JPH04340364A - Switching regulator - Google Patents

Abstract

PURPOSE:To suppress a rush current applied to a switching device with a simple and low cost construction by a method wherein a varistor is connected in parallel with a reactance element in a resonance circuit. CONSTITUTION:A varistor 73 is connected in parallel with a capacitor 72 in a resonance circuit 7. A voltage between both the terminals of the capacitor 72 is gradually increased in accordance with the increase of a maximum current i1 flowing through a route composed of a transistor 61, the capacitor 72, a primary winding 71 and a transistor 64. If the voltage between both the terminals of the capacitor 72 reaches a varistor voltage, a current is applied to the varistor 73 and the voltage between both the terminals of the capacitor 72 is limited. With this constitution, a rush current applied to a switching device can be suppressed with a low cost and simple construction.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching regulator, which is a type of stabilized power supply circuit.

0002

2. Description of the Related Art FIG. 6 shows an example of a conventional switching regulator. The alternating current voltage is exchanged into direct current by the rectifier circuit 2 and smoothed by the capacitor 4. Then, the DC voltage across the capacitor 4 is converted into an AC voltage by the switching circuit 6. The switching circuit 6 includes four full-bridge connected switching elements, transistors 61, 62, 63 and 64, transistors 61 and 64, and transistors 62 and 6.
3 and a drive circuit 65 that turns on and off alternately. A resonant circuit 7 consisting of a transformer 70 and a capacitor 72 connected in series to a primary winding 71 of the transformer 70 is provided at the next stage of the switching circuit 6 . The output AC voltage of the resonant circuit 7 is applied to the secondary winding 7 of the transformer 70.
The rectifier circuit 7 and the capacitor 9 connected to the DC current are converted into direct current and smoothed.

A diode 9 is connected across the capacitor 72.
1, a capacitor 92 and a resistor 93 are connected, and a diode 94, a capacitor 95 and a resistor 96 are also connected. Diodes 91 and 94, capacitor 9
2 and 95 and resistors 93 and 96 suppress the voltage applied across the capacitor 71 and reduce the rush current flowing through the path of the transistor 63, the primary winding 71, the capacitor 72, and the transistor 62, and the transistor 61, the capacitor 72, and the primary It is provided to reduce the rush current flowing through the path of the winding 71 and the transistor 64.

FIG. 7 shows another example of a conventional switching regulator. Components in FIG. 7 that are the same as those in FIG. 6 are given the same reference numerals. however,
The switching circuit 6 includes half-bridge connected transistors 66 and 67, and these transistors 66.
and a drive circuit 68 that turns 67 on and off alternately.

[0005]

The conventional switching regulator shown in FIG. 6 and FIG.
1 (and 94), a capacitor 92 (and 95), and a resistor 93 (and 96), resulting in a large number of components and high cost.

The present invention has been made to solve these problems, and an object of the present invention is to provide a switching regulator that has a simple and low-cost configuration and can suppress rush current flowing through a switching element.

[0007]

[Means for Solving the Problems] A switching regulator according to claim 1 is a switching regulator having a switching element and a resonant circuit provided in a current path passing through the switching element, wherein the reactance of the resonant circuit is It is characterized by a varistor connected to the element in parallel.

A switching regulator according to a second aspect of the present invention is characterized in that the reactance element is a capacitor.

A switching regulator according to a third aspect of the present invention is characterized in that a switch is provided in a current path.

0010

In the switching regulator according to the first aspect, when the voltage across the reactance element reaches the varistor voltage, current flows through the varistor and the voltage across the reactance element is limited. This suppresses the rush current flowing through the switching element.

In the switching regulator according to the second aspect of the invention, when the voltage across the capacitor reaches the varistor voltage, current flows through the varistor and the voltage across the capacitor is limited. This suppresses the rush current flowing through the switching element. The voltage across the capacitor in the resonant circuit is the coil (inductance element) in the resonant circuit.
Since the voltage across the capacitor is smaller than the voltage across the capacitor, the withstand voltage of the varistor can be small if the varistor is connected in parallel to the capacitor.

In the switching regulator according to claim 3, there is a possibility that a larger current flows when the switch is turned on and off than when no switch is provided in the switching element, but the voltage across the reactance element (capacitor) reaches the varistor voltage. Current then flows through the varistor, limiting the voltage across the reactance element. Therefore, rush current flowing through the switching element is suppressed.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the configuration of an embodiment of a switching regulator according to the present invention. Among the components of FIG. 1, the same components as those of the conventional switching regulator of FIG. 6 are given the same reference numerals. A feature of this embodiment is that a varistor 73 is connected in parallel to the capacitor 72 of the resonant circuit 7.

If the output AC voltage and angular frequency of the switching circuit 6 are e and w, the leakage inductance of the primary winding 71 of the transformer 70 is L1, and the capacitance of the capacitor 72 is C1, then the transistor 61 and the capacitor 72 are
, the maximum current flowing through the path of the primary winding 71 and the transistor 64 (or the current flowing through the path of the transistor 63, the primary winding 71, the capacitor 72, and the transistor 62) i1 is the AC voltage as shown by the following equation 2. e1
is divided by the series resonant impedance Z1 (Equation 1) of the leakage inductance L1 and the capacitance C1.

[Math 1]

[Math 2]

The voltage across the capacitor 72 is i1/wC1
and gradually increases as i1 increases. When the voltage across the capacitor 72 reaches the varistor voltage, current flows through the varistor 73 and limits the voltage across the capacitor 73. This is equivalent to increasing C1 of 1/wC1. Therefore, 1/wC1 becomes smaller and Z
1 becomes larger. Therefore, as is clear from Equation 2, the current i1 is suppressed. According to experiments, when the varistor 73 was not provided, i1 increased to 15A, but when the varistor 73 was provided, i1 could be suppressed to 8A or less.

FIG. 2 shows another embodiment of the switching regulator of the present invention. In this experimental example, the rectifier circuit 8 and smoothing capacitor in Figure 1 are connected to the main current (set power supply).
100, another resonant circuit consisting of a transformer 70S and a capacitor 72 is provided in parallel with the switching circuit 6, and the rectifier circuit 8S and smoothing capacitor 9S connected to the secondary winding 74S of the transformer 70S are connected to a standby power supply ( (remote control power supply) 200. A switch SW1, which is an electromagnetic switch or a mechanical switch, is provided between the switching circuit 6 and the primary winding 71 of the transformer 70.

The standby power supply 200 is always in operation, and the main power supply 100 is activated when the switch SW1 is turned on.

FIG. 3 shows an equivalent circuit of the embodiment of FIG. In this equivalent circuit, the switching circuit 6 is shown as an AC power supply e. When the switch SW1 is turned on, the charging current of the capacitance Cθ of the smoothing capacitor 9 and the current flowing through the load resistance RL of the main power supply 100 flow into the secondary winding 74 of the transformer 70. As a result, whether current flows through the primary winding 71 or its maximum current i1 can be expressed by the above-mentioned equation 2. The inductance of the primary winding 71 is large when the switch SW1 is on, and gradually decreases as current flows through the secondary winding 74. For this reason,
The current i1 gradually increases. When the voltage across the capacitor 72 reaches the varistor voltage, a current flows through the varistor 73, the voltage across the capacitor 72 is limited, and the current i1 is suppressed as in the embodiment of FIG. According to experiments,
In the case where the varistor 73 is not provided in FIG.
1 increased to 25A, but when the varistor 73 was provided, i1 could be suppressed to 8A or less.

FIG. 4 shows a third embodiment of the switching regulator of the present invention. In this embodiment, transistors 66 and 67 of the switching circuit 6 are push-pull connected and are turned on and off alternately by a drive circuit 68, and two capacitors 75 and 77 are connected to the resonant circuit 7, and these capacitors are connected in parallel. The only difference from the embodiment of FIG. 2 is that varistors 76 and 78 are connected to the varistors 76 and 78, and the operation is similar to that of the embodiment of FIG.

FIG. 5 shows a fourth embodiment of the switching regulator of the present invention. This embodiment differs from the embodiment in FIG. 1 only in that the transistors 66 and 67 of the switching circuit 6 are half-bridge connected and are turned on and off alternately by the drive circuit 68, and the operation is the same as in the embodiment in FIG. be.

In the above embodiment, the varistor is connected in parallel to the capacitor 72 of the resonant circuit, but the varistor may be connected in parallel to the primary winding 71 of the resonant circuit. However, it is preferable to connect a varistor in parallel to the capacitor 72 because the withstand voltage of the varistor can be reduced by connecting the varistor in parallel to the capacitor 72.

[0022]

As described above, according to the switching regulator according to claim 1, since the varistor is connected in parallel to the reactance element of the resonant circuit, when both ends of the reactance element reach the varistor voltage, the current flows through the varistor. flows and the voltage across the reactance element is limited, so the rush current flowing through the switching element can be suppressed at low cost and in a simple manner.

According to the switching regulator according to the second aspect, since the reactance element to which the varistor is connected is a capacitor, the withstand voltage of the varistor can be reduced.

According to the switching regulator according to claim 3, a switch is provided in the current path of the resonant circuit, and even if this switch is turned on or off, the varistor is provided in parallel with the reactance element (capacitor) of the resonant circuit. , rush current flowing through the switching element can be suppressed.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the configuration of a first embodiment of the switching regulator of the present invention.

FIG. 2 is a circuit diagram showing the configuration of a second embodiment of the switching regulator of the present invention.

[Figure 3] A circuit diagram showing an equivalent circuit of the embodiment in Figure 2.

[Figure 4]
A circuit diagram showing the configuration of a third embodiment of the switching regulator of the present invention

FIG. 5 is a circuit diagram showing the configuration of a fourth embodiment of the switching regulator of the present invention.

[Figure 6] Circuit diagram showing an example of a conventional switching regulator

[Figure 7] Circuit diagram showing another example of a conventional switching regulator

[Explanation of symbols]

6 Switching circuit 7 Resonant circuit 61, 62, 63, 64, 66, 67 Transistor 65, 68 Drive circuit 70 Transformer 72, 75, 77 Capacitor 73, 76, 78 Varistor

Claims (3)

[Claims] 1. A switching regulator comprising a switching element and a resonant circuit provided in a current path passing through the switching element, characterized in that a varistor is connected in parallel to a reactance element of the resonant circuit. regulator. 2. The switching regulator according to claim 1, wherein the reactance element is a capacitor. 3. The switching regulator according to claim 1, wherein a switch is provided in the current path.