JPH0662577A - Power device - Google Patents

Abstract

PURPOSE:To prevent rush current by a simple structure and to prevent re-rush current at the time of an instant stoppage of power, in a power device. CONSTITUTION:When turning on a commercial AC power supply 1, a switching element 8 is turned ON. Since a smoothing capacitor 3 having no storage of electric charge is nearly in a shorted condition, a large current tends to flow in a shunt resistor 5. However, when the current reaches a certain level, a light emitting diode 7a of a photo coupler 7 conducts and then a photo transistor 7b conducts and turns the switching element 8 OFF and thereby charging of the smoothing capacitor 3 is stopped. By repeating this operation, the smoothing capacitor 3 is charged little by little, with a peak of rush current being controlled. The current just after rectification is detected at real time and the charging current of the smoothing capacitor is controlled, so rush current can be prevented in a simple circuit configuration.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device for converting a commercial AC power supply into a direct current.

[0002]

2. Description of the Related Art A conventional inrush current prevention circuit for a power supply device will be described below with reference to FIG.

FIG. 3 is a circuit diagram showing a rush current prevention circuit of a conventional power supply device. Reference numeral 1 is a commercial AC power supply, 2 is a diode bridge for rectification, and 3 is a smoothing capacitor. The voltage of the AC power supply 1 is rectified by the diode bridge 2, further smoothed by the smoothing capacitor 3, and a DC voltage is applied to the load device 4. Is being supplied. Reference numeral 11 is a rush current prevention resistor, and 12 is a relay for short-circuiting both ends of the rush current prevention resistor 11. Reference numeral 13 is a relay power supply circuit that generates a voltage for driving the relay 12, and 14 is a relay 12
It is a circuit that controls the opening and closing of.

The operation of the power supply device configured as described above will be described. When the commercial AC power supply 1 is turned on, the smoothing capacitor 3 having no charge accumulation is in a state close to a short circuit, so that a large amount of current tends to flow through the diode bridge 2. However, since the inrush current prevention resistor 11 is inserted, the current is inversely proportional to the resistance value. Therefore, if the value of the inrush current prevention resistor 11 is appropriately selected, the peak of the inrush current when the power is turned on can be suppressed to some extent. Unless the peak of the inrush current is suppressed to some extent, the breaker, fuse, etc. may be cut off.

Next, when the smoothing capacitor 3 is charged,
A voltage for driving the relay is generated by the relay power supply circuit 13, and the relay 12 is closed through the relay control circuit 14. Since the current thereafter flows by bypassing the inrush current prevention resistor 11, the heat generation of the inrush current prevention resistor 11 is limited when the power is turned on.

As described above, in the conventional inrush current prevention circuit, the peak value of the current immediately after the power is turned on is determined by the large inrush current prevention resistor 1.
After being pressed by 1, the relay 12 is turned "on" to start normal operation.

[0007]

Such a conventional inrush current prevention circuit for a power supply device requires a power supply and a control circuit for driving a relay, which complicates the circuit and increases the cost. Also, in the case of an instantaneous power failure of the commercial AC power supply, the voltage of the commercial AC power supply may drop once and the relay may immediately recover without being turned off.In such a case, re-rush current flows through the relay, There was a problem that the peak of the current was large.

The present invention is intended to solve the above problems, and it is an object of the present invention to prevent an inrush power source with a simple circuit configuration and solve the problem of re-inrush current at the time of momentary power failure.

[0009]

In order to solve the above problems, the inrush current prevention circuit of the power supply device of the present invention shuts off the line connected to the shunt resistor for detecting the current value immediately after rectification and the smoothing capacitor. A line for connecting a smoothing capacitor by driving a light emitting diode (light emitting element) of a photocoupler in parallel with a shunt resistor and driving the switching element according to the output signal of the light receiving element of the photocoupler. Configured to shut off.

[0010]

With the above structure, when a current flows through the shunt resistor, a voltage proportional to the current is generated across the shunt resistor. Then, when the voltage value exceeds a certain value, the light emitting diode of the photocoupler becomes conductive, and the switching element connected in series with the smoothing capacitor is turned "off" by the output signal of the light receiving element of the photocoupler. Then, charging of the smoothing capacitor is stopped and the inrush current is limited.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 is a circuit diagram showing an embodiment of the inrush current prevention circuit of the present invention. In FIG. 1, reference numeral 1 denotes a commercial AC power source, which is rectified by a diode bridge 2. Further, it is smoothed by the smoothing capacitor 3, and a DC voltage is supplied to the load device 4. Reference numeral 5 is a shunt resistor inserted between the diode bridge 2 and the smoothing capacitor 3. A voltage proportional to the flowing current is generated across the shunt resistor 5. Reference numeral 6 is a resistor that divides the voltage generated across the shunt resistor 5 and sets the detected current value.

Reference numeral 7 is a photocoupler. Reference numeral 7a is a light emitting diode of the photocoupler 7, and 7b is a phototransistor of the photocoupler 7. The light emitting diode 7a conducts and emits light when the voltage exceeds a certain voltage, and the phototransistor 7b receives the light. A switching element 8 is connected in series with the smoothing capacitor 3. The phototransistor 7b is connected between the base of the switching element 8 and GND. Reference numeral 9 is a feedback diode, and a current flows through the feedback diode 9 when the smoothing capacitor 3 is discharged. Reference numeral 10 is a base resistor for supplying a predetermined current to the base of the switching element 8.

The operation will be described below. Commercial AC power supply 1
When is turned on, a current flows through the base resistor 10 and the switching element 8 is turned “on”. Then, since the smoothing capacitor 3 having no charge accumulated is in a state close to a short circuit, a large amount of current tries to flow through the shunt resistor 5. However, when a certain current value is reached, the light emitting diode 7a of the photocoupler 7 conducts and emits light, and accordingly the phototransistor 7b
Conducts to short-circuit the base of the switching element 8 to GND. Then, the switching element 8 is turned "off", and the charging of the smoothing capacitor 3 is stopped.

When the current flowing through the shunt resistor 5 becomes smaller than a certain value, the light emitting diode 7a and the phototransistor 7b are turned "off" and the switching element 8 is turned "on" again.

By repeating the above operation, it becomes possible to gradually charge the smoothing capacitor 3 while suppressing the peak of the inrush current.

The voltage (Vc) at point A immediately after the power is turned on in FIG.
The waveform of the current (Ic) flowing through the smoothing capacitor 3 is shown in FIG. In other words, when a current exceeds the current limit value level, the transistor 8 connected in series to the smoothing capacitor 3 is turned off, so that no more current flows. Further, when the current falls below the limit value level, charging of the smoothing capacitor 3 starts again. Thus, the waveform of the current flowing to the smoothing capacitor 3 has a trapezoidal shape.

With such a structure, the current value rating of the diode bridge 2 can be lowered, which has the advantage of cost reduction. Further, a power supply device for high power has a breaker connected between the commercial AC power supply 1 and the diode bridge 2. However, if the peak value of the current is low as shown in the above embodiments, the current value rating of the breaker is lowered. It is possible to reduce the total cost.

Further, as shown in FIG. 2, the smoothing capacitor 3
The waveform of the current flowing to is trapezoidal, and the current flows for a long time during a half cycle of the voltage. In this embodiment, since the current flows in this way, the power factor when the power supply device is viewed from the power supply side can be improved.

[0020]

As described above, according to the present invention, since the current immediately after rectification is detected in real time and the charging current of the smoothing capacitor is controlled by the value, the inrush current can be prevented with a simple circuit configuration. Therefore, cost reduction can be realized. Furthermore, the re-rush current at the moment of a power failure, which is a problem with the relay method, can be suppressed.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a rush current prevention circuit of a power supply device according to an embodiment of the present invention.

FIG. 2 is a waveform diagram showing the operation of the inrush current prevention circuit of the same embodiment.

FIG. 3 is a circuit diagram showing a rush current prevention circuit of a conventional power supply device.

[Explanation of symbols]

 1 AC power supply 2 Diode bridge 3 Smoothing capacitor 4 Load 5 Shunt resistance 6 Voltage dividing resistance 7 Photocoupler 7a Light emitting diode 7b Phototransistor 8 Switching element 9 Feedback diode 10 Base resistance

Claims (2)

[Claims] 1. A rectifying means for rectifying an AC voltage, a smoothing capacitor for smoothing the voltage rectified by the rectifying means to supply a DC voltage to a load device, and a current flowing from the rectifying means to the smoothing capacitor. And a switching element connected in series with the smoothing capacitor, and configured to open and close the switching element according to a detection output of the current detecting means. 2. The power supply device according to claim 1, wherein the current detecting means is composed of a resistor and a photocoupler connected in parallel with the resistor.