JPH04312314A - Overcurrent protection circuit - Google Patents

Abstract

PURPOSE:To detect such overload state as a rated load exceeds slightly and continuously for a long time. CONSTITUTION:Overcurrent detecting circuits 4a, 4b have different overcurrent detecting levels iOV1, iOV2 and make decision of overcurrent based on an analog signal fed from a current detecting circuit 2. Overcurrent timer circuits 5a, 5b correspond, respectively, to the overcurrent detecting circuits 4a, 4b and measure overcurrent intervals. When thus measured intervals exceed preset intervals, a power supply inhibition command is fed to a power supply control circuit 3.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overcurrent protection circuit, and more particularly to power supply control against power system failures.

0002

2. Description of the Related Art As shown in FIG. 5, a conventional overcurrent protection circuit includes one overcurrent detection circuit 2' having one overcurrent setting value for each power supply output, and one overcurrent detection circuit 2' having one overcurrent setting value for each power supply output. It has a power supply control circuit 3 that controls the supply of power.

The overcurrent detection circuit 2' monitors the load current based on one overcurrent setting value, and when it detects a load current exceeding the overcurrent setting value, temporarily outputs an output to the power supply control circuit 3. Instructs to stop or suppress output.

The operation of the conventional overcurrent protection circuit shown in FIG. 5 will be explained with reference to FIG.

[0005] The overcurrent detection circuit 2' has a rated current level i.
It has an overcurrent detection level iov (overcurrent setting value) greater than c. When the load current becomes larger than the overcurrent detection level iov, the overcurrent detection circuit 2' issues an instruction to temporarily stop power supply, as shown by the solid line in FIG. 6b), or instructs the power supply to be temporarily stopped, as shown by the broken line in FIG. 6b). Outputs current limit instructions.

[0006]

As described above, the conventional overcurrent protection circuit monitors the load current based on one overcurrent setting value, and when an excess current is detected within a certain period of time, Output is temporarily stopped or suppressed. The overcurrent setting value has been set to a value with sufficient margin for the rated load supply current value, taking into account various load conditions.

For this reason, there is a problem in that overload cannot be detected in the event of a specific fault, for example, in the event of a fault that slightly exceeds the rated load and has been left unused for a long time.

An object of the present invention is to provide an overcurrent protection circuit capable of detecting an overload condition that slightly exceeds the rated load and continues for a long time.

[0009]

[Means for Solving the Problems] The overcurrent protection circuit according to the present invention includes a plurality of overcurrent detection circuits having different overcurrent setting values, and measures different overcurrent times corresponding to the plurality of overcurrent detection circuits. and multiple overcurrent timing circuits that output alarms,
A power supply control circuit that performs a plurality of power supply controls in response to the outputs of the plurality of overcurrent timing circuits.

0010

Embodiments Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows an overcurrent protection circuit according to an embodiment of the present invention.

The overcurrent protection circuit according to this embodiment includes a DC power generation section 1, a current detection circuit 2, and a power supply control circuit 3.
, first and second overcurrent detection circuits 4a and 4b, and a first
and second overcurrent timing circuits 5a and 5b.

The power supply control circuit 3 includes a DC power generation section 1
This is a circuit that controls on/off the supply of DC power from the DC power source, as will be described later.

The power supply control circuit 3 performs the following two types of supply suppression based on overcurrent detection information.

(2) Stopping power supply only during the period when overcurrent occurs.

(2) Stop the power supply from the time when overcurrent occurrence is detected until the power input is turned off.

The current detection circuit 2 is a circuit that generates an analog signal having a level corresponding to the load current.

First and second overcurrent detection circuits 4a and 4
b are respectively different first and second overcurrent detection levels io
This circuit has v1 and iov2 and performs overcurrent determination based on the analog signal from the current detection circuit 2.

As shown in FIG. 2, both the first and second overcurrent detection levels iov1 and iov2 are greater than the rated current level ic, and the first overcurrent detection level iov1 is higher than the second overcurrent detection level. Greater than level iov2.

First and second overcurrent timing circuits 5a and 5
b measures the first and second overcurrent occurrence periods corresponding to each of the first and second overcurrent detection circuits 4a and 4b, and determines the first and second regulations determined in advance for each. When the time has elapsed, first and second power supply suppression instructions are output to the power supply control circuit 3.

FIG. 2 shows a time chart for explaining the operation of the embodiment shown in FIG.

In FIG. 2, the delay time t11 or t21
respectively indicate the determination time of overcurrent occurrence in the first and second overcurrent detection circuits 4a and 4b with respect to a change in load current, and the delay time t12 or t22 is, respectively,
The delay time when overcurrent is released in the first and second overcurrent detection circuits 4a and 4b is shown. Furthermore, the broken line portion indicates the operating state when the power supply control circuit 3 performs current limiting control instead of stopping supply.

FIG. 3 shows the power supply control circuit 3.

The power supply control circuit 3 includes a relay contact 31, a relay drive unit 32, a signal synthesis circuit 33, a flag circuit (flip-flop) 34, and an input power on/off detection circuit (POR) 35. .

Referring to FIG. 4, the operation of the power supply control circuit 3 will be explained.

While the first power supply suppression instruction signal of logic "1" is being supplied to the relay drive section 32 via the signal synthesis circuit 33, the relay drive section 32 opens the relay contact 31.

On the other hand, when the second power supply suppression instruction signal of logic "1" is supplied, the flag circuit 34 is set;
The flag circuit 34 outputs a logic "1" signal. This logic “1” signal is supplied to the relay drive section 32 via the signal synthesis circuit 33. In response to this logic "1" signal, the relay drive section 32 opens the relay contact 31. When the input power on/off detection circuit 35 detects that the input power is turned off, the input power on/off detection circuit 35 supplies a logic "0" signal to the flag circuit 34, and the flag circuit 34 is reset. The flag circuit 34 outputs a logic "0" signal. This logic “0” signal is supplied to the relay drive section 32 via the signal synthesis circuit 33. In response to this logic “0” signal, the relay drive section 32 closes the relay contact 31.

[0028]

[Effects of the Invention] As explained above, according to the present invention, it is possible to detect an overload state that slightly exceeds the rated load and continues for a long time due to a unique fault other than a load short circuit, and the power supply This has the effect of providing circuit protection such as shutdown.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an overcurrent protection circuit according to an embodiment of the present invention.

FIG. 2 is a time chart for explaining the operation of the embodiment shown in FIG. 1;

FIG. 3 is a block diagram showing the power supply control circuit in FIG. 1;

FIG. 4 is a time chart for explaining the operation of the power supply control circuit shown in FIG. 3;

FIG. 5 is a block diagram showing a conventional overcurrent protection circuit.

6 is a time chart for explaining the operation of the overcurrent protection circuit shown in FIG. 5. FIG.

[Explanation of symbols]

1 DC power generation section 2 Current detection circuit 3 Power supply control circuit 4a, 4b Overcurrent detection circuit 5a, 5b Overcurrent clock circuit 31 Relay contact 32 Relay drive section 33 Signal synthesis circuit 34 Flag circuit 35 Input power supply on/off detection circuit

Claims (3)

[Claims] [Claim 1] A plurality of overcurrent detection circuits having different overcurrent setting values and performing overcurrent detection based on each overcurrent setting value, and a plurality of overcurrent detection circuits having different overcurrent times corresponding to the plurality of overcurrent detection circuits. and a power supply control circuit that performs a plurality of power supply controls in response to the outputs of the plurality of overcurrent timer circuits. protection circuit. 2. The power supply control circuit is configured to stop the power supply only during the overcurrent occurrence period or to continue the power supply from the time when the overcurrent occurrence is detected until the power input is turned off, according to the outputs of the plurality of overcurrent timing circuits. The overcurrent protection circuit according to claim 1, wherein the overcurrent protection circuit controls the power supply to either stop or stop the power supply. 3. A current detection circuit that generates an analog signal having a level corresponding to the load current, and a first overcurrent detection level, and performs overcurrent determination based on the analog signal from the current detection circuit. A second overcurrent detection circuit has a first overcurrent detection circuit and a second overcurrent detection level that is smaller than the first overcurrent detection level, and makes an overcurrent determination based on an analog signal from the current detection circuit. Corresponding to each of the current detection circuit and the first and second overcurrent detection circuits, the first and second overcurrent occurrence periods are measured, and the predetermined first and second overcurrent detection circuits are respectively measured. When the stipulated time is exceeded, the first
and first and second overcurrent timing circuits that output a second power supply suppression instruction, and first and second power supply corresponding to the outputs of the first and second overcurrent timing circuits, respectively. An overcurrent protection circuit comprising: a power supply control circuit that performs control;