JPH0528069B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a switching regulator as a DC power supply device, and particularly to a switching regulator that suppresses inrush current to a smoothing capacitor using a transistor. It concerns Yureta.

[Background of the invention]

Up until now, methods for suppressing inrush current in this type of equipment have been shown in "Design Methods of Switching Regulators and How to Use Power Devices" (June 1980, published by Seibundo Shinkosha, pages 154 and 155). It is known that by connecting a resistor or a power thermistor before the smoothing capacitor, the inrush current flowing through the smoothing capacitor when the power is turned on can be suppressed. However, in the case of using a power thermistor, since the temperature drops slowly from the high temperature state, it cannot be expected to have a suppressing effect when the power source is turned on and off frequently. In addition, when using a resistor, a method is usually used to bypass the resistor using a thyristor, etc. during normal operation, but if the bypass element such as a thyristor cannot conduct for some reason, the resistor may generate abnormal heat. This may have an adverse effect on surrounding circuit elements.

By the way, taking the example of electronic switching equipment, the recent trend in DC power supplies is to use large-capacity DC power supplies with complex circuit configurations in order to ensure the reliability of the power supply for the entire switching system. The reality is that rather than centrally installing small-capacity DC power supplies, it has become mainstream to install small-capacity DC power supplies in a distributed manner within a switching system. Therefore, even though the circuit configuration of a small-capacity DC power supply device is simple, its reliability must be ensured.

[Purpose of the invention]

Therefore, an object of the present invention is to turn on the device more frequently,
Even when it is turned off, the inrush current can be suppressed well, and even if the current bypass element is not turned on for some reason, it has a simple circuit configuration that does not cause large abnormal heat generation. To provide a small capacity switching regulator.

[Summary of the invention]

For this purpose, the present invention is designed such that the inrush current that flows into the smoothing capacitor when the power is turned on is controlled by the voltage at the connection point of two resistors provided before the capacitor, and which divides the input DC power supply voltage. When applied as a bias voltage to the control input terminal, the voltage is applied to the control input terminal so as to be caused to flow through the transistor which is intended to operate in the active region.

[Embodiments of the invention]

The present invention will be explained below with reference to FIGS. 1 to 3.

First, the configuration of one embodiment of the switching regulator according to the present invention will be described. FIG. 1 shows its configuration. According to this, if AC100V power is applied to the input, the full-wave rectifier circuit
A full-wave rectified voltage is obtained from REC, but the full-wave rectified voltage is divided by resistors R1 and R2, and a forward bias voltage is applied between the base and emitter of transistor Q1. As a result, a base current I _B is caused to flow through the transistor Q1.
A collector current I _C corresponding to h _FE ·I _B (h _FE ; forward current amplification factor) flows into the capacitor C1 as a charging current. Now, when capacitor C1 is charged to a certain voltage value, the auxiliary power supply circuit (not shown) starts operating and the pulse width control circuit
Since power is supplied to the PWMC, the main transistor Q2 starts a switching operation. Power is supplied via the transformer T to the output side consisting of the diode D2 and the capacitor C2 by the switching operation of the main transistor Q2.

On the other hand, the output voltage should be a constant voltage, so that the voltage value is the reference voltage from the reference power supply E and the comparator.
It has become a constant comparison in CMP. As a result of controlling the on-state pulse width of the main transistor Q2 by the comparison output of the comparator CMP, the output voltage is maintained at a constant value.

By the way, in this example, the transistor Q1 is bypassed by the thyristor TH, so that almost no current flows through the transistor Q1 except at the initial stage when the power is turned on. By switching main transistor Q2, diode D1 and resistor R
A gate trigger voltage is applied to the thyristor TH through a gate trigger circuit consisting of 3 and R4, and the thyristor TH is placed in a conductive state. Due to this conduction state, transistor Q1
is bypassed, so the thyristor is
Current flows through TH, and almost no current flows through transistor Q1. Let's talk about the case where the thyristor TH fails and does not conduct even after the main transistor Q2 starts switching. In such a field, all the current to the capacitor C1 and the transformer T flows through the transistor Q1, and the transistor Q1 will generate heat. However, if the transistor Q1 is attached to a heatsink made of aluminum or the like, it can sufficiently withstand the heat generated, and even if it cannot withstand the heat generated, it is possible to attach a temperature fuse or the like to the heatsink. , it becomes possible to turn off the power before the transistor Q1 is destroyed.

Next, another embodiment that takes into consideration the case where the output power is small will be described. FIG. 2 shows its configuration. As shown in the figure, the thyristor and gate trigger circuit are removed from the configuration shown in Figure 1, and the capacitor C is always connected via the transistor Q1.
1 and the transformer T. This is because the current flowing through the transistor Q1 is small during steady state, and the transistor Q1 can be used in the saturation region, and the loss of the transistor Q1 can be suppressed to a small value.

It is clear that in the configurations shown in FIGS. 1 and 2, inrush current can be suppressed even if the power source is turned on and off frequently. Further, although the above description has been made of a device having a DC-DC converting transformer, it is also applicable to a device having a chiyoke coil CH and a flywheel diode D3, as the basic configuration is shown in FIG.

〔Effect of the invention〕

As explained above, in the present invention, the inrush current to the capacitor is passed through the transistor, so the power supply is turned on frequently.
Inrush current can be suppressed even when turned off,
Even if the added bypass element cannot conduct, there is an effect that no abnormal heat generation occurs.

[Brief explanation of the drawing]

FIG. 1, FIG. 2, and FIG. 3 are diagrams each showing the configuration of an embodiment of a switching regulator according to the present invention. REC...Full wave rectifier circuit, R1, R2...Resistance,
Q1...transistor, C1...(smoothing) capacitor, Q2...main transistor, PWMC...pulse width control circuit.

Claims (1)

[Claims] 1. In a switching regulator having a smoothing capacitor for smoothing DC input,
When the power is turned on, the inrush current that flows into the smoothing capacitor is applied to the control input terminal as the control input bias voltage at the connection point of two resistors that are provided before the capacitor and divide the input DC power supply voltage. A switching regulator characterized by a configuration in which the current flows through a transistor designed to operate in the active region.