JPS6353772B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a short circuit detection circuit, and includes, for example, an electroplating circuit using a semiconductor element, etc.
Alternatively, it can be used in the same current rectifier such as alumite treatment.

A conventional device of this type is shown in FIG. In the figure, 1 is a switch, 2 is a rectifier transformer, 3 is a rectifier, and 4 is a current detector that generates a DC voltage proportional to the output current, which is connected in series to a load 6. 5 is a current control device that compares the voltage obtained from the current detector 4 with a reference value and includes an operational amplifier that controls the rectifier 3, and generates a trip signal that opens the switch 1 in the event of overcurrent; is the load.

Next, the operation of the short circuit detection device will be explained.

First, a case where a short circuit occurs while the load is energized will be explained.
When both ends of the load 6 are short-circuited and an overcurrent flows, the current detector 4 generates a voltage proportional to the overcurrent.
This voltage is compared with a reference value by the current control device 5, and when the current control device 5 detects an overcurrent, it issues a control signal to the rectifier 3 to throttle the current, and also sends a trip signal to the switch 1. broth,
Cuts off the load current.

Next, a case will be described in which energization of the load 6 is started in a short-circuited state before load energization.

When power is started with the load short-circuited and constant current control is performed, the overcurrent does not suddenly flow as in the case of a short circuit while the load is being energized, but instead flows gradually, so the current stops flowing sooner than the current control circuit 5 detects the overcurrent. Since a control signal is generated to throttle the rectifier, power continues to be supplied to the load as if it were normal, and although the rectifier is not damaged, the load current flows into surrounding machinery and equipment, causing damage. There was a drawback.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above.By simultaneously detecting the output voltage and output current, it is possible to reliably detect load short circuits and prevent damage to surrounding machinery and equipment. It is an object of the present invention to provide a short circuit detection device that prevents short circuits from occurring.

Hereinafter, this invention will be explained based on FIG. 2.

In FIG. 2, the same or equivalent components as in FIG. 1 are given the same reference numerals, and redundant explanation will be omitted.

In FIG. 2, 7 is a voltage detector that generates a DC voltage proportional to the output voltage, and is connected in parallel to the load 6. Reference numeral 8 denotes a load short circuit detection circuit which outputs an output signal regardless of the deviation value if the output of the current detector 4 is above a predetermined value and the output of the voltage detector 7 is below a predetermined value. A current detector 4 and a voltage detector 7 are connected to the input side of the detector. 9 is a short circuit detection device that includes a current detector 4, a voltage detector 7, and a load short circuit detection circuit 8.

The operation of this invention will be explained with reference to FIGS. 2 and 3.

FIG. 3 shows the operation of the load short circuit detection circuit 8, in which the horizontal axis represents the output of the current detector 4, and the vertical axis represents the output of the voltage detector 7. A1 is a predetermined current value of the current detector 4, and V1 is a predetermined voltage value of the voltage detector 7. The load short-circuit detection circuit 8 has a load short-circuit range as indicated by diagonal lines, which is a predetermined current value A1 or more and a predetermined voltage value V1 or less, and when the outputs of the current detector 4 and voltage detector 7 fall within this range, The load short-circuits and gives an output signal. Based on the output signal of the current control device 5, a control signal is sent to the rectifier 3 to throttle the current, and a trip signal is sent to the switch 1 to cut off the load current.

A rectifier with such an operation can detect a short circuit and cut off the load current, regardless of whether the short circuit occurs while the load is energized or before the load is energized.

Next, a specific example of the short circuit detection device shown in FIG. 4 will be explained.

This device uses a current detection differential amplifier 10 and a voltage detection differential amplifier 1 to detect a predetermined current value A1 and a predetermined voltage value V1.
It is set by the level setting resistor built into 1.

When the rectifier 3 is short-circuited and the output of the current detector 4 becomes more than the predetermined current value A1 and the output of the voltage detector 7 becomes less than the predetermined voltage value V1, the current detection differential amplifier 10 and the voltage detection differential amplifier The output of the device 11 becomes positive, and the AND circuit 12 outputs an output signal regardless of the deviation value of these outputs. Therefore, the switching transistor 13 is turned on, causing current to flow through the relay coil 14, and the relay contact 15 is turned on, thereby sending a signal to the current control device 5.

Next, if there is no short circuit, even if the output of the current detector 4 is higher than the current predetermined value A1, the voltage detector
Since the output of the current detection differential amplifier 10 is positive and the output of the voltage detection differential amplifier 11 is negative, the AND circuit 12 does not output an output signal. Therefore, relay contact 15
is not turned on.

In addition, although the short circuit detection circuit of a current control rectifier was explained in the said Example, if it is a current control apparatus, the same effect as the said Example will be produced.

As described above, according to the present invention, the voltage and current applied to the load are detected, and a load short circuit can be reliably detected regardless of a short circuit during energization or a short circuit before energization, so that the device is safe. This eliminates the disadvantage that load current flows into and damages surrounding machinery and equipment.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a conventional device, FIG. 2 is a circuit diagram showing an embodiment of the present invention, and FIG. 3 is an output voltage-current characteristic and an operating range of the load short-circuit detection circuit 8 in normal and abnormal states. FIG. 4 is a circuit diagram of a short circuit detection device according to an embodiment of the present invention. In the figure, 1 is a switch, 2 is a rectifier transformer, 3 is a rectifier, 4 is a current detector, 5 is a current control device, 6 is a load, 7 is a voltage detector, 8 is a short circuit detection circuit, and 9 is a short circuit Detection device, 10 is a current detection differential amplifier, 11 is a voltage detection differential amplifier, 12 is AND
circuit, 13 is a switching transistor, 14
is the relay coil, 15 is the relay contact, A1, V
1 is a predetermined current value and a predetermined voltage value of the short circuit detection circuit. In addition, each same code|symbol shows the same or equivalent part.

Claims (1)

[Claims] 1 a current detector that detects the output current of the rectifier;
a voltage detector that detects the output voltage of the rectifier;
A current detection differential amplifier outputs a positive output when the output of the current detector is above a predetermined value, and a voltage detection differential amplifier outputs a positive output when the output of the voltage detector is below a predetermined value. Control that generates an output signal regardless of the deviation value based on the positive output from the rectifier, the current detection differential amplifier, and the voltage detection differential amplifier, and throttles the current of the rectifier using the current control device. A short circuit detection device equipped with an AND circuit that outputs a signal and also causes a switch to output a trip signal.