JPS6051415A - Burnout loss protecting circut of rush-current limiting resistor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION la) Technical Field of the Invention The present invention relates to a burnout protection circuit for an inrush current limiting resistor in a power rectifying and smoothing circuit.

Background of the technology Conventionally, the DC power supplied to electronic equipment has been supplied by converting the commercial power supply using a transformer, then directly rectifying it to DC using a power rectification and smoothing circuit consisting of a rectifying element and a capacitor. , the control circuit turns on and off the gate of the switching element to turn the DC power rectified into a one-end plane current into an intermittent DC wave, which is then converted into an intermittent DC wave by the next-stage transformer. There are methods such as converting the power, rectifying it in the next power rectification and smoothing circuit, and supplying it. Recently, as the load capacity of electronic equipment has increased, there has been an increase in demand for high-power, low-voltage DC power supplies.The former requires large power supplies and is only used for small power applications, while high-power, low-voltage DC power supplies are The latter method is mainly used because it has the advantage that the power supply voltage can be easily controlled.

In the latter supply method, a large capacity capacitor is used as the capacitor of the first stage power rectification and smoothing circuit, and an excessive rush current flows when the power is turned on. In order to limit the inrush current, an inrush current limiting resistor is inserted in series with a large capacity capacitor.7 The power is turned on while limiting the inrush current, and after the capacitor is fully charged, a thyristor etc. is inserted to short the inrush current limiting resistor. It is a provision. In addition, in these circuits, there is a risk that the thyristor etc. will not work and the inrush current limiting resistor will overheat and burn out, so a burnout protection circuit for the inrush current limiting resistor is generally installed to prevent the inrush current limiting resistor from burning out. It is provided.

10) Prior Art and Problems A conventional burnout protection circuit for an inrush current limiting resistor of this type will be explained. FIG. 1 shows a block diagram of a conventional inrush current limiting resistor burnout protection circuit configuration. Turn on the power switch 1, apply commercial power, and connect the four rectifying elements 2a---2.
6 performs full-wave rectification and charges the large capacitor 3. The large-capacity capacitor 3 is gradually charged by the inrush current limiting resistor 4 that prevents an excessive inrush current when the power is turned on. After charging of the large capacity capacitor 3 is completed, the thyristor 5 is turned on to short-circuit the inrush current limiting resistor 4. Next, the electric charge of the large capacity capacitor 3 is discharged, charging of the large capacity capacitor 3 is started again, the thyristor 5 is turned off, the rush current limiting resistor 4 is enabled, and the large capacity capacitor 3 is gradually charged.

The above operations are repeated while power is supplied.

If the thyristor 5 does not turn on even after the large capacity capacitor 3 has been charged due to a failure of the thyristor 5 caused by some abnormality, current will continue to flow through the inrush current limiting resistor 4 and the inrush current limiting resistor will 4 rises, the temperature switch 6 that detects the temperature of the inrush current limiting resistor 4 is activated, the monitoring circuit 7 that monitors the temperature switch 6 is activated, and the monitoring circuit 7 opens the closing switch 1. An inrush current limiting resistor burnout protection circuit is provided to prevent the inrush current limiting resistor 4 from burning out. However, this burnout protection circuit
Since it operates by detecting the temperature of the inrush current limiting resistor 4, it has the disadvantage that the detection time is slow and it is easily influenced by the ambient temperature.

(dl OBJECT OF THE INVENTION The present invention aims to solve this conventional drawback.

fil Structure of the Invention The above object is to provide a capacitor that charges a current rectified by a rectifying element that rectifies an AC power supply, an inrush current limiting resistor that limits inrush current to the capacitor when the power is turned on;
In a power supply rectifying and smoothing circuit including a short circuit that shorts the inrush current limiting resistor after charging of the capacitor is completed,
A voltage detection circuit for detecting a voltage across the inrush current limiting resistor is provided at both ends of the inrush current limiting resistor, and when the short circuit does not operate, the voltage detecting circuit operates to protect the inrush current limiting resistor. This is achieved by the present invention configured as described above.

That is, due to the current flowing through the inrush current limiting resistor.

A voltage detection circuit that detects the voltage generated at both ends is provided, and this voltage detection circuit detects an abnormality and activates the monitoring circuit.Since the voltage at both ends of the inrush current limiting resistor is detected, the detection time is quick and the detection time is fast. The present invention provides a burnout protection circuit for an inrush current limiting resistor that is not affected by temperature.

(fl Embodiment of the Invention An embodiment of the present invention will be described below. Figure 2 shows a block diagram of the burnout protection circuit configuration of the inrush current limiting resistor according to the present invention. In the two figures, the same object is shown in Figure 1. 8 is a voltage detection circuit, and the voltage detection circuit 8 is a constant current circuit consisting of a transistor 9 and a Zener diode 10, and a light emitting diode of a photocoupler 11 is connected to the emitter side of the transistor 9. The monitor circuit 7 is configured to receive light emitted by a phototransistor and operate the monitoring circuit 7.

The normal operation in FIG. 2 is the same as the previous description, so it will be omitted. If the thyristor 5 does not turn on even after the large capacity capacitor 3 has been charged due to a failure of the thyristor 5 caused by some abnormality, the inrush current limiting resistor 4
The current tries to continue to flow, but the inrush current limiting resistor 4
An abnormality is detected by the voltage detection circuit 8 that detects the voltage across the
The photocoupler 11 of the voltage detection circuit 8 is activated, the monitoring circuit 7 is activated, and the closing switch 1 is opened, thereby preventing the inrush current limiting resistor 4 from burning out. The detection sensitivity of the voltage detection circuit 8 may be selected based on the circuit constants of the voltage detection circuit 8 and the inrush current limiting resistor 4.

(gl As described in detail of the invention, by providing the inrush current limiting resistor of the power supply rectifying and smoothing circuit with a voltage detection circuit that detects the voltage across the inrush current limiting resistor according to the present invention, the inrush current limiting resistor is short-circuited. If the short circuit does not turn on, the voltage detection circuit detects an abnormality, opens the closing switch, and detects the voltage across the inrush current limiting resistor, so the detection time is quick and the inrush current is not affected by ambient temperature. This has the effect of protecting the limiting resistor from burning out.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional burnout protection circuit for an inrush current limiting resistor, and FIG. 2 is a block diagram of a burnout protection circuit for an inrush current limiting resistor according to the present invention. In the drawing, ■ is a closing switch, 2a to 2d are rectifying elements, 3 is a large capacitor, 4 is an inrush current limiting resistor, 5 is a Zyristor, 7 is a monitoring circuit, 8 is a voltage detection circuit,
11 indicates a po] coupler, respectively. Japan Figure 1 Figure 2 Figure 81-

Claims (1)

[Claims] A capacitor that charges a current rectified by a rectifying element that rectifies an AC power supply, an inrush current limiting resistor that limits inrush current to the capacitor when the power is turned on, and 9 short-circuiting the inrush current limiting resistor after charging of the capacitor is completed. In the power supply rectifying and smoothing circuit including a short circuit, a voltage detection circuit is provided at both ends of the inrush current limiting resistor to detect a voltage across the inrush current limiting resistor, and when the short circuit is not activated, the voltage detecting circuit A burnout protection circuit for an inrush current limiting resistor, characterized in that it is configured to operate.