JP2020136735A - Protection circuit - Google Patents

Abstract

To provide a technique capable of improving overcurrent detection accuracy by protecting a switch circuit from overcurrent and preventing erroneous detection of overcurrent.SOLUTION: A protection circuit 1 includes a voltage detection circuit 5, an overcurrent detection circuit 7, and a threshold value changing means. The protection circuit 1 detects an input voltage input to MOSFETs 3a and 3b. The overcurrent detection circuit 7 detects an overcurrent of the MOSFETs 3a and 3b on the basis of a Vds voltage applied to the MOSFETs 3a and 3b and a threshold voltage Vtg. The threshold value changing means changes the threshold voltage Vtg according to the input voltage input to the MOSFETs 3a and 3b detected by the voltage detection circuit 5.SELECTED DRAWING: Figure 1

Description

The present invention relates to a protection circuit.

The main circuit for driving a motor composed of a power MOSFET can control the rotation of the motor by supplying input power to the motor via a MOSFET (Metal Oxide Semiconductor Field Effect Transistor). As a method of detecting the overcurrent to the MOSFET, there is a method of using a low resistance and high rated current detection shunt resistor, but the drive current of the motor is on the order of several tens of A to several hundreds of A, and the size is required to meet the rating. It is less feasible because it requires the use of large resistors.

A configuration is known in which the current value flowing through the MOSFET is estimated by monitoring the voltage between the drain and the source of the MOSFET, and the overcurrent of the motor and the MOSFET is detected. As a related technique, for example, there is Patent Document 1.

Japanese Unexamined Patent Publication No. 2010-28961

However, the method of detecting the overcurrent of the MOSFET by the voltage between the drain and the source monitors a weak voltage (about 0 to 1 V), so that the variation of the MOSFET (individual difference) and the variation of the overcurrent detection circuit (individual difference) Will be greatly affected by. Further, since the on-resistance of the MOSFET has a positive temperature coefficient, the threshold value used for determining the overcurrent is set so that the overcurrent detection circuit reliably protects the MOSFET and prevents erroneous detection during normal operation. It is necessary to set it to an appropriate value each time. However, when the voltage threshold value is set large, it becomes difficult to reliably protect the MOSFET from overcurrent, and when the voltage threshold value is set small, there is a high possibility that erroneous detection will occur. Therefore, it has been desired to prevent erroneous detection and improve the detection accuracy of overcurrent while protecting the switch circuit such as MOSFET from overcurrent.

An object of one aspect of the present invention is to provide a technique capable of improving the detection accuracy of overcurrent by preventing erroneous detection of overcurrent while protecting the switch circuit from overcurrent.

The protection circuit according to one embodiment of the present invention detects an overcurrent of the switch circuit based on a voltage detection circuit that detects an input voltage input to the switch circuit and a voltage applied to the switch circuit and a threshold voltage. The overcurrent detection circuit and the threshold value changing means for changing the threshold voltage according to the input voltage input to the switch circuit detected by the voltage detection circuit are provided.

Therefore, even when the voltage applied to the switch circuit that changes based on the input voltage changes, the threshold voltage can be changed according to the input voltage. Therefore, since the overcurrent can be detected at the threshold voltage corresponding to the input voltage without setting the threshold voltage small, erroneous detection can be prevented. Further, since the overcurrent can be detected at the threshold voltage corresponding to the input voltage without setting a large threshold voltage, the switch circuit can be protected from the overcurrent. Thereby, the overcurrent detection accuracy can be improved.

Further, the threshold value changing means includes a threshold value changing circuit composed of a resistance element and a control circuit for controlling the threshold value changing circuit. The control circuit outputs a threshold control signal to the threshold change circuit according to an input voltage input to the switch circuit detected by the voltage detection circuit. The threshold value changing circuit changes the threshold voltage based on the threshold value control signal output from the control circuit.

Therefore, the threshold voltage can be changed from the control circuit side based on the threshold control signal output from the control circuit. As a result, the control of the threshold voltage can be centralized on the control circuit side.

Further, a temperature sensor for detecting the temperature state of the switch circuit is further provided. The threshold value changing means changes the threshold voltage according to the input voltage input to the switch circuit detected by the voltage detection circuit and the temperature of the switch circuit detected by the temperature sensor.

Therefore, in addition to the change in the voltage applied to the switch circuit that changes based on the input voltage, even if the temperature of the switch circuit changes, the threshold voltage can be changed according to the input voltage and the temperature of the switch circuit. it can. Therefore, the overcurrent can be detected at the threshold voltage corresponding to the input voltage and the temperature without setting the threshold voltage small, so that erroneous detection can be prevented. Further, since the overcurrent can be detected at the threshold voltage corresponding to the input voltage and the temperature without setting a large threshold voltage, the switch circuit can be protected from the overcurrent. Thereby, the overcurrent detection accuracy can be improved.

According to the present invention, it is possible to improve the overcurrent detection accuracy by preventing erroneous detection of overcurrent while protecting the switch circuit from overcurrent.

It is a figure which shows an example of the protection circuit of this embodiment.

The present embodiment will be described in detail below with reference to the drawings.
A method of protecting the protection circuit according to the present embodiment of the present invention will be described. FIG. 1 is a diagram showing an example of a protection circuit of the present embodiment. The protection circuit 1 shown in FIG. 1 includes a DC power supply 2, a MOSFET (switch circuit) 3a, 3b, a temperature sensor 4, a voltage detection circuit 5, a comparator 6a, 6b, an overcurrent detection circuit 7, an AND circuit 8a, 8b, and a threshold change. It has a circuit 9, voltage dividing circuits 10a and 10b, and a control circuit 12. The voltage dividing circuit 10a has resistance elements 11a and 11b. The voltage dividing circuit 10b has resistance elements 11c and 11d. In this embodiment, a MOSFET is used as the switch circuit, but a switch circuit other than the MOSFET may be used.

The voltage detection circuit 5 has resistance elements 11e and 11f. The threshold value changing circuit 9 has resistance elements 11g and 11h. The control circuit 12 includes a temperature detection unit 13, a voltage detection unit 14, MOSFET control units 15a and 15b, a short circuit detection unit 16a and 16b, and a threshold value control unit 17.

The protection circuit 1 has a three-phase output inverter circuit. MOSFETs 3a and 3b are connected to the DC power supply 2 to form one inverter circuit. The three-phase output inverter circuit has two more MOSFET groups similar to the MOSFETs 3a and 3b, but description and illustration thereof will be omitted. The motor 20 is connected to the midpoint of the MOSFETs 3a and 3b. Although not shown, the midpoints of two groups of MOSFET sets similar to MOSFETs 3a and 3b are connected to the motor 20, respectively. The control circuit 12 is composed of, for example, a microcomputer, and drives each gate so as to turn on and off each of the MOSFETs 3a and 3b.

The temperature sensor 4 is arranged in the vicinity of the MOSFETs 3a and 3b, and can measure the temperature of the MOSFETs 3a and 3b. The temperature sensor 4 may not only directly measure the temperature of the MOSFETs 3a and 3b, but also measure the temperature of the MOSFETs 3a and 3b by estimating the temperature of the MOSFETs 3a and 3b based on the temperature in the vicinity of the MOSFETs 3a and 3b. The temperature sensor 4 is connected to the control circuit 12. The temperature sensor 4 can be used by applying the thermistor used for temperature protection of the MOSFETs 3a and 3b in the protection circuit 1. As a result, an increase in component cost can be suppressed.

The temperature sensor 4 outputs the measured temperature information to the control circuit 12. The temperature detection unit 13 of the control circuit 12 detects the temperature information of the MOSFETs 3a and 3b output from the temperature sensor 4. The temperature detection unit 13 outputs the detected temperature information to the threshold value control unit 17.

The voltage detection circuit 5 is connected to the MOSFETs 3a and 3b, and can detect the input voltage input to the MOSFETs 3a and 3b. Specifically, in the voltage detection circuit 5, one end of the resistance element 11e is connected to the DC power supply 2. One end of the resistance element 11f is connected to the GND. The other ends of the resistance element 11e and the resistance element 11f are connected to the control circuit 12. The voltage detection circuit 5 detects the voltage Vg1 in which the input voltage Vin input from the DC power supply 2 is divided by the resistance elements 11e and 11f. The voltage detection circuit 5 can be used by applying the voltage detection circuit used for battery voltage monitoring (not shown) in the protection circuit 1. As a result, an increase in component cost can be suppressed.

The voltage detection circuit 5 outputs the detected voltage information to the control circuit 12. The voltage detection unit 14 of the control circuit 12 detects the voltage information output from the voltage detection circuit 5. The voltage detection unit 14 outputs the detected voltage information to the threshold value control unit 17.

Both MOSFETs 3a and 3b are n-channel MOSFETs. Comparators 6a and 6b are arranged in front of the overcurrent detection circuit 7.

The MOSFET 3a connects the drain to the non-inverting input terminal (+) of the comparator 6a via the voltage divider circuit 10a, and connects the source to the inverting input terminal (−) of the comparator 6a via the voltage divider circuit 10b. Further, a DC power supply 2 is connected to the drain of the MOSFET 3a.

The MOSFET 3b connects the drain to the non-inverting input terminal (+) of the comparator 6b via the voltage divider circuit 10b, and connects the source to the GND. A motor 20 is connected to the midpoint between the source of the MOSFET 3a and the drain of the MOSFET 3b.

The voltage dividing circuit 10a has a resistance element 11a and a resistance element 11b connected in series with each other, and is provided between the drain of the MOSFET 3a and the GND. The connection points of the resistance element 11a and the resistance element 11b are connected to the non-inverting input terminal (+) of the comparator 6a. Therefore, the drain voltage V1 of the MOSFET 3a and the voltage Vd1 divided by the resistance element 11a and the resistance element 11b are supplied to the non-inverting input terminal (+) of the comparator 6a.

The voltage dividing circuit 10b has a resistance element 11c and a resistance element 11d connected in series with each other, and is provided between the source of the MOSFET 3a and the drain of the MOSFET 3b and the GND connected via the threshold value changing circuit 9. ing. The connection points of the resistance element 11c and the resistance element 11d are connected to the inverting input terminal (−) of the comparator 6a and the non-inverting input terminal (+) of the comparator 6b. Therefore, the source voltage V2 of the MOSFET 3a is divided by the resistance element 11c and the resistance element 11d, and the voltage Vd2 is supplied to the inverting input terminal (−) of the comparator 6a. Further, the drain voltage V3 of the MOSFET 3b is divided by the resistance element 11c and the resistance element 11d, and the voltage Vd3 is supplied to the non-inverting input terminal (+) of the comparator 6b.

The comparator 6a connects the drain (voltage Vd1) of the MOSFET 3a to the non-inverting input terminal (+) via the voltage divider circuit 10a, and connects the drain (voltage Vd1) of the MOSFET 3a to the inverting input terminal (-) via the voltage divider circuit 10b to the source (voltage Vd2) of the MOSFET 3a. ) Is connected.

The comparator 6b connects the drain (voltage Vd3) of the MOSFET 3b to the non-inverting input terminal (+) via the voltage divider circuit 10b, and connects the GND (reference voltage GND) to the inverting input terminal (−).

The Vds voltage of the MOSFETs 3a and 3b changes according to the flowing current. Therefore, a threshold value changing circuit 9 for changing the threshold voltage Vtg is connected to the input terminals of the comparators 6a and 6b. Specifically, the comparator 6a connects the threshold value changing circuit 9 to the inverting input terminal (−) via the voltage dividing circuit 10b. Further, the comparator 6b connects the threshold value changing circuit 9 to the non-inverting input terminal (+) via the voltage dividing circuit 10b.

The threshold value change circuit 9 is connected to the threshold value control unit 17 of the control circuit 12. As a result, the threshold voltage Vtg can be controlled on the control circuit 12 side. The threshold value changing circuit 9 changes the threshold voltage Vtg based on the threshold value control signal Vts (predetermined voltage) output from the threshold value control unit 17 of the control circuit 12. Specifically, the threshold value changing circuit 9 divides the threshold value control signal Vts output from the threshold value control unit 17 according to the voltage division ratio set by the resistance element 11g and the resistance element 11h to obtain the threshold value control voltage Vtt. Generate. The threshold value change circuit 9 changes the threshold value control voltage Vtt based on the threshold value control signal Vts output from the threshold value control unit 17. The threshold voltage Vtg is a voltage that changes in proportion to the threshold control voltage Vtt changed by the threshold change circuit 9. The resistance value of the resistance element 11h arranged on the GND side is set to be larger than the resistance value of the resistance element 11g arranged on the threshold control unit 17 side.

The threshold control unit 17 outputs the threshold control signal Vts to the threshold change circuit 9 according to the input voltage Vg1 detected by the voltage detection circuit 5 and input to the MOSFETs 3a and 3b detected by the voltage detection circuit 14. Specifically, the threshold control unit 17 outputs a high-level threshold control signal Vts as the voltage detected by the voltage detection unit 14 increases. Further, the threshold control unit 17 outputs a low level threshold control signal Vts as the voltage detected by the voltage detection unit 14 decreases.

A table, a relational expression, a map, or the like showing the relationship between the voltage detected by the voltage detection unit 14 and the level of the threshold control signal Vts is stored in advance in a memory or a register (not shown). The threshold control unit 17 can output an appropriate threshold control signal Vts according to the voltage detected by the voltage detection unit 14 by referring to a table, a relational expression, a map, or the like stored in a memory or a register. ..

The threshold value change circuit 9 changes the threshold value control voltage Vtt based on the threshold value control signal Vts output according to the input voltage Vg1 input to the MOSFETs 3a and 3b detected by the voltage detection circuit 5.

The threshold value changing means of the present invention includes, for example, a threshold value changing circuit 9 composed of resistance elements 11g and 11h, and a threshold value control unit 17 for controlling the threshold value changing circuit 9. The threshold value changing means changes the threshold voltage Vtg according to the input voltage Vg1 input to the MOSFETs 3a and 3b detected by the voltage detection circuit 5.

The threshold value changing means changes the threshold voltage Vtg according to the input voltage Vg1 input to the MOSFETs 3a and 3b detected by the voltage detection circuit 5 and the temperature of the MOSFETs 3a and 3b detected by the temperature sensor 4. May be good.

In this case, the threshold control unit 17 includes the input voltage Vg1 detected by the voltage detection circuit 5 and input to the MOSFETs 3a and 3b detected by the voltage detection unit 14, and the temperatures of the MOSFETs 3a and 3b detected by the temperature sensor 4. , The threshold control signal Vts is output to the threshold change circuit 9. Specifically, the threshold control unit 17 has a high level threshold control signal as the temperature detected by the temperature detection unit 13 increases, in addition to the control based on the voltage level detected by the voltage detection unit 14. Output Vts. Further, the threshold control unit 17 outputs a low level threshold control signal Vts as the temperature detected by the temperature detection unit 13 decreases.

In this case, a memory or register (not shown) such as a table, a relational expression, or a map showing the relationship between the voltage detected by the voltage detection unit 14, the temperature detected by the temperature detection unit 13, and the level of the threshold control signal Vts is not shown. It is stored in advance in. The threshold control unit 17 refers to a table, a relational expression, a map, or the like stored in a memory or a register, and is appropriate according to the voltage detected by the voltage detection unit 14 and the temperature detected by the temperature detection unit 13. The threshold control signal Vts can be output.

Here, the source voltage Vd2 of the MOSFET 3a supplied to the inverting input terminal (−) of the comparator 6a increases by the threshold voltage Vtg in proportion to the threshold control voltage Vtt changed by the threshold change circuit 9. Similarly, the drain voltage Vd3 of the MOSFET 3b supplied to the non-inverting input terminal (+) of the comparator 6b increases by the threshold voltage Vtg in proportion to the threshold control voltage Vtt changed by the threshold change circuit 9.

Therefore, the voltage input to the inverting input terminal (−) of the comparator 6a is the source voltage Vd2 of the MOSFET 3a + the threshold voltage Vtg. Similarly, the voltage input to the non-inverting input terminal (+) of the comparator 6b is “drain voltage Vd3 of MOSFET 3b + threshold voltage Vtg”.

When the Vds voltage between the drain and source of the MOSFET 3a is equal to or less than the threshold voltage Vtg (that is, when “Vd1 ≦ Vd2 + Vtg”), the comparator 6a outputs the output signal of “Low” to the overcurrent detection circuit 7.

When the Vds voltage between the drain and source of the MOSFET 3a increases and this Vds voltage exceeds the threshold voltage Vtg (that is, “Vd1> Vd2 + Vtg”), the output signal of the comparator 6a is inverted from “Low” to “Hi”. To do. As a result, the comparator 6a can monitor the Vds voltage of the MOSFET 3a.

Further, when the Vds voltage between the drain and the source of the MOSFET 3b is equal to or less than the threshold voltage Vtg (that is, when “Vd3 + Vtg ≦ reference voltage GND”), the comparator 6b outputs the output signal of “Low” to the overcurrent detection circuit 7. ..

When the Vds voltage between the drain and source of the MOSFET 3b increases and this Vds voltage exceeds the threshold voltage Vtg (that is, “Vd3 + Vtg> reference voltage GND”), the output signal of the comparator 6b changes from “Low” to “Hi”. Invert to. As a result, the comparator 6b can monitor the Vds voltage of the MOSFET 3b.

The overcurrent detection circuit 7 can detect whether or not an overcurrent is generated in the MOSFETs 3a and 3b based on the output signals output from the comparators 6a and 6b. The overcurrent detection circuit 7 may detect whether or not an overcurrent has occurred based on the logical sum of the output signals of the comparators 6a and 6b.

Therefore, the overcurrent detection circuit 7 can detect the overcurrent of the MOSFETs 3a and 3b from the output signals output by the comparators 6a and 6b based on the Vds voltage between the drain and the source of the MOSFETs 3a and 3b and the threshold voltage Vtg. it can.

The MOSFET control units 15a and 15b turn on and off each of the MOSFETs 3a and 3b by outputting a sinusoidal gate signal (PWM (Pulse Width Modulation) signal) to the MOSFETs 3a and 3b to control the drive of the MOSFETs 3a and 3b. .. The gate signal output from the MOSFET control unit 15a is a “Hi” signal. The MOSFETs 3a and 3b are controlled by gate signals output from the MOSFET control units 15a and 15b, respectively.

The overcurrent detection circuit 7 ANDs the overcurrent control signal of "Hi" when the overcurrent is not detected, that is, when the output signals output from the comparators 6a and 6b are "Low". Output to 8a and 8b. When the overcurrent detection circuit 7 detects an overcurrent, that is, when the output signals output from the comparators 6a and 6b are “Hi”, the overcurrent control signal of “Low” is transmitted to the AND circuit 8a, respectively. Output to 8b.

The short-circuit detection units 16a and 16b output the short-circuit control signal of "Hi" to the AND circuits 8a and 8b, respectively, when the short-circuit is not detected, and when the short-circuit is detected, the short-circuit control of "Low" is performed. The signal is output to the AND circuits 8a and 8b, respectively.

A gate signal output from the MOSFET control units 15a and 15b and an overcurrent control signal output from the overcurrent detection circuit 7 are supplied to one of the input terminals of the AND circuits 8a and 8b, respectively. Short-circuit control signals output from the short-circuit detection units 16a and 16b are supplied to the other input terminals of the AND circuits 8a and 8b, respectively. The output terminals of the AND circuits 8a and 8b are connected to the gates of the MOSFETs 3a and 3b, respectively.

The behavior of the AND circuits 8a and 8b when a short circuit is not detected will be described. When a short circuit is not detected, the short circuit control signal of "Hi" supplied from the short circuit detection units 16a and 16b is input to the other input terminals of the AND circuits 8a and 8b, respectively. When the overcurrent is not detected, the overcurrent control signal of "Hi" supplied from the overcurrent detection circuit 7 and the MOSFET control units 15a and 15b are connected to one of the input terminals of the AND circuits 8a and 8b. The gate signal of "Hi" supplied from is input respectively. Therefore, the “Hi” gate signal is output from the output terminals of the AND circuits 8a and 8b.

On the other hand, when an overcurrent is detected, the “Low” overcurrent control signal and the MOSFET control units 15a and 15b supplied from the overcurrent detection circuit 7 are connected to one of the input terminals of the AND circuits 8a and 8b. The gate signal of "Hi" supplied from is input respectively. Therefore, in the overcurrent detection circuit 7, the gate signal output from the output terminals of the AND circuits 8a and 8b becomes “Low”, and the MOSFETs 3a and 3b can be forcibly stopped.

The overcurrent detection circuit 7 is synchronized with the switching of the MOSFETs 3a and 3b, and when a gate signal is input to the MOSFETs 3a and 3b, the overcurrent detection function becomes effective. That is, the overcurrent detection circuit 7 is effective only when the MOSFETs 3a and 3b are turned on.

Then, when an overcurrent flows through the MOSFETs 3a and 3b, the overcurrent detection circuit 7 outputs a “Low” overcurrent control signal to the AND circuits 8a and 8b, respectively, to output the gate signal of the MOSFETs 3a and 3b. Forcibly stop. The AND circuits 8a and 8b do not output a gate signal when a "Low" signal is input from either of the two input terminals, so that the MOSFETs 3a and 3b are forcibly stopped, respectively. As a result, the overcurrent detection circuit 7 can limit the current flowing through the MOSFETs 3a and 3b.

When no short circuit is detected, the short circuit control signals output from the short circuit detection units 16a and 16b are "Hi", and the gate signals output from the MOSFET control units 15a and 15b are "Hi" signals. Is. Therefore, the “Hi” gate signal is output from the output terminals of the AND circuits 8a and 8b, respectively.

When a short circuit is detected, the short circuit control signal output from the short circuit detection units 16a and 16b is "Low", and the gate signal output from the MOSFET control units 15a and 15b is a "Hi" signal. Therefore, the short-circuit detection units 16a and 16b can forcibly stop the MOSFETs 3a and 3b by setting the gate signal output from the output terminals of the AND circuits 8a and 8b to "Low".

The threshold value changing means of the protection circuit 1 of the above-described embodiment changes the threshold voltage Vtg according to the input voltage input to the MOSFETs 3a and 3b detected by the voltage detection circuit 5. Therefore, even when the Vds voltage applied to the MOSFETs 3a and 3b that changes based on the input voltage changes, the threshold voltage Vtg can be changed according to the input voltage. Therefore, since the overcurrent can be detected at the threshold voltage Vtg corresponding to the input voltage without setting the threshold voltage Vtg small, erroneous detection can be prevented. Further, since the overcurrent can be detected at the threshold voltage Vtg corresponding to the input voltage without setting the threshold voltage Vtg large, the MOSFETs 3a and 3b can be protected from the overcurrent. Thereby, the overcurrent detection accuracy can be improved.

Further, the threshold value changing means of the protection circuit 1 of the above-described embodiment includes a threshold value changing circuit 9 composed of resistance elements 11g and 11h, and a control circuit 12 for controlling the threshold value changing circuit 9. The control circuit 12 outputs a threshold control signal to the threshold change circuit 9 according to the input voltage input to the MOSFETs 3a and 3b detected by the voltage detection circuit 5. The threshold value changing circuit 9 changes the threshold voltage Vtg based on the threshold value control signal output from the control circuit 12. Therefore, the threshold voltage Vtg can be changed from the control circuit 12 side based on the threshold control signal output from the control circuit 12. As a result, the control of the threshold voltage Vtg can be integrated on the control circuit 12 side.

Further, the protection circuit 1 of the above-described embodiment further includes a temperature sensor 4 for detecting the temperature state of the MOSFETs 3a and 3b. The threshold value changing means changes the threshold voltage Vtg according to the input voltage input to the MOSFETs 3a and 3b detected by the voltage detection circuit 5 and the temperature of the MOSFETs 3a and 3b detected by the temperature sensor 4.

Therefore, even if the temperature of the MOSFETs 3a and 3b changes in addition to the change of the Vds voltage applied to the MOSFETs 3a and 3b that changes based on the input voltage, the threshold voltage Vtg is changed according to the input voltage and the temperature of the MOSFETs 3a and 3b. Can be changed. Therefore, since the overcurrent can be detected at the threshold voltage Vtg corresponding to the input voltage and the temperature without setting the threshold voltage Vtg small, erroneous detection can be prevented. Further, since the overcurrent can be detected at the threshold voltage Vtg corresponding to the input voltage and the temperature without setting the threshold voltage Vtg large, the MOSFETs 3a and 3b can be protected from the overcurrent. Thereby, the overcurrent detection accuracy can be improved.

The present invention is not limited to the above embodiments, and various improvements and changes can be made without departing from the gist of the present invention.

1 Protection circuit 2 DC power supply 4 Temperature sensor 5 Voltage detection circuit 6a, 6b Comparator 7 Overcurrent detection circuit 8a, 8b AND circuit 9 Threshold change circuit 10a, 10b Voltage divider circuit 11a to 11h Resistance element 12 Control circuit 13 Temperature detection unit 14 Voltage detection unit 15a, 15b MOSFET control unit 16a, 16b Short circuit detection unit 17 Threshold control unit 20 Motor

Claims (3)

A voltage detection circuit that detects the input voltage input to the switch circuit, and
An overcurrent detection circuit that detects an overcurrent in the switch circuit based on the voltage applied to the switch circuit and the threshold voltage, and an overcurrent detection circuit.
A threshold value changing means for changing the threshold voltage according to an input voltage input to the switch circuit detected by the voltage detection circuit, and
A protection circuit characterized by being provided with. The protection circuit according to claim 1.
The threshold value changing means is configured to include a threshold value changing circuit composed of a resistance element and a control circuit for controlling the threshold value changing circuit.
The control circuit outputs a threshold control signal to the threshold change circuit according to the input voltage input to the switch circuit detected by the voltage detection circuit.
The threshold value changing circuit is a protection circuit characterized in that the threshold voltage is changed based on the threshold value control signal output from the control circuit. The protection circuit according to claim 1 or 2.
A temperature sensor for detecting the temperature state of the switch circuit is further provided.
The threshold value changing means changes the threshold voltage according to the input voltage input to the switch circuit detected by the voltage detection circuit and the temperature of the switch circuit detected by the temperature sensor. Protection circuit.

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