JPH07231659A - Partial smoother circuit - Google Patents

Abstract

PURPOSE:To secure the safety of a power supply device while preventing the burning and dielectric breakdown of its partial smoother circuit. CONSTITUTION:In the partial smoother circuit of a power supply device which comprises capacitors C1, C2 and diodes D1, D2, D3, when an abnormal voltage is applied to C1 or C2, both Zener diode D4 and switching element Q1 are shorted via resistor R5 either by the actions of a transistor Q2, a resistor R3 and a Zener diode D5 or by the actions of a transistor Q3, the resistor R3 and a Zener diode D6. Thereby, the input current of the power supply device is increased, and a fuse on the power supply side of blown out.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a partial smoothing circuit for smoothing after rectifying an AC input voltage, which is safe because a device of the partial smoothing circuit is short-circuited or opened and the device burns or dielectric breakdown occurs. It is something that does not impair the sex.

[0002]

2. Description of the Related Art Here will be described what state a circuit becomes when a part of a partial smoothing circuit is short-circuited or opened.
FIG. 2 shows a switching power supply using a partial smoothing circuit which has been conventionally used. When the parts of the partial smoothing circuit are short-circuited or opened, the following phenomenon occurs. When either the capacitor C1 or the diode D3 is short-circuited, the voltage applied to the capacitor C2 becomes about twice the voltage at the normal time. When either the capacitor C2 or the diode D2 is short-circuited, the voltage applied to the capacitor C1 becomes about twice as high as the normal voltage. When the diode D2 is opened, the voltage applied to the capacitor C1 becomes higher than that in the normal state. The voltage is about 1.5 times, though it depends on the load. When the diode D3 is opened, the voltage applied to the capacitor C2 becomes higher than that in the normal state. Although the voltage varies depending on the load, it increases about 1.5 times.

[0003]

The problems of the conventional circuit will be described based on the above conditions. In the conventional partial smoothing circuit, when a component in the circuit is short-circuited or opened, a voltage higher than that in the normal state is applied to the capacitor C1 or the capacitor C2, and the capacitor is damaged because the rated voltage of the capacitor is exceeded. Since the capacitors used in the partial smoothing circuit are generally electrolytic capacitors, the explosion-proof valve operates, the electrolytic solution is scattered in a mist, and the insulation of the circuit is destroyed.
There is a serious risk of burning circuit components.

[0004]

The present invention has been made to solve the above-mentioned problems. When the applied voltage of the capacitor C1 or C2 exceeds the rated voltage as shown in FIG. Zener diode D5
Alternatively, since the Zener voltage of the Zener diode D6 is exceeded, the transistor Q2 or the transistors Q3 and Q2 are turned on, the Zener diode D4 and the switching element Q1 are short-circuited and broken, a short-circuit current flows in the circuit, and the input fuse F is blown to blow the input. This is intended to prevent the risk of insulation breakdown or burning of the device by cutting off the power supply and preventing the capacitor from being damaged.

That is, the first diode D1 is connected between the negative electrode (-) of the first capacitor C1 and the positive electrode (+) of the second capacitor C2 in the charging current flowing direction, and the first capacitor D1 is connected. The second diode D2 is connected between the negative electrode (−) of C1 and the negative electrode of the second capacitor C2 in the direction in which the discharge current of the capacitor C1 flows, and the positive electrode (+) of the first capacitor C1 and the second In the partial smoothing circuit in which the third diode D3 is connected between the positive electrode (+) of the capacitor C2 and the discharge current of the capacitor C2, between the positive electrode and the negative electrode of the first capacitor C1. A series circuit of the resistor R3 and the Zener diode D5 is connected with the anode of the Zener diode D5 on the negative side, and the Zener die is connected between the positive and negative electrodes of the second capacitor C2. A series circuit of a diode D6 and a resistor R4 is connected with the cathode of the Zener diode D6 on the positive side, and a resistor R3 is connected between the emitter and base of the PNP transistor Q2, and the emitter of the transistor Q2 is connected to the first capacitor C1. Of the transistor Q2 is connected to the cathode of the zener diode for starting the switching element Q1 via the resistor R5, and the resistor R4 is connected between the base and emitter of the NPN transistor Q3. , The emitter of the transistor Q3 is connected to the negative electrode (−) of the second capacitor C2, and the collector of the transistor Q3 is connected to the base of the transistor Q2.

[0006]

Since the present invention is constructed as described above,
When a voltage higher than the rated voltage is applied to the capacitor due to a fault in the circuit, the switching power supply element is short-circuited, the input fuse is blown, and the power supply to the power supply input is stopped. Burnout and dielectric breakdown can be prevented.

[0007]

FIG. 1 is a circuit diagram of an embodiment of the present invention,
The same parts as those in FIG. 2 are designated by the same reference numerals. In the figure, T
1 is a converter transformer, Q1 is a switching element (here, FET is shown), R1 and R2 are resistors, D4 is a zener diode, and a "control circuit" is a circuit for controlling the pulse width of Q1 of the switching power supply unit, C1 and C2. Is a capacitor of the partial smoothing circuit, D1, D2 and D3 are diodes of the partial smoothing circuit, D0 is a commercial diode for rectifying an AC input, F is a fuse, and the circuit of the present invention is formed by the following parts. D5 and D6 are Zener diodes, R3, R4 and R5 are resistors, Q2 is a PNP type transistor, and Q3 is an NPN type transistor.

The Zener diode D5 is connected in series with the resistor R3, is connected between the positive electrode (+) and the negative electrode (-) of the capacitor C1, and the resistor R3 is connected between the emitter and base of the transistor Q2. The transistor Q
2 emitter is connected to the positive electrode (+) of the capacitor C1,
The collector of the transistor Q2 via a resistor R5,
It is connected to the cathode of the Zener diode D4.
The Zener diode D6 is connected in series with the resistor R4, is connected between the positive electrode (+) and the negative electrode (−) of the capacitor C2, and the resistor R4 is connected between the base and emitter of the transistor Q3 to connect the capacitor C2. The emitter of the transistor Q3 is connected to the negative electrode (-),
Is a circuit in which the collector of is connected to the base of the transistor Q2.

In a normal state, the voltage V of the capacitors C1 and C2 of the partial smoothing circuit is approximately the voltage expressed by the following equation.

[0010]

[Equation 1]

Here, the capacitor C1 or the diode D
3 is destroyed and short-circuited, the voltage of the capacitor C2 is twice the normal voltage, that is, √2 × Vac (rm.
s. ) Will be applied. Similarly, when the capacitor C2 or the diode D2 is destroyed and short-circuited, the voltage of the capacitor C1 becomes twice the voltage at the normal time. In this way, when the capacitor C1 has an abnormal voltage,
A Zener current flows through the Zener diode D5, the voltage across the resistor R3 rises, the voltage between the base and emitter of the transistor Q2 rises, the transistor Q2 turns on, and the current flows through the resistor R5. Therefore, the Zener diode D4 is short-circuited. Break down the switching element Q1
In order to destroy the short circuit of the fuse, a large current flows to the input and the fuse F
By melting the capacitor C1, it is possible to prevent the capacitor C1 from breaking (valve operation) and prevent the dielectric breakdown due to the electrolytic solution.

When the capacitor C2 becomes an abnormal voltage, a Zener current flows through the Zener diode D6, the voltage across the resistor R4 rises, the voltage between the base and emitter of the transistor Q3 rises, and the transistor Q3 turns on. , The voltage across the resistor R3 rises, the base-emitter voltage of the transistor Q2 rises, the transistor Q2 turns on, and the current flows through the resistor R5. Therefore, the Zener diode D4 and the switching element Q1 are short-circuited by the above steps, and the fuse F can be blown to prevent the capacitor C2 from being destroyed, and the dielectric breakdown due to the electrolytic solution can be prevented.

[0013]

The partial smoothing circuit of the present invention has the effect of preventing circuit burnout and insulation breakdown and maintaining the safety of the power supply device.

[Brief description of drawings]

FIG. 1 is a partial smoothing circuit diagram of an embodiment of the present invention.

FIG. 2 is a conventional partial smoothing circuit diagram.

[Explanation of symbols]

 C1 1st capacitor C2 2nd capacitor D1 1st diode D2 2nd diode D3 3rd diode D0 Commercial diode D4 Zener diode for starting D5 Zener diode D6 Zener diode F fuse Q1 Switching element (FET or transistor) Q2 PNP type transistor Q3 NPN type transistor R1 resistor R2 resistor R3 resistor R4 resistor R5 resistor

Claims (1)

[Claims] 1. A first diode D1 is connected between a negative electrode (−) of a first capacitor C1 and a positive electrode (+) of a second capacitor C2 in a charging current flowing direction, and
Negative electrode (−) of the second capacitor C1 and the second capacitor C2
The second diode D2 is connected between the negative electrode (−) of the capacitor C1 and the negative electrode (−) in the direction in which the discharge current of the capacitor C1 flows,
Positive electrode (+) of the second capacitor C1 and the second capacitor C2
In the partial smoothing circuit in which the third diode D3 is connected between the positive electrode (+) and the positive electrode (+) of the first capacitor C2 in the flowing direction of the discharge current of the capacitor C2, the positive electrode (+) and the negative electrode (−) of the first capacitor C1 are connected. The Zener diode D5 connected in series with the resistor R3 between
Of the zener diode D6 connected in series with the resistor R4 between the positive electrode (+) and the negative electrode (−) of the second capacitor C2 with the anode of the capacitor C1 being the negative electrode (−) side. The cathode of the Zener diode D6 is connected with the positive electrode (+) side of the capacitor C2, and the resistor R3 is connected between the base and the emitter of the transistor Q2. The emitter of the transistor Q2 is the positive electrode (+) of the first capacitor C1. ), The collector of the transistor Q2 is connected to the switching element Q via the resistor R5.
1 is connected to the cathode of the Zener diode D4 for starting, and the resistor R4 is connected to the base of the transistor Q3.
A partial smoothing circuit connected between the emitters, the emitter of the transistor Q3 being connected to the negative electrode (−) of the second capacitor C2, and the collector of the transistor Q3 being connected to the base of the transistor Q2.