JPH0454863A - Rush current limiter - Google Patents

Abstract

PURPOSE:To suitably control a timing for short-circuiting a rush current limiting resistor by composing the resistor, voltage detecting means, and control means for controlling to short-circuit both ends of the resistor. CONSTITUTION:Since a rush current flows to a resistor 4 at the time of turning ON a power source, a voltage at both ends is raised. The values of resistors 61, 62 and Zener voltage of a Zener diode 64 are previously set to predetermined values so that the diode 64 is turned ON. The diode 64 is turned ON at the initial time, and a photocoupler 66 is turned ON. A thyristor 5 is turned OFF during this period. When the rush current is reduced, a voltage across the resistor 4 is sufficiently lowered, and the diode 64 is turned OFF, the photocoupler 66 is also turned OFF, and a control signal for turning ON the thyristor 5 is generated from a stabilizer 9.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD The present invention relates to an inrush current limiting circuit, and more particularly to a circuit for limiting inrush current when power is turned on in a power supply circuit device.

Prior Art A conventional circuit of this type is shown in FIG. The AC voltage from the AC input power supply terminal 1.2 is rectified by the rectifier circuit 3.

This rectified output 12 is supplied to a stabilizing circuit 9 having a smoothing capacitor 91 and becomes a predetermined DC voltage to the output terminal 1.
0.11.

A resistor 4 for limiting rush current is inserted in series with the output of the rectifier circuit 3, and a thyristor 5 as a switching element is connected to both ends of this resistor. This thyristor 5 is controlled by a stabilizing circuit 9.

FIG. 3 is an operation waveform diagram for explaining the inrush current limiting mode. First, when the AC input power source is turned on, the inrush current is limited via the inrush current limiting resistor 4. At the same time, the smoothing capacitor 91 of the stabilizing circuit 9 is gradually charged, and its terminal voltage rises as shown in the waveform before improvement in FIG.

Then, after a predetermined period of time, a control signal for turning on the thyristor 5 is generated from the stabilizing circuit 9, and the current limiting resistor 4 is short-circuited to enter the normal operating state.

In this case, the smoothing capacitor 91 in the stabilizing circuit 9 is set to a large value in consideration of the instantaneous power failure resistance of the power supply circuit, and therefore it takes time for the output voltage of the capacitor to reach a predetermined value. , the stabilizing circuit 9 is fixedly designed in advance to generate a control signal for turning on the thyristor 5. As a result, as shown in the waveform of FIG. 3, a large inrush current flows at the moment the thyristor turns on, which is undesirable.

This is because the charging voltage of the smoothing capacitor 91 is not monitored, and as mentioned above, in order to ensure sufficient momentary interruption resistance, the thyristor is turned on before the terminal voltage of the smoothing capacitor rises sufficiently. This is due to a number of reasons.

Purpose of the Invention The present invention has been made to solve the drawbacks of the conventional ones, and its purpose is to completely control the inrush current by appropriately controlling the timing of short-circuiting the inrush current limiting resistor. An object of the present invention is to provide a limitable inrush current limiting circuit.

According to the present invention, there is provided an inrush current limiting circuit for a power supply device having a smoothing circuit for smoothing an input power source, the inrush current limiting resistor being inserted into the input of the smoothing circuit, and the voltage across the resistor being An inrush current limiting circuit is obtained, which includes a voltage detecting means for detecting the voltage, and a control means for short-circuiting both ends of the current limiting resistor when the detected voltage reaches a predetermined value.

Example The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a circuit diagram of an embodiment of the present invention, and parts equivalent to those in FIG. 2 are designated by the same symbols. An inrush current monitoring circuit 6 is provided that detects the voltage across the current limiting resistor 4 and generates a detection signal when this voltage reaches a predetermined value, and a stabilizing circuit 9 responds to the generation of this detection signal. is configured to turn on the thyristor 5.

This inrush current monitoring circuit 6 inputs voltage dividing resistors 61 and 62 that divide a voltage proportional to the magnitude of the inrush current flowing through the resistor 4, a capacitor 63 that smoothes this divided voltage and output, and a divided voltage output. a Zener diode 64, a bias resistor 65 for this diode 64, and a photocoupler element 6 that is turned off by the output of the Zener diode 64.
6.

The output of this photocoupler element 66 is input to the stabilizing circuit 9, and the thyristor 5 is turned on in response to this output.

When the power is turned on, a rush current flows through the resistor 4 as shown in the waveform of FIG. 3, so the voltage across the resistor 4 becomes large. Therefore, the values of the resistors 61 and 62 and the Zener voltage of the Zener diode 64 are set in advance to predetermined values so that the Zener diode 64 is turned on.

Therefore, at the initial stage, the Zener diode 64 is on, and the photocoupler 66 is also on. During this time, the thyristor 5 is in an off state.

Then, when the inrush current decreases and the voltage across the resistor 4 becomes sufficiently low and the Zener diode 64 turns off, the photocoupler 66 also turns off, and the stabilizing circuit 9 generates a control signal to turn on the thyristor 5. It is.

The waveform diagram after the improvement in Figure 3 shows the state at that time, and by setting the resistor 61, 62 and Zener voltage,
It becomes possible to reduce the inrush current when the thyristor 5 is turned on to a specified value or less.

Note that the thyristor 5 can be replaced with another switching control element.

Effects of the Invention As described above, according to the present invention, the inrush current when the input power is turned on is monitored and the short-circuit timing of the inrush current limiting resistor is controlled, so the inrush current can be limited within a specified value. There is an effect.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, FIG. 2 is a diagram illustrating a conventional inrush current limiting circuit, and FIG. 3 is an operating waveform diagram of the inrush current limiting circuit. Explanation of symbols of main parts 3... Rectifier circuit 4... Inrush current limiting resistor 5... Thyristor 6... Inrush current monitoring circuit 9...・Stabilization circuit

Claims (1)

[Claims] (1) An inrush current limiting circuit for a power supply device having a smoothing circuit for smoothing an input power supply, the inrush current limiting resistor being inserted into the input of the smoothing circuit, and voltage detection means for detecting the voltage across the resistor. , and control means for short-circuiting both ends of the current limiting resistor when the detected voltage reaches a predetermined value.