JPH0739156A - Ringing choke converter circuit - Google Patents

Abstract

PURPOSE:To prevent a main transistor from being damaged when an overcurrent flows to the main transistor by a method wherein a resistance which is connected to an emitter for the main transistor and a capacitor which is connected to an emitter for a photocoupler are connected to a base for a control transistor. CONSTITUTION:By the collector current, of a photocoupler P, which is changed according to an output voltage, the charging time of a capacitor C is changed, the ON-time of a control transistor Tr2 is controlled on the basis of the voltage of the capacitor C, the base current of a main transistor Tr1 is controlled, and the output voltage is changed into a constant voltage. On the other hand, when an output current becomes excessive, the voltage drop of a resistance R become large, the control transistor Tr2 is turned on, the base current of the main transistor Tr1 is limited, and the generation of an overcurrent is prevented. Thereby, the number of components is reduced, and the circuit constitution can be made simple.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ringing choke converter circuit which can be simplified.

[0002]

2. Description of the Related Art FIG. 3 is a circuit diagram showing a typical example of a conventional ringing choke converter circuit.

In the conventional ringing choke converter circuit, as shown in FIG. 3, two control transistors Tr2 and Tr3 are incorporated to control the base current flowing in the main transistor Tr1. Here, one control transistor Tr2 is for overcurrent control, and the other control transistor Tr3 is for constant voltage.

[0004]

However, in this case, since there are two control transistors Tr2 and Tr3, there is a disadvantage that a complicated circuit configuration is inevitably inevitable.

In view of the above circumstances, it is an object of the present invention to provide a ringing choke converter circuit which is simplified by using only one control transistor.

[0006]

That is, the present invention has a main transistor (Tr1) and a photocoupler (P) whose collector current changes according to the output voltage, and the main transistor has a control transistor (Tr2). ) To control the base current of the main transistor,
A resistor (R) connected to the emitter of the main transistor and a capacitor (C) connected to the emitter of the photocoupler are connected to the base of the control transistor.

Numbers in parentheses are for convenience of showing corresponding elements in the drawings, and the present invention is not limited to the description in the drawings. This also applies to the “claims” and “action” columns.

[0008]

With the above-described structure, in the present invention, the function of the control transistor (Tr2) to limit the base current flowing through the main transistor (Tr1) has the function of limiting the base current to the main transistor. Also acts to prevent damage to the.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of a ringing choke converter circuit according to the present invention, and FIG. 2 is FIG.
4 is a graph showing waveforms at various parts of the ringing choke converter circuit shown in FIG.

In the ringing choke converter circuit according to the present invention, as shown in FIG. 1, the voltage drop of the resistor R connected to the emitter of the main transistor Tr1 also changes depending on the output voltage of the collector current of the photocoupler P. Then, it is noted that the capacitor C is charged and discharged with a triangular wave, and this is applied to the base of the control transistor Tr2.

That is, as shown in FIG.
Since the collector current controls the charging time of the capacitor C, T _on according to the output voltage can be obtained. As a result, the waveform of the collector-emitter voltage V _CE of the main transistor Tr1 becomes as shown in FIG. 2, and the constant voltage can be obtained.

On the other hand, when the output current is increased, the voltage drop of the resistor R is increased, and when the base of the control transistor Tr2 is about 0.6V, the control transistor Tr2 is increased.
2 continues to turn on and limits the base current flowing through the main transistor Tr1. As a result, the main transistor T
It is possible to prevent the occurrence of a situation in which an overcurrent flows through r1 and damage occurs.

In order to confirm the above-mentioned effects, a ringing choke converter circuit according to the present invention (hereinafter abbreviated as "invention circuit") and a conventional ringing choke converter circuit as shown in FIG. 3 ( In the following, abbreviated as "conventional circuit"), input voltage AC85V-A
C132V (rated 100V), output + 5V, 0.1-1
Each of the power supplies A was manufactured, and the constant voltage level and the overcurrent protection characteristic were compared.

As a result, Table 1 shows the constant voltage levels.
As described above, the circuit of the present invention is the same as the conventional circuit, and both have the same overcurrent protection characteristics.

[0016]

[Table 1]

[0017]

As described above, according to the present invention,
It has a main transistor Tr1 and a photocoupler P whose collector current changes according to the output voltage. A control transistor Tr2 is connected to the main transistor Tr1 so as to control the base current of the main transistor Tr1. A resistor R connected to the emitter of Tr1 and a capacitor C connected to the emitter of the photocoupler P are connected to the control transistor Tr2.
Since it is configured by connecting to the base of
The function of limiting the base current flowing through the main transistor Tr1 by the r2 is to maintain the main transistor Tr1 at a constant voltage.
Since this is also done to prevent damage to r1, 1
It is possible to provide a ringing choke converter circuit which is simplified by the individual control transistors Tr2.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a ringing choke converter circuit according to the present invention.

FIG. 2 is a graph showing waveforms at various parts of the ringing choke converter circuit shown in FIG.

FIG. 3 is a circuit diagram showing a typical example of a conventional ringing choke converter circuit.

[Explanation of symbols]

 C ... Capacitor P ... Photo coupler R ... Resistor Tr1 ... Main transistor Tr2 ... Control transistor

Claims (1)

[Claims] 1. A main transistor (Tr1), and a photocoupler (P) whose collector current changes according to an output voltage, wherein the main transistor has a control transistor (Tr2).
Is connected so as to control the base current of the main transistor, and a resistor (R) connected to the emitter of the main transistor and a capacitor (C) connected to the emitter of the photocoupler are connected to the control transistor. Ringing choke converter circuit configured by connecting to the base.