JPS63268432A - Short-circuit protective circuit - Google Patents

Abstract

PURPOSE:To reduce a whole circuit by detecting an overcurrent without using a current transformer or a current shunt. CONSTITUTION:A switching element 1 for supplying a current to a load is controlled by a driver 2. When an overcurrent flows to the element 1, a high side voltage of the element 1 is abnormally raised. This voltage is applied to a voltage detector 3, and a voltage is generated across a resistor 7 by the current. This voltage is compared by a voltage comparator 4 with the voltage of a reference voltage source 5. If it exceeds it, the comparator 4 feeds a signal to a driver controller 6 to turn it ON, thereby reducing the high side voltage of a resistor 13 to turn OFF a driving transistor 12. Thus, the driving signal of the switching element is interrupted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a protection circuit for an industrial device such as an inverter using a power switching device when a special overcurrent flows due to a load short circuit of the device.

[Conventional technology]

FIG. 2 is a circuit diagram showing a short-circuit protection circuit for an inverter using, for example, a conventional power switch element.
is a switch element, and 2 is a drive circuit. Also 8, 9
are current transformers for detecting load current, and these are not used simultaneously on one circuit, but one of them is used. Reference numeral 10 denotes a short circuit detection circuit that detects short circuits in the main circuit using signals from the current transformer 8 and the shunt 9.

Next, the operation will be explained. As shown in FIG. 2, in this conventional example, an overcurrent when a load short circuit occurs in the main circuit is detected by a current transformer 8 or a current shunt 9.

The current transformer 8 or the current shunt 9 constantly detects the amount of current flowing through the main circuit, and outputs this detected value to the short circuit detection circuit 10. When the short circuit detection circuit 10 determines that the detected value is an overcurrent, it sends a signal to the drive circuit 2 that drives the switch element 1 to stop the operation of the circuit. As a result, the switch element 1 is turned off, and destruction of the element due to passage of overcurrent can be prevented.

[Problem that the invention seeks to solve]

Conventional short-circuit protection circuits are configured as described above, and because they use current shunts and current transformers to detect overcurrent, the entire circuit becomes large.Also, when current shunts are used, current always flows, so a large amount of power is required at all times. Loss (I”R
), so there were problems such as the need to pay attention to heat dissipation.

The present invention has been made to solve the above-mentioned problems, and aims to provide a short-circuit protection circuit that does not require consideration of heat radiation and allows the entire circuit to be miniaturized.

[Means for solving problems]

A short-circuit protection circuit according to the present invention protects against a load short-circuit of a load driven by a power switching element in a circuit configured with a power switching element.

In a short-circuit protection circuit for detecting an inter-element short circuit between the power switching elements or an intra-element short circuit of the power switching element and shutting off the power switching element, a voltage for detecting the high side voltage of the power switching element. a detection means, a voltage comparator that compares the voltage detected by the voltage detection means with a reference voltage to detect any of the short circuits; and drive circuit control means for stopping the operation of the drive circuit of the switching element.

[Effect]

In this invention, the voltage detecting means detects the high side voltage of the power switching element, the voltage comparator detects a short circuit by comparing the voltage detected by the voltage detecting means with a reference voltage, and the voltage comparator A drive circuit control means that stops the operation of the drive circuit of the power switching element when a short circuit force is applied, and detects an abnormality in the voltage on the high side of the ψ switching element at the time of a short circuit and drives the switching element. Since the circuit is configured to break off, there is no need for a current transformer or current shunt, and the entire circuit can be made smaller.

Furthermore, by converting the entire circuit into a power IC, it becomes possible to incorporate it into a switching element or a drive circuit.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to the drawings. 1st
The figure is a circuit diagram showing a short-circuit protection circuit according to an embodiment of the present invention. In the figure, 1 is a switching element, 2 is a drive circuit for the switching element, and 3 is a voltage detector for detecting the voltage applied to the switching element. It is an element for
Consists of MOS FET or bipolar transistor. 4 is a voltage comparator for comparing whether or not the voltage detected by the voltage detection element 3 is normal; 5 is a reference voltage source for determining the normal voltage. Reference numeral 6 denotes a drive circuit control element for stopping the operation of the drive circuit 2 when an abnormality is detected by the voltage comparator 4, and is composed of a MOSFET.

7 is a resistor for converting the current from the voltage detection element 3 into a voltage for comparison with the reference voltage source 5 in the voltage comparator 4, and 11.13 is a resistor for supplying the base current to the drive transistor 12. It is.

Next, the operation will be explained. When a load short circuit or the like occurs in the main circuit and an overcurrent flows through the switching element 1, the voltage on the high side of the switching element 1 also increases abnormally compared to the case of normal operation.

When this voltage is applied to the voltage detection element 3 and a current flows, a voltage is generated across the resistor 7.

In normal operation, the voltage across the resistor 7 and the voltage of the reference voltage source 5 are the same, so the voltage comparator 4 does not operate and therefore does not supply a signal to the drive circuit control element 6, but the switching element 1 is supplied with the signal as described above. If an abnormality occurs, resistor 7
Since the voltage across the voltage exceeds the voltage of the reference voltage source 5, the voltage comparator 4 operates and supplies a signal to the drive circuit control element 6.

The drive circuit control element 6 that receives the signal from the voltage comparator 4 is immediately turned on. Then, since the potential on the high side of the resistor 13 decreases, the drive transistor 12 of the drive circuit 2 is turned off, and the drive signal of the switching element 1 is cut off.

As described above, in this embodiment, the voltage on the high side of the switching element is detected using a voltage detection element and a resistor, and the detected voltage is compared with a reference voltage using a voltage comparator. In some cases, the voltage comparator outputs a signal to the drive circuit control element, and the drive circuit control element that receives the signal operates to cut off the drive signal to the switching element of the drive circuit. Since the detection part is also made of semiconductor, there is no need to pay attention to heat radiation as when using a current shunt, and a highly reliable product can be obtained.
This has the effect of making the entire circuit smaller.

In addition, the circuit of this embodiment has all the circuit components made of semiconductor elements as described above, so its operating speed is extremely high compared to conventional circuits using current transformers or current shunts, and the protection performance is improved. It has the effect of getting expensive things.

Note that the short circuit protection circuit according to the present invention
It is also possible to convert it into C and incorporate it into switching elements and drive circuits, expanding the range of applications.

〔Effect of the invention〕

As described above, according to the present invention, in a circuit constituted by power switching elements, a load short-circuit of a load driven by the power switching element and an inter-element short-circuit between the power switching elements can be avoided.

Alternatively, in a short-circuit protection circuit for detecting an internal short circuit of the power switching element and interrupting the power switching element, a voltage detection means for detecting a high-side voltage of the power switching element; a voltage comparator that detects a short circuit in any of the above by comparing the detected voltage with a reference voltage; It is equipped with a drive circuit control means to stop the drive, and the abnormality detection section is also made of semiconductor.
There is no need for a current transformer or current shunt, and the device can be made smaller. Furthermore, since the process from detection to shutoff can be completed in a much shorter time than when using a conventional current transformer or current shunt, it has the effect of providing high protection performance.

Furthermore, if the entire circuit is made into a power IC, it can be built into a switching element or a drive circuit, and the range of applications can be expanded.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a short circuit protection circuit according to an embodiment of the present invention, and FIG. 2 is a block diagram showing a conventional short circuit protection circuit. 1 is a power switching element, 2 is a drive circuit, 3 is M
OS FET or bipolar transistor, 4 is a voltage comparator, 5 is a reference voltage source, 6 is a MOSFET, 7 is a resistor, 8 is a current transformer, 9 is a current shunt, 10 is an overcurrent detection circuit of the main circuit.

Claims (3)

[Claims] (1) A load short-circuit of a load driven by the power switching element in a circuit constituted by the power switching element, an inter-element short-circuit between the power switching elements,
Alternatively, in a short circuit protection circuit for detecting an internal short circuit of the power switching element and shutting off the power switching element, the voltage detection means detects the high side voltage of the power switching element, and the detection of the voltage detection means a voltage comparator that detects a short circuit in any of the above by comparing the voltage with a reference voltage; and a voltage comparator that stops the operation of the drive circuit of the power switching element when any of the short circuits in the above are detected by the voltage comparator. A short circuit protection circuit comprising drive circuit control means. (2) The short-circuit protection circuit according to claim 1, which is implemented as a power IC. (3) The short circuit protection circuit according to claim 1 or 2, wherein the circuit constituted by the power switching element is an inverter.