JP3049108B2 - Switching type DC stabilized power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching type stabilized DC power supply.

[0002]

2. Description of the Related Art FIGS. 1 and 2 are a conventional circuit diagram of this kind and operation waveform diagrams of respective parts. In FIG. 1, Vin is an AC input (voltage) and D1 is a rectifying bridge, thereby forming a DC power source E. I do. R1 and SCR are resistors and thyristors connected in parallel, and are connected between the DC power supply E and the input capacitor C1 to prevent an inrush current of the capacitor C1. Next, T1 is an output transformer, the primary winding n1 of which is connected in series with the switch element (transistor) Q1 and connected to both ends (DC output terminals) of the capacitor C1. ns is an auxiliary winding of the transformer T1, one end of which is connected to one terminal of the primary winding n1 and the other end of which is a diode D2.
The thyristor S is connected via a capacitor C2 and a resistor R2.
The thyristor SCR1 is connected to the gate of CR1 to form a gate circuit of the thyristor SCR1. n2 is a secondary (output) winding;
D3 and D4 are output rectifying diodes; L1 and C3 are choke coils and capacitors forming an output smoothing circuit;
Applies a pulse signal whose pulse width is controlled by the switching control circuit of the transistor Q1 according to the output voltage E0 to the transistor Q1.

The operation of this circuit is based on an AC input Vin (FIG. 2).
When a) is applied, a DC voltage E is generated through the rectifying diode D1, and the inrush current is prevented by the resistor R1, and the capacitor C1 is charged while being limited by the resistor R1, as shown in FIG. The charging voltage increases.
When the charged pressure reaches a predetermined value, the transistor Q1 starts the switching operation via the control circuit A. At the same time, the voltage of the auxiliary winding ns causes the diode D
2. A gate signal is sent to the thyristor SCR1 via the resistor R2, and this is turned on (ON).
One end is short-circuited by the thyristor SCR1.
On the secondary winding n2 side, DC is supplied through rectifier diodes D3 and D4 and smoothing circuits L1 and C3. The control circuit A supplies a stabilized DC E0 via a rectifying diode and a smoothing circuit to supply a pulse signal to the transistor Q1 according to the output voltage E0.

[0004]

In the above-mentioned conventional circuit, when a momentary interruption occurs in the AC input Vin at time t2 shown in FIG. 2, the capacitor C1 starts discharging. Then, when the voltage drops to a voltage that is the operable limit of the switching regulator and is restored at time t3, in the above state, the thyristor SCR1 receives a gate signal through the auxiliary winding ns and is in a normal conduction state. As shown in FIG. 2C, an excessive current flows through the capacitor C1 due to the restoration of power, so that the capacitor C1 is deteriorated, and there are problems such as shortening the life. Further, since the auxiliary winding ns is provided in the output transformer T1 to supply the gate signal of the thyristor, there is a disadvantage that the size of the transformer T1 is increased.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a stabilized DC power supply provided with an inrush prevention circuit for preventing an inrush current at the moment of an instantaneous input interruption and simplifying a gate circuit.

[0006]

FIGS. 3 and 4 are circuit diagrams of one embodiment of the present invention and operation waveform diagrams of respective parts thereof. The main component of the present invention is that in the inrush current prevention circuit B, a parallel circuit of a voltage driving element (FET) and a resistor (R1) is provided between a DC power supply (E1) and a capacitor (C1), and the voltage driving element (FET) is provided. ), And a bypass circuit for opening the gate circuit by detecting a voltage drop due to the current flowing through the parallel circuit is provided to turn off the voltage driving element. Incidentally, the gate circuit is configured by connecting a connection point a of the resistor R3 and the constant voltage diode DZ1 connected between the DC power supplies to the gate of the FET (field effect transistor). Further, the bypass circuit includes a voltage driving element (FE
T) A collector and an emitter are connected between one end a of the gate circuit and one end b on the DC power supply side of the parallel circuit, and a base is connected to one end c of the parallel circuit on the capacitor side via a constant voltage element DZ2. It is composed of a transistor Q2.

The main circuit operation of the circuit of the present invention is basically the same as that of the conventional example. The operation of the inrush current prevention circuit B will be described. When the input voltage Vin is applied at time t = t1 in FIG. 4, a voltage is applied to the gate of the FET by R3 and DZ1 and the FET is once conducted. When an inrush current flows for charging, the combined resistance of R4 and the series resistor (R1) connected in parallel with the ON resistance of the series FET (R1)
When the voltage drop across X) exceeds the Zener voltage of DZ2, Q2 conducts and turns off the FET. Thereafter, C1 is charged by the current limited by R1, C1 is sufficiently charged, and the voltage drop at R1 becomes DZ
When the voltage becomes equal to or lower than 2, the FET conducts, and a normal current flows.
In other words, the inrush current changes the Zener voltage of DZ2 to the above RX
Current limit. The principle of limiting the inrush current in the present invention is the same as in the case of return after momentary input interruption. At time t = t2, an instantaneous interruption of the input occurs, and when returning at t3, the rush current for charging C1 flows because the voltage of VC1 has dropped. When the voltage is exceeded, the FET is turned off,
Current is limited. Thereafter, C1 is charged by R1, and R1 is charged.
When the voltage drop of 1 becomes equal to or less than DZ2, the FET conducts, and a normal current flows. In this circuit, if the inrush current can be detected by the ON resistance of the FET, the resistor R4 is unnecessary.

[0008]

According to the present invention, an excessive inrush current can be prevented even when the input is momentarily interrupted and the power is restored as shown in FIG. 4D, and it is necessary to provide an auxiliary winding in the transformer. There is no. Therefore, the circuit configuration is simple and the capacitor C
1. Practical effects are large, such as prevention of breakage of the rectifying diode D1 and an input fuse (not shown).

[Brief description of the drawings]

FIG. 1 is a conventional circuit diagram

FIG. 2 is an operation waveform diagram of each part of the conventional circuit.

FIG. 3 is a circuit diagram of one embodiment of the present invention.

FIG. 4 is an operation waveform diagram of each part of the circuit of the present invention. D1 Rectifier bridge diode B Inrush current prevention circuit C1 Input capacitor T Output transformer Q1 Switch element (transistor) FET Field effect transistor (voltage drive element)

Continued on the front page (51) Int.Cl. ⁷ Identification code FI H02M 3/28 H02M 3/28 C

Claims (2)

(57) [Claims] A first capacitor connected between a DC power supply and an output terminal of the DC power supply; a primary winding of an output transformer and a switching element connected in series between terminals of the smoothing capacitor; A conversion output is supplied to the secondary winding side of the output transformer using the switching operation of the element, and a parallel circuit of a voltage driving element and a resistor is provided between one end of the DC power supply and one end of the smoothing capacitor. A switching type stabilized DC power supply configured to limit an inrush current of the smoothing capacitor via the parallel circuit, wherein a gate circuit of the voltage driving element is provided and a bypass circuit for releasing the gate circuit is provided; and In the bypass circuit, an emitter and a collector are connected between one end a of the gate circuit and one end b of the parallel circuit on the DC power supply side, and the base is a constant current source. A transistor connected to one end of a smoothing capacitor of the parallel circuit via an element, wherein a voltage drop across the combined resistor of the parallel circuit is directly detected by the constant voltage element, and the detected voltage is detected by the constant voltage element. Wherein the voltage driving element is turned off via the bypass circuit when the Zener voltage of the switching type is reached. 2. A gate circuit comprising a resistor and a constant voltage diode connected in series between a DC power supply, and a connection point between the resistor and the constant voltage diode connected to a gate of a voltage driving element. The switching type stabilized DC power supply according to claim (1).