JP3231450B2 - Semiconductor element protection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protection circuit for protecting a semiconductor element used in a power converter or the like from overcurrent.

[0002]

2. Description of the Related Art FIG. 5 shows a prior art of this kind of protection circuit. In the figure, 1 is a semiconductor element for switching operation, 2 is a current detector for detecting a current flowing through the semiconductor element 1, 3 is a protection level setting unit, 4 is a protection level of a current detection value of the current detector 2 by the setting unit 3. The comparator 5, which outputs a detection signal when the detection signal reaches the threshold value, is a drive circuit of the semiconductor element 1 to which the detection signal is input.

The operation will be described. When the detected current value increases and reaches a protection level as shown in FIG. 6A, a detection signal is output from the comparator 4 and the driving circuit 5 controls the semiconductor device 1 to operate. Turn off instantly. This off period is continued until the end of the switching period.

[0004]

In the above prior art, the semiconductor element 1 can be protected for a short time, but such a protection state continues for a long time, during which the semiconductor element 1 is switched many times. Then, the protection of the semiconductor element 1 becomes impossible due to the heat generated by the switching. For this reason, conventionally, although the semiconductor element 1 has the ability to be used up to the point A in the safe operation area (SOA) of FIG.
Since the device is used at point ´, there has been a problem that the capability of the element cannot be fully utilized.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. The object of the present invention is to enable not only overcurrent protection but also thermal protection so that the performance of the device can be fully exhibited. An object of the present invention is to provide a protection circuit for a semiconductor device.

[0006]

In order to achieve the above object, the present invention provides a comparator for outputting a detection signal when a current of a semiconductor element performing a switching operation reaches a protection level, and a semiconductor based on the detection signal. In a protection circuit for a semiconductor device including a drive circuit for turning off the device, when the detection signal is output for a set number of times within a predetermined time,
Said control signal to continuously clear the semiconductor device in which with a drive stop control circuit for outputting to the driving circuit.

The drive stop control circuit includes a counter for counting the detection signal of the comparator, a flip-flop for holding the count-up signal of the counter for a certain period of time, and a count-up signal output from the start of counting of the counter. It is preferable that an oscillator that resets at a cycle longer than the time required to generate the control signal for the drive circuit be generated based on the output signal of the flip-flop.

[0008]

According to the present invention, when the number of times that the current flowing through the semiconductor element reaches the protection level exceeds the number of times set by the drive stop control circuit, the control circuit outputs a control signal to the drive circuit, and the drive circuit The device is continuously turned off. If the set number of times is determined in consideration of the rating of the element and the like, heat generation of the semiconductor element due to switching can be prevented, and thermal protection of the element can be achieved.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of this embodiment. The same components as those in FIG. 5 are denoted by the same reference numerals, detailed description thereof will be omitted, and different portions will be mainly described below. That is, in this embodiment, the detection signal from the comparator 4 is input to the drive stop control circuit 6, and the control signal output from the drive stop control circuit 6 is input to the drive circuit 5.

The drive stop control circuit 6 outputs a control signal to the drive circuit 5 when the detection signal from the comparator 4 is output more than a set number of times within a predetermined time T, and stops the operation of the drive circuit 5. It is configured as follows. The predetermined time T and the set number of times are appropriately set according to the rating of the semiconductor element 1 to be protected.

Next, the schematic operation of this embodiment will be described with reference to FIG. As shown in FIG.
When the current reaches the protection level, the drive circuit 5 turns off the semiconductor element 1 by the detection signal from the comparator 4. Since the detection signal is also input to the drive stop control circuit 6, when the detection signal is input more than a set number of times, a control signal is output from the drive stop control circuit 6 to stop the operation of the drive circuit 5. Thereby, the switching operation of the semiconductor element 1 is stopped thereafter, and the operation of the power converter is stopped.

FIG. 3 is a detailed block diagram of the above embodiment. In the figure, a current detector 2 is connected to an inverting input terminal of a comparator 4, and a protection level setting device 3 is connected to a non-inverting input terminal. The drive stop control circuit 6 includes a comparator 4
Counter 6 to which the detection signal from is input as a clock
2, an oscillator 61 for inputting a reset signal to the counter 62, and a flip-flop 63 for inputting a count-up signal of the counter 62.

The drive circuit 5 includes an AND circuit 51 to which a drive signal from a signal generation circuit (not shown), a detection signal from the comparator 4 and an inverted output signal of the flip-flop 63 are input. I have. And AND circuit 5
1 is applied to the semiconductor element 1.

This operation will be described with reference to FIG.
First, each time the current flowing through the semiconductor element 1 reaches the protection level, a detection signal is output from the comparator 4, and this signal is counted by the counter 62. The counter 62 is configured to count up when the count value exceeds n within a predetermined time T, and the count value n is set in consideration of a limit value of thermal protection of the semiconductor element 1. The counter 62 is reset by a signal output from the oscillator 61 at a period longer than the predetermined time T.

As shown in FIG. 4, when the number of times that the current flowing through the semiconductor element 1 reaches the protection level is relatively small and the count value n 'does not reach n (n'<n), the counter 62 counts up. Without the counter 62, the oscillator 61
Is reset at a constant period by the output signal of During this time, the output signal of the flip-flop 63 is at the “High” level, and the output signal of the comparator 4 is at the “High” level when the current flowing through the semiconductor element 1 is smaller than the protection level, and is at the “Low” level when the current is larger than the protection level. A drive signal is output from the AND circuit 51 at an on / off timing equal to the current in FIG.

When the number of times that the current flowing through the semiconductor element 1 reaches the protection level increases, for example, when the count value exceeds n at time Ta (<T), the counter 62 counts up, and the flip-flop 63 outputs the count-up signal. Hold. As a result, the output signal of the flip-flop 63 is inverted and a signal of the “Low” level is input to the AND circuit 51, so that no drive signal is output and the power converter stops its operation.

The semiconductor device to which the present invention is applied is:
A thyristor other than the illustrated transistor may be used.

[0018]

As described above, according to the present invention, when the detection signal indicating that the current flowing through the semiconductor device has reached the protection level has exceeded the set number of times within a predetermined time, the device is continuously stopped. In addition, it is not necessary to consider the use of the device by partially wasting the capability of the device as in the related art, and it is possible to protect not only the overcurrent of the semiconductor device but also the heat generated by switching. Therefore, it is possible to reduce the element rating, reduce the size and weight of the power converter and the like, and reduce the cost.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is an operation explanatory diagram of the embodiment.

FIG. 3 is a circuit block diagram showing a detailed configuration of the embodiment.

FIG. 4 is an operation explanatory diagram of FIG. 3;

FIG. 5 is a circuit block diagram showing a conventional technique.

FIG. 6 is an operation explanatory diagram of a conventional technique.

FIG. 7 is an explanatory diagram of a safe operation area of the semiconductor element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor element 2 Current detector 3 Protection level setter 4 Comparator 5 Drive circuit 6 Drive stop control circuit 51 AND circuit 61 Oscillator 62 Counter 63 Flip-flop

Claims (2)

(57) [Claims] A comparator for outputting a detection signal when a current of a semiconductor element performing a switching operation reaches a protection level;
In the protection circuit for a semiconductor device and a driving circuit for turning off the semiconductor device based on the detection signal, when said detection signal is output set number of times or more within a predetermined time, continuously controlled for turning off the semiconductor element A protection circuit for a semiconductor element, comprising a drive stop control circuit for outputting a signal to a drive circuit. 2. A drive stop control circuit comprising: a counter for counting a detection signal of a comparator; a flip-flop for holding a count-up signal of the counter for a certain period of time; and a count-up signal output from the counter when counting is started. 2. The protection circuit for a semiconductor device according to claim 1, further comprising: an oscillator resetting at a cycle longer than a time period until the control signal for the drive circuit is generated based on an output signal of the flip-flop.