JPS6181176A - Overvoltage protecting circuit of ringing choke converter - 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 [Field of Industrial Application] The present invention relates to overvoltage protection for a ringing choke type DC-DC converter, and more specifically, when an overvoltage is detected, the secondary The present invention relates to an overvoltage protection circuit for a ringing choke converter that stops the oscillation operation of the converter by short-circuiting the side output windings.

[Prior art] A ringing peak converter is a type of automatic single switching regulator that uses blocking oscillation.It has the advantage of having a small number of parts and is widely used in power supplies with small output capacity. .

However, when the power supply input voltage rises abnormally, or when a failure occurs in each main part of the constant voltage power supply and the constant voltage control circuit stops functioning, the output voltage jumps. Incidentally, in the case of a power supply of about 12V-2A, the voltage is 3 in an uncontrolled state.
It reaches 0-40V. When such an overvoltage condition occurs, problems such as damage to the output smoothing capacitor, abnormal heating of the switching transistor, resistor, etc., and damage to the load occur. In particular, since a large capacity capacitor for output smoothing is filled with a liquid electrolyte material such as ethylene glycol, there is a risk that the capacitor may become punctured and burnt out, causing a major accident. Therefore, if an overvoltage occurs, it is necessary to detect it and immediately cut off the output.

For this purpose, an overvoltage protection circuit is incorporated.

A conventional overvoltage protection circuit is configured as shown in FIG. 2, for example. In the figure, a portion surrounded by a broken line and designated by the reference numeral 11 is a conventional overvoltage protection circuit. That is,
A detection winding Nl is provided in the transformer T, and its output is rectified by a diode D1, and the peak and output voltage is rectified by a capacitor C1.
It is charged and its output is applied to a Zener diode ZD for overvoltage detection. On the other hand, the primary input section of the converter includes a resistor R2, a thyristor SCR,1, and a resistor R3.
The terminal voltage of the resistor R0 is applied to the base of the overvoltage protection transistor Q2 connected between the base and emitter of the oscillation switching transistor Q. The current of the Zener diode ZD for overvoltage detection is supplied as a trigger current to the gate of the thyristor SCR.

While the converter is operating normally, the thyristor SC
Both Ri and overvoltage protection transistor Q2 are in an off state. However, if an overvoltage condition occurs for some reason, an abnormally high voltage will be induced in the detection winding N.
Capacitor C1 is charged. Then, the overvoltage detection Zener diode ZD becomes conductive, thereby causing the thyristor SCR1 to fire and become conductive. Therefore, a current flows through the resistor R0, a voltage drop occurs, and the terminal voltage is applied to the base of the overvoltage protection transistor Q2. As a result, the overvoltage protection transistor Q2 becomes conductive.
This lowers the base potential of the switching transistor Q1 of the converter and stops its oscillation operation.

[Problems to be solved by the invention] However, with this configuration, the converter body has a simple configuration with a small number of parts, while
The overvoltage protection circuit includes resistors a1 to R1, Cyrisk SCR
The number of components such as the overvoltage protection transistor Q, the Zener diode ZD for overvoltage detection, the diode D□, the capacitor C1, and the transformer detection winding 11N is significantly increased, which is a major factor in increasing costs.

Furthermore, since the number of parts is large and the circuit is complicated, assembly is troublesome and reliability is reduced.

The object of the present invention is to overcome the above-mentioned drawbacks of the prior art, and to provide an improved ringing circuit which has an extremely small number of parts and a circuit element, which is therefore highly reliable, easy to assemble, and can be miniaturized. 7. An object of the present invention is to provide an overvoltage protection circuit for a power converter.

[Means for Solving the Problems] The present invention, which can achieve the above objects, includes a thyristor inserted between the secondary output windings of a ringing reed converter, and a secondary rectification smoothing system. an overvoltage detection element is connected between the output of the thyristor and the gate of the thyristor;
igniting a thyristor by the overvoltage detection element when overvoltage is detected, and short-circuiting the secondary output windings of the transformer with the thyristor during the conduction period of the switching transistor;
This is an overvoltage protection circuit for a ringing check converter that stops the self-excited oscillation operation of the converter.

Secondary 1lII here! The overvoltage detection element connected between the first-stream smoothed output and the gate of the thyristor includes:
Usually, a Zener diode is used that has a certain constant voltage characteristic such that it becomes conductive when there is an overvoltage. It is also desirable to insert a diode in series with the thyristor to protect the thyristor from reverse voltage.

[Function] With such a configuration, if constant voltage control becomes impossible for some reason and an overvoltage occurs at the output, the overvoltage detection element, such as a Zener diode, becomes conductive, which causes a trigger current to flow through the thyristor. conduction. As a result, the energy that would have been stored in the transformer during the conduction period of the switching transistor is reduced to W due to the short circuit between its secondary output windings.
Since it is immediately released without being accumulated, the switching transistor stops its self-oscillation operation and remains in that state. This operation cuts off the output voltage, making it possible not only to protect the load but also to prevent damage to the Humbater itself.

[Example] The present invention will be explained in more detail below based on the drawings. FIG. 1 is a circuit diagram showing an embodiment of a ringing check converter incorporating an overvoltage protection circuit according to the present invention. The structure and operation of the ringing fault converter itself are exactly the same as those conventionally known. transformer T
Using the induced voltage in the feedback winding P2, the switching transistor Q is turned on and off to convert the positional current into alternating current,
The voltage is converted by the collector winding P and the secondary output winding Sl, and the output is rectified and smoothed by the rectifier diode D and the smoothing capacitor C. To stabilize the output voltage,
For example, this can be done by providing an rtIJ Mitsuki transistor Q3 between the base and emitter of the switching transistor Q1 and applying a control signal to the base of the #-registered transistor Q3.

Now, in FIG. 1, the part surrounded by the broken line is the overvoltage protection circuit 1 according to the present invention. As is clear from this circuit diagram, the overvoltage protection circuit 1 according to the present invention includes a series connection of a diode D2 and a thyristor SCR inserted between both terminals of the secondary output winding S of a ringing check converter. At the same time, a Zener diode ZD is connected as an overvoltage detection element between the output of the secondary rectifier diode D and the gate terminal of the thyristor SCR, and the thyristor S
This configuration has a resistor R connected between the gate and cathode terminals of CR.

This overvoltage protection circuit operates as follows.

Now, suppose that for some reason the constant voltage operation of the ringing torque converter becomes uncontrollable and the output voltage increases. When the increased output voltage exceeds a preset voltage value as an overvoltage, the Zener diode ZD becomes conductive, thereby firing the thyristor SCR and making it conductive.

Then, the secondary output winding S1 of the transformer T becomes the thyristor S.
They are short-circuited in the forward direction through CR and diode D2. As a result, during the conduction period of the switching transistor Q, the energy that should be stored in the transformer T is released (not stored) due to the short circuit between the secondary output winding S4, so that the switching transistor Q operates in an oscillating manner. will be stopped and that state will continue. Therefore, the output voltage is cut off, making it possible to protect the load and prevent damage to the converter itself.

Here, the diode D2 inserted in series with the thyristor SCH is not necessary in principle, but it is used to protect the thyristor so that an excessive reverse voltage is not applied to the thyristor during normal operation. It fulfills the function of

Also, thyristor gate-cathode i#l Ic #$
The resistor R inserted in the thyristor is a gate parallel resistor, and functions to ensure the withstand voltage of the thyristor and prevent malfunction.

[Effects of the Invention] Since the present invention is an overvoltage protection circuit for a ringing choke converter configured as described above, the number of parts is extremely small, the circuit configuration is simplified, and therefore reliability is extremely high and assembly is easy. Therefore, it is possible to achieve excellent effects such as miniaturization.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of a ringing torque converter incorporating an overvoltage protection circuit according to the present invention, and FIG. 2 is a circuit diagram of a prior art. 1.11... Overvoltage protection circuit, T... Transformer, Q
,...Switching transistor for oscillation, Pl...
・Collector winding, P2... Feedback winding, S... Secondary output winding, D... Rectifier diode, C... Smoothing capacitor, SCR... Thyristor, ZD... Overvoltage detection Zener diode for.

Claims (1)

[Claims] 1. A thyristor is inserted between the secondary output windings of the ringing choke converter, and an overvoltage detection element is connected between the secondary rectification and smoothing output and the gate of the thyristor, and when overvoltage is detected, the overvoltage detection element An overvoltage protection circuit for a ringing choke converter, in which a thyristor is fired by the thyristor to short-circuit the secondary output windings of the transformer during the conduction period of the switching transistor, thereby stopping the self-excited oscillation operation of the converter. .