JPH03154908A - Rush current preventing circuit - Google Patents

Abstract

PURPOSE:To limit the rush current and to prevent the breakage of parts of a primary circuit by forcibly turning off a relay connected in parallel with a rush current limiting resistance simultaneously with the turn-off of an AC switch. CONSTITUTION:The discharge of a rectifying chemical capacitor 15 is started simultaneously with the turn-off of an AC switch 11. Then, a rectifying diode 21 cuts off the upper part of a switching waveform outputted to the secondary side of a switching transformer 17 when the lower part of the switching waveform starts a rise. At the same time, the discharge of a rectifying chemical capacitor 22 is started through a discharge resistance 23. Thus, a discharging transistor 27 is turned on. As a result, the current to far flowed to the winding of a relay 14 flows to the transistor 27. Then, the relay 14 of a rush current limit resistor 13 can be turned off. Thus it is possible to surely limit the rush current in any state and to prevent the breakage of parts of a primary circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a rush prevention circuit composed of a rush current limiting resistor and a relay.

[Conventional technology]

Conventional rush current prevention @ circuits, as disclosed in Japanese Unexamined Patent Publication No. 588325, use the secondary output voltage to drive a relay connected in parallel with a rush prevention resistor, and the AC switch The relay operation when OFF was uncertain.

[Problem to be solved by the invention]

As mentioned above, in conventional rush current prevention circuits, a relay connected in parallel to a rush current limiting resistor is
It was driven using the secondary output voltage.

FIG. 2 is a circuit diagram showing such a conventional rush current prevention circuit.

In FIG. 2, when the AC switch 1 is turned on, a voltage rectified by the rectifying diode 2 and the rectifying chemi-con 5 is applied to the switching transformer 7, whereby the switching transistor 6 starts the switching operation on the primary side. A switching waveform is output to the secondary side of the switching transformer 7. This switching waveform is rectified by a rectifying diode 8 and a rectifying chemicon 9, and a load 10
is applied to the relay 4 connected in parallel with the rush current limiting resistor 3, and as a result, the relay 4 operates (ON) L.
Short-circuit the lash limiting resistor 3.

However, at this time, the relay 4 remains OFF until the secondary side output voltage rectified by the rectifying diode 8 and the rectifying chemical controller 9 reaches a certain specified voltage, and therefore the - secondary side rush current Because the rush current flows through the limiting resistor 3,
Rush current is limited.

Next, when the AC switch 1 is turned OFF, the operation of the switching 1-rangistaro stops after the electric charge of the rectifying chemi-con 5 is discharged, and after that, the switching waveform on the secondary side disappears, and the rectifying diode 8 and the rectifying Chemicon 9
rectification operation stops. After that, the rectifying chemicon 9
After the charge is discharged, the relay 4 is turned off. Therefore, even if the charge in the rectifying chemical controller 5 has been discharged, the relay 4 may remain on, and at that point the AC is turned on again.
When the switch 1 is turned on, the rush current does not flow through the rush limiting resistor 3 but flows through the relay 4, so that the rush current is not limited and there is a problem in that parts of the negative side circuit are destroyed.

The present invention aims to limit rush current under any conditions and prevent damage to components.

[Means to solve the problem]

In order to achieve the above object, the present invention detects the OFF state of the AC switch and outputs the secondary side output voltage (relay drive circuit).
Forcibly discharge the charge of and turn off the AC switch (
- At the same time as the next side rectifying chemical controller discharge start point), turn on the relay.
It is designed to cause FF.

[Effect]

The point at which the AC switch is turned off is the point at which the voltage of the primary side rectifying chemical controller starts to fall, and when the voltage starts to fall, the lower part of the switching waveform before secondary side rectification starts to rise. Utilizing this phenomenon, the upper part of the switching waveform is rectified to forcibly discharge the charge in the circuit used as the load power supply. This turns the AC switch off.
At the same time, the relay driven by the secondary output voltage can be turned off, and rush current can be reliably prevented under any condition.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG.

In FIG. 1, when the AC switch 11 is turned on, a voltage rectified by the rectifying diode 12 and the rectifying chemi-con 15 is applied to the switching transformer 17, and thereby the switching transistor 16 starts the switching operation on the primary side. , a switching waveform is output to the secondary side of the switching transformer 17. The upper part of this switching waveform is rectified by a rectifying diode 18 and a rectifying chemical controller 19, and is applied to a relay 14 connected in parallel with a load 20 and a rush limiting resistor 13. As a result, the relay 14 is activated (ON). ) Short-circuit the L rush limiting resistor 13. At this time, the relay 14 remains ○FFL until the secondary output voltage rectified by the rectifying diode 18 and the rectifying chemical controller 19 reaches a certain specified voltage.
- Since the next-side rush current flows through the rush limiting resistor 13, the rush current is limited.

Also, by using the lower part of the switching waveform output to the secondary side of the switching transformer 17, the rectifier diode 21
A negative voltage is generated by the rectifying chemical controller 22, and the capacitor 24 is charged with electric charge through the charging diode 25. At this time, the voltage at the cathode (point A) of the charging diode 25 is f90.7V (forward voltage of the charging diode 25), and the discharging transistor 27 is turned off.

Next, when AC switch 11 is set to ○FFL, 5
・ ・ 6 ・ At the same time as OFF, discharge of the rectifying chemical condenser 15 starts.

Then, even if the operation of the switching transistor 16 does not stop, the lower part of the switching waveform output to the secondary side of the switching transformer 17 starts to rise. Then, since the rectifier diode 21 and the rectifier chemicon 22 are a peak rectifier circuit, the rectifier diode 21 is cut off at the same time as the lower part of the switching waveform starts to rise. The electric charge in the rectifying chemical controller 22 starts to be discharged through the discharge resistor 23 from the time when the rectifying diode 21 is cut off, so that the voltage on the e side (point B) of the capacitor 24 starts to rise. Then, the Φ side (point A) of the capacitor 24 increases in proportion to the increased voltage at point B, and the charging diode 25
At the same time, switch diode 2 is cut off.
A base current is passed through the discharging transistor 27 through the discharging transistor 27, and the discharging transistor 27 is turned on. Therefore, the current that has been flowing through the winding of the relay 14 flows into the discharging transistor 27, and the relay 14 is turned off.

As explained above, at the same time that the AC switch 15 is turned off (at the time when the rectifying chemical controller 15 starts discharging), the relay 1
4 (for shorting the rush current limiting resistor 13)
F, and the rush current can be reliably limited under any conditions.

〔Effect of the invention〕

According to the present invention, the relay connected in parallel with the rush current limiting resistor can be forcibly turned off at the same time as the AC switch is turned off, so the rush current can be reliably limited under any conditions. It has the effect of preventing damage to circuit components.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a rush current prevention circuit as an embodiment of the present invention, and FIG. 2 is a circuit diagram showing a conventional rush current prevention circuit. 1.11...AC switch. 2.12... Rectifier diode. 3.13...Rush current limiting resistor. 4.14... Relay 5.15... Rectifier capacitor. 6.16...Switching transistor. 7.17...Switching transformer. 8.18... Rectifier diode. 9.19... Rectifier capacitor. 10.20...Load. 21...Detection voltage rectification diode. 22... Rectifier capacitor. 23...Discharge resistance. 24... Capacitor. 25... Charging diode. 26... Switch diode. 27...Discharge transistor.・9・

Claims (1)

[Scope of Claims] 1. A rush current limiting resistor disposed in a power supply circuit connected to an AC power source via an AC switch, into which the current flowing in the power supply circuit is input, and a rush current limiting resistor in parallel with the rush current limiting resistor. a relay connected to the AC, which short-circuits both ends of the rush current limiting resistor when turned on, and opens between both ends of the rush current limiting resistor when turned off;
From before the switch is turned on until a predetermined period of time has elapsed after the AC switch is turned on, the relay is turned off to reduce the rush current generated in the power supply circuit when the AC switch is turned on. In a rush current prevention circuit that limits the rush current by flowing it through a rush current limiting resistor, a detection means for detecting whether or not the AC switch is turned off is provided, and the detection means detects that the AC switch is turned off. A rush current prevention circuit characterized in that the relay is sometimes turned off.