JPS62123918A - Rush-current control circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Summary] In a switching regulator equipped with an inrush current control circuit composed of an inrush current limiting resistor and a switching element connected in parallel to both ends of the resistor and turned on when power supply starts, a snubber circuit is provided. Provided is an inrush current control circuit provided with means for supplying a voltage induced in the switching element as a driving voltage of the switching element.

[Industrial application field]

The present invention relates to improvements in rush current control circuits in switching regulators and the like.

In recent years, switching regulators have been widely used as power sources for electronic devices.

A large-capacity rectifying capacitor is used in the rectifier circuit that supplies DC voltage to the switching regulator, and the switching regulator is set to operate when the voltage rises above a predetermined voltage.

An inrush current prevention circuit is provided to prevent this.

However, conventional inrush current control circuits are expensive and have operational problems, so a simple inrush current control circuit is desired.

[Conventional technology]

Fig. 3(a) shows a block diagram of a switching regulator equipped with a conventional AC rectifier circuit and an inrush current control circuit, Fig. 3('b) is an explanatory diagram of the operation when the power is turned on, and Fig. 3(C) shows the details of each part. The operation will be explained with reference to waveform diagrams.

Figure 3 (al) shows a switching regulator in which the switching transistor TRI is switched by an external input at a frequency of several tens of KH2, and is converted to a predetermined DC voltage by a switching transformer T. It is composed of a diode bridge DB and a rectifying capacitor C1. In the figure, a resistor R2, a capacitor C2, and a diode D2 constitute a well-known snubber circuit, and an auxiliary coil T1, a diode D3 .
Resistors R3, R4, capacitor C3, thyristor G1, and resistor R1 constitute an inrush current control circuit.

The inrush current control operation will be explained below.

When the power is turned on, the thyristor Gl is off, and the capacitor C1, which has a large capacity, is charged through the resistor R1. Therefore, the maximum value of the inrush current is limited by this resistor R1, and as shown in FIG. 3(b), the inrush current decreases due to the time constant CIRI, and the voltage Vc of 01 increases.

When Vc reaches a predetermined voltage, a drive pulse is input to TRI, and the switching regulator starts operating. At the same time, a pulse induced in the auxiliary coil TI makes the thyristor G1 conductive and supplies power to the load.

As described above, the inrush current is limited by the resistor R1, and the thyristor G1 is turned on at the start of switching to supply power.

The operation of the snubber circuit will be explained with reference to FIG. 3(C).

Figure 3 (c+ -(1) is the switching transistor T
The current waveform of R1 (2) is the voltage Vce across TR1.

Since switching is performed using the switching transformer T as a load, when the TRI is turned off, a high voltage Vp is generated as shown by the dotted line in the figure.

A spanner circuit is provided to prevent the TRI from being destroyed due to the generation of this high voltage Vp, and when Vp>Vc, the capacitor C2 is connected to Vpl through the diode D2.
When Vce becomes lower than Vp', 02 is discharged through resistor R2. (Figure 3(C) - Therefore, R2
, C2, Vpl can be set below the withstand voltage of TR~C1. Figure 3(c)-(2)
This shows a state in which RV ce is clamped at Vpl.

The rush current control circuit described above is expensive because it requires the auxiliary coil T1, and a simple method is to use the third current voltage and make the thyristor G1 conductive by a time constant circuit (R5, C4, etc.).

For this reason, there are problems such as not being able to synchronize with the switching operation, or only operating when the power is initially turned on, and therefore inrush current that occurs when the switching operation is stopped and restarted while the Ie is turned on cannot be prevented. be.

[Problem that the invention seeks to solve]

As explained above, the conventional inrush current control circuit provided with an auxiliary coil becomes a cost amplifier, and the method using the Z DC voltage that is obtained due to the auxiliary coil has operational problems.

Therefore, an object of the present invention is to provide a simple inrush current control circuit in a switching regulator.

[Means for solving problems]

For the above purpose, the inrush current control circuit of the present invention is provided with means (2) for driving the inrush current control switch element by the voltage generated in the snubber circuit (1), as shown in the principle explanatory diagram in FIG. It is something.

[Effect]

That is, a voltage is generated across the resistor R2 of the snubber circuit due to the above-mentioned high voltage at the start of the switching operation, and by supplying this voltage to the gate of the thyristor G1, the thyristor G1 can be made conductive. can.

〔Example〕

The details of the present invention will be explained according to the embodiment shown in FIG.

The inrush current control circuit of the present invention is composed of a thyristor G1 and a limiting resistor R1 connected in parallel, and a circuit that drives the thyristor G1 by the voltage of the snubber circuit 1, as shown in FIG. Diode D2, resistors R6, R7 and capacitor C5
constitutes the snubber circuit 1, and resistors R8 and R9 constitute a circuit that divides the voltage generated in the snubber circuit 1 (voltage at point A) and supplies it to the gate of the thyristor G1.

The voltage flows to the capacitor CI, and the voltage increases.

When a predetermined voltage is reached, a driving pulse is supplied to TRI, and TR
I starts a switching operation.

The snubber circuit 1 operates to clamp Vce, and a voltage is supplied to the gate of the thyristor G1 through the resistors R6 and R7, making the thyristor G1 conductive and supplying power to the load.

The above operation provides an inrush current control circuit in which the thyristor Gl becomes conductive based on the switching operation.

In the circuit shown in Figure 2, R7 changes the voltage at point A to R8 and R9.
C6 is a capacitor for noise prevention.

In order to supply the drive voltage from the snubber circuit as described above,
A simple circuit consisting of a resistor and a capacitor can provide the same functionality as a conventional auxiliary coil.

Note that the thyristor G1 can be replaced with another switching element, and the present invention is not limited to the thyristor.

〔Effect of the invention〕

As explained above, the present invention provides a simple circuit that drives a switching element for inrush current control using the voltage generated in the snubber circuit, and the cost reduction effect by reducing the auxiliary coil of the switching transformer is significant. be.

[Brief explanation of drawings]

Fig. 1 is a diagram explaining the principle of the present invention, Fig. 2 is a block diagram of a switching regulator according to an embodiment, Fig. 3 (al is a block diagram of a conventional switching regulator, Fig. 3 is an explanation of the operation when the power is turned on) Figure, Figure 3 TCI
are waveform diagrams of each part, and Figure 3 (dl is a block diagram of another conventional switching regulator). In the figure, l is a snubber circuit, 2 is a drive circuit, R1 is a limiting resistor, and R2 is a snubber circuit. Constituent resistors: R3 and R4 are thyristor driving resistors using an auxiliary coil, R6 and R7 are resistors for the snubber circuit of the embodiment, R8 and R9 are voltage dividing resistors, C1 is a rectifier capacitor, and C2 and C5 are the snubber circuit. capacitor, C3,
C6 is a noise prevention capacitor, 1FZ, D2 is a diode that constitutes a snubber circuit, DB is a diode block, G1 is a thyrisk, T is a switching transformer, TI is an auxiliary coil, and TRI is a transistor. Agent Patent Attorney Igeta Point - (' ・□++: %1 Drawing) Color Example
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Waveform Figure 35

Claims (1)

[Scope of Claims] An inrush current control circuit in a switching regulator comprising a rectifier circuit that rectifies an alternating current voltage and a snubber circuit that prevents high voltage generated by a switching transformer, the inrush current control circuit comprising: a rectifier capacitor (C1) of the rectifier circuit; The snubber circuit includes a resistor (R1) that is inserted in series with the resistor (R1) to limit inrush current when an AC voltage is applied, and a switch element (G1) that is connected in parallel to the resistor and becomes conductive when the switching regulator starts operating. An inrush current control circuit characterized by comprising means (2) for driving the switching element with the voltage generated in (1).