JPH0619317Y2 - Inrush current limiting circuit for switching power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to an inrush current limiting circuit used in a switching power supply, and more specifically, a large current flows through an input capacitor of the switching power supply when the power is turned on. The present invention relates to an inrush current limiting circuit for preventing the above.

(Prior Art) FIG. 3 is a configuration connection diagram showing an example of a conventional inrush current limiting circuit used in a switching power supply. In the figure, 1 is an AC power supply, 2 is a rectifier circuit that converts AC from this AC power supply into DC, 31 and 32 are capacitors connected in series between the output terminals of this rectifier circuit 2, and T0 is the capacitors 31 and 32. Common connection point and common terminal C of rectifier circuit 2
With the terminal provided between the OMs, both terminals are short-circuited when the power supply 1 is AC100V system, and both terminals are open when it is AC200V system. Reference numeral 4 denotes a stabilizing circuit that inputs the rectified output voltage Ei obtained at both ends of the series circuit including the capacitors 31 and 32, switches and stabilizes the rectified output voltage Ei, and supplies the rectified output voltage Ei to a load. . Reference numeral 5 is a fuse inserted in the AC power supply line, 6 is a power switch, 7 is a noise filter that suppresses noise entering from the AC power supply 1 side, and 8 is an inrush current limiting circuit. The inrush current limiting circuit 8 includes a current limiting resistor 81 and
It is composed of a parallel circuit of a bidirectional switch (for example, triac or thyristor) 82. Reference numeral 9 denotes an auxiliary power supply including a converter for inputting the rectified output voltage Ei and supplying electric power for operating the stabilizing circuit 4, and uses the voltage e _A obtained from the auxiliary power supply to turn on the bidirectional switch 82. I have to.

(Problems to be solved by the invention) In the conventional inrush current limiting circuit having such a configuration, the bidirectional switch 82 is turned on before the power switch 6 is turned on and the output of the auxiliary power source 9 does not reach a constant value. It is turned off so that the current from the AC power supply 1 flows through the limiting resistor 81, and the input capacitors 31 and 32 are limited so that a large current does not flow. For this purpose, the input capacitors 31, 32
If the output of the auxiliary power supply becomes large before the battery is not sufficiently charged, the bidirectional switch 82 may be turned on.
In this case, the inrush current becomes large. In addition, the stabilization circuit 4
There is a problem that it is not synchronized with the operation of.

The present invention has been made in view of these problems, and its purpose is to determine the timing of turning on the bidirectional switch according to the charging state of the input capacitor.
The present invention intends to realize an inrush current limiting circuit that can reliably prevent a large current from flowing when the power is turned on.

(Means for Solving Problems) The present invention which solves the above problems is obtained by an AC power supply (1), a rectifier circuit (2) for converting AC from this AC power supply to DC, and a rectifier circuit. The rectified output voltage is input, the switching circuit stabilizes the rectified output voltage to supply power to the load, and the current limiting resistor and bidirectionality connected to the current circuit connecting the AC power supply and the rectifier circuit. An inrush current limiting circuit (8) which is connected in parallel or in series with a switch, and an auxiliary power supply (9) including a converter which inputs the rectified output voltage obtained by the rectifying circuit and supplies electric power for operating the stabilizing circuit. In a switching power supply device including a switch, a switch means (SW) or a primary coil configured by a photocoupler to obtain electric power obtained from the converter of the auxiliary power supply is connected via the switch means (SW). The transformer (8) connected to the secondary coil (n21) of the transformer of the barter
4) is provided with circuit means for supplying to the bidirectional switch, and the switch means (SW) is turned on when the output voltage of the stabilizing circuit reaches a constant value. It is a rush current limiting circuit for a switching power supply.

(Embodiment) FIG. 1 is a configuration connection diagram showing an example of a circuit according to the present invention. In the figure, the same elements as those of the circuit elements in FIG. 3 are designated by the same reference numerals. The auxiliary power supply circuit 9 here uses a ringing choke converter, and
1 is a transformer, Q1 is a switch element for turning on / off the rectified output voltage Ei and giving it to the primary winding n ₁₁ of the transformer 91, D1,
C1 is a circuit for rectifying and smoothing a voltage generated in the secondary winding n ₁₂ of the transformer 91, ZD is a Zener diode. Switching element Q1 in accordance with the difference between the reference voltage obtained from the output voltage and the Zener diode ZD of the rectifying and smoothing circuit on and off, the output of the secondary winding n ₂₁ is made to be a constant value corresponding to the reference voltage . The output of the secondary winding n ₂₁ is a diode D
2, it is supplied as the operating power of the stabilizing circuit 4 through the rectifying circuit composed of the capacitor C2.

In the inrush current limiting circuit 8, n ₂₂ is 2 of the transformer 91.
The next winding, D3 is a rectifying diode, and C3 is a smoothing capacitor. A stabilized DC voltage EA is obtained across the smoothing capacitor C3 by the switching operation of the switch element Q1. SW is a switch means provided between the gate of the bidirectional switch 82 and one end of the smoothing capacitor C3, and is composed of a photocoupler, and the stabilizing circuit 4
The output voltage E0 is turned on when the output voltage E0 reaches a constant value. The switch means SW supplies the voltage EA (electric power) obtained in the smoothing capacitor C3 to the bidirectional switch 82 or does not supply the voltage EA (electric power) to the bidirectional switch 82 from the secondary side of the transformer 91. It turns on and off.

The operation of the circuit thus constructed will be described below.

First, when the power switch 6 is not turned on, the converter 9 is not driven and the bidirectional switch 82
Is off.

Now, when the power switch 6 is turned on, the current from the AC power source 1 is applied to the rectifier circuit 2 via the current limiting resistor 81,
This rectifying circuit 2 forms a DC voltage to charge the input capacitors 31 and 32. Here, the bidirectional switch 8
2 is still off, so noise filter 7
The current from the AC power source 1 applied via the
Input capacitor 3 when power is turned on, limited by 1
It prevents an excessive inrush current from flowing to the terminals 1 and 32.

Voltage across input capacitors 31, 32 (rectified output voltage)
Ei gradually increases after the power switch 6 is turned on, the converter 9 including the transformer 91 is driven accordingly, and an AC signal is generated in each of the secondary windings n ₂₁ , n ₂₂ , and n ₁₂ . Each of these AC signals is rectified and smoothed, and after a certain period of time has passed since the power was turned on, each of them becomes a constant voltage due to the switching operation of the switch element Q1.

In the inrush current limiting circuit 8, the switch means SW is driven on when the output voltage E0 of the stabilizing circuit 4 reaches a constant value. When the switch means SW is turned on, the voltage EA (power) obtained in the capacitor C3 is supplied to the gate of the bidirectional switch 82 via the switch means SW, and the bidirectional switch 82 is turned on. As a result, the current from the power supply 1 is transferred to the bidirectional switch 82.
And the current limitation by the resistor 81 is released. At this point, the input capacitors 31 and 32 are already sufficiently charged, so that an excessive inrush current does not flow.

FIG. 2 is a structural connection diagram showing another embodiment of the present invention. In this embodiment, the inrush current limiting circuit 8 includes a transformer 84.

An AC signal (pulse voltage) obtained in the secondary winding n ₂₁ of the transformer 91 is input to the primary winding n ₈₁ of the transformer 84 via the switch SW, and is obtained in the secondary winding n _82. The AC signal is rectified and smoothed by the diode D3 and the capacitor C3, and the voltage EA obtained across the capacitor C3.
Is applied to the bidirectional switch 82.

Only when the switch SW is on, an output is generated on the secondary side of the transformer 84, a constant voltage is obtained across the capacitor C3, and this is given to the bidirectional switch 82 to be driven on. Therefore, by turning on the switch SW when the output voltage of the stabilizing circuit 4 reaches a constant value, it is possible to reliably prevent an excessive inrush current from flowing in.

In each of the above embodiments, the current limiting resistor 81 and the bidirectional switch 82 are connected in parallel, and this parallel circuit is connected in series with the rectifier circuit 2. Connect the directional switch 82 in series,
This series circuit may be connected in parallel with the rectifier circuit 2. In this case, the bidirectional switch 82 is turned on when the power is turned on and then turned off.

Further, the auxiliary power supply circuit 9 may be configured by a circuit other than the ringing choke converter.

(Effect of the Invention) As described above, according to the present invention, the bidirectional switch does not turn on before the input capacitor is sufficiently charged when the power is turned on, and an excessive inrush current is reliably prevented. be able to.

Further, in the present invention, the electric power obtained from the converter of the auxiliary power source is supplied to the secondary coil (n21) of the transformer of the converter via the switch means (SW) or the primary coil configured by a photocoupler via the switch means (SW). )
Is supplied to a bidirectional switch through a transformer (84) connected to the switch means (SW) to stabilize the circuit (4).
Since it is configured to be turned on when the output voltage E0 of the power supply reaches a constant value, it is possible to achieve cooperation with the stabilization circuit and to determine the type and capacity of the load connected to the output end of the stabilization circuit. Regardless, there is a special effect that an excessive inrush current can always be prevented with accurate timing.

[Brief description of drawings]

1 and 2 are configuration and connection diagrams showing an example of a circuit according to the present invention, and FIG. 3 is a configuration and connection diagram of a conventional circuit. 1 ... AC power supply, 2 ... Rectifier circuit, 31, 32 ... Input capacitor, 4 ... Stabilization circuit, 8 ... Inrush current limiting circuit, 81 ... Resistor, 82 ... Bidirectional switch, SW ...
... switch means, 9 ... auxiliary power supply, 91 ... transformer.

Claims (1)

[Scope of utility model registration request] 1. An alternating current power supply (1), a rectifier circuit (2) for converting alternating current from the alternating current power supply to a direct current, and a rectified output voltage obtained by the rectifier circuit, which is input to switch and stabilize the load. Circuit (4) for supplying electric power to the inrush current limiting circuit (8) comprising a parallel or series connection of a bidirectional switch and a current limiting resistor connected to a current circuit connecting an AC power supply and a rectifier circuit. And an auxiliary power supply (9) including a converter for inputting a rectified output voltage obtained by the rectification circuit and supplying electric power for operating the stabilization circuit, wherein the switching power supply device is obtained from the converter of the auxiliary power supply. The switch means (SW) or the primary side coil constituted by a photocoupler for electric power was connected to the secondary side coil (n21) of the transformer of the converter via the switch means (SW). Lance (8
4) is provided with circuit means for supplying to the bidirectional switch, and the switch means (SW) is turned on when the output voltage of the stabilizing circuit reaches a constant value. Inrush current limiting circuit for switching power supply.