage; as well as an overcurrent detection circuit which outputs a first cutoff signal if the on-voltage of the switch element becomes greater than or equal to the first reference voltage, The drive circuit performs hard-off of the switching element according to the first cutoff signal.

2. The switching element control device according to claim 1, wherein: The switching element is made of silicon carbide.

3. The switching element control device according to claim 1 or 2, wherein: Also features: a second reference power supply which outputs a second reference voltage; a short-circuit detection circuit which outputs a second cutoff signal if the on-voltage of the switch element becomes greater than or equal to the second reference voltage; a soft cut-off circuit for softly cutting off the switch element according to the second cut-off signal; as well as A cut-off method selection circuit receives the first cut-off signal and the second cut-off signal, and when only the first cut-off signal is input, inputs the first cut-off signal to the drive circuit to perform the hard cut-off of the switch element, and when only the second cut-off signal is input or both the first cut-off signal and the second cut-off signal are input, inputs the second cut-off signal to the soft cut-off circuit to perform the soft cut-off of the switch element.

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

5. The switching element control device according to claim 3 or 4, wherein: When the second cutoff signal is output from the short-circuit detection circuit, a fault signal is output.

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