JPS5932221Y2 - Ringing choke converter - Google Patents

Description

[Detailed explanation of the idea] The present invention relates to a ringing choke converter.

As illustrated in FIG. 1, the ringing choke converter applies positive feedback from the collector side to the base side of the transistor Q1 through the windings N, N3 of the transformer T1, and
By causing a blocking oscillation operation, the DC input applied to the input terminals a and b is switched, and the winding N of the transformer T1 is switched during the off period of the transistor Q1.
2. The configuration is such that the output is taken out via the diode D1.

R1, R2, R3 are resistors, C1, C2 are capacitors, D
2. D3 is a Zener diode D4. D, Iri diodes, these are the transistor Qt, the winding N1 . Together with N3, it constitutes a blocking oscillation circuit.

In the ringing choke converter described above, when the output current becomes excessive, the amount of positive feedback fed back to the base side of the transistor Q0 via the winding N3 increases, and the base current IB1 of the transistor Q1 increases. , collector current I.

1 and output current 2 may exceed the allowable value.

Therefore, conventionally, an overcurrent protection circuit A is provided on the base side of the transistor Q1.

This overcurrent protection circuit A includes a transistor Q for current control.
The collector of 2 is connected to the transistor Q through the diode D6.
The emitter and base of the transistor Q2 are respectively connected to both ends of a resistor R4 inserted and connected in series to the power supply line.

R5 is the base resistance of transistor Q2.

When the overcurrent protection circuit A as described above is provided, the collector current Ic of the transistor Q1! 1 increases, the resistance R
4, the voltage drop increases, and transistor Q2
Since the base-emitter potential difference becomes large, the base current of the transistor Q1 is bypassed to the transistor Q2 side via the diode D6.

As a result, the base current IB1 of the transistor Q1 decreases, and the collector current I.

1 is suppressed, and at the same time, the output current proportional to this is also limited.

However, since the above-mentioned overcurrent protection circuit A detects only the peak value of the collector current Ic1 and limits it, when the input voltage increases, the overcurrent droop point becomes the second point.
As shown in the figure, there is a drawback that the output current moves in the opposite direction, resulting in an increase in output power, and the electrical stress on the transistor Q1% transformer T1 or the diode D1 increases.

The present invention aims to eliminate the above-mentioned drawbacks and provide a ringing choke converter equipped with an overcurrent protection circuit that can limit the output current without causing an increase in output power even if the input voltage fluctuates. shall be.

In order to achieve the above object, the ringing choke converter according to the present invention superimposes a signal proportional to the input voltage and a signal proportional to the collector current of the transistor on the base circuit of the transistor constituting the blocking oscillation circuit. The present invention is characterized by comprising an overcurrent protection circuit that applies a signal to the base of a current control transistor to drive it, and controls the base current of the transistor constituting the blocking oscillation circuit using the current control transistor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The contents of the present invention will be described in detail below with reference to the accompanying drawings, which are examples.

FIG. 3 shows an electrical circuit connection diagram of a ringing choke converter according to the present invention.

In the figure, the same reference numerals as in FIG. 1 indicate components having the same functions.

In this embodiment, a resistor R6 is connected between the base of the transistor Q2 of the overcurrent protection circuit A and the resistor R4 for collector current detection, and a connection point between the resistor R6 and the base of the transistor Q2 is connected. d via resistor R7,
The circuit configuration is such that the control winding N3 of the transformer T1 and the diode D4 are electrically connected to the connection point e.

Next, the operation of the ringing choke converter according to the present invention will be explained with reference to the voltage waveform diagram shown in FIG.

When the input voltage Vin applied to input terminals a and b increases with a certain load RL connected to the output side of the ringing choke converter, the voltage Vf induced in the control winding N3 of the transformer T1 also increases. As shown in FIG. 4 R1, the voltage increases by ΔVf in proportion to the fluctuation of the input voltage.

On the other hand, as shown in FIG. 4 R2, the collector current of the transistor Q1 is across both ends of the current detection resistor R4.

A voltage proportional to 1 is generated. These two voltage signals are suitably superimposed by the resistors R6 and R7, and the voltage Vp at the connection point d to the emitter of the transistor Q2 is
The result is as shown in FIG.

When the voltage VpO value becomes sufficiently higher than the on-voltage VBE between the base and emitter of the transistor Q20, the transistor Q2 is turned on.The base current of the transistor Q1 is bypassed to the transistor Q2 side through the diode D6. Q1 is the cut off.

The voltage Vp at the connection point d, which turns on the transistor Q2, increases as the input voltage increases, as can be understood from a1 to a3 in FIG. 4. Therefore, as the input voltage increases, the collector current Ic1 decreases. If an overcurrent limiting operation is performed and the input voltage becomes low, the collector current ■.

After the number 1 becomes thicker, the overcurrent limiting operation will be performed.

In this case, since the output current is proportional to the product of the input voltage and the collector current, overcurrent protection can be performed with almost the same output current despite fluctuations in the input voltage.

FIG. 5 is an output characteristic diagram illustrating this, and shows that the overcurrent droop point is kept almost constant despite fluctuations in the input voltage.

Figures 6 and 7 show the ringing choke according to the present invention.
5 shows another embodiment of an overcurrent protection circuit for a converter.

In the embodiment shown in FIG. 6, the voltage signal is connected to diode D4.
In the embodiment shown in FIG. 7, the resistor R7 is connected to the line from which the voltage signal is taken out, as in the embodiment shown in FIG.
and Zener diode D7 are connected in series, and is substantially the same as that shown in FIG.

As explained in detail above, the ringing choke converter according to the present invention provides a signal in which a signal proportional to the input voltage and a signal proportional to the collector current of the transistor are superimposed on the base circuit of the transistor constituting the blocking oscillation circuit. is provided to the base of the current control transistor to drive it, and the current control transistor controls the base current of the transistor constituting the blocking oscillation circuit. Even if the voltage fluctuates, the overcurrent droop point can be kept at approximately the same position, suppressing an increase in output power, reducing electrical stress on transistors, transformers, or diodes, and improving reliability.

[Brief Description of the Drawings] Fig. 1 is an electric circuit connection diagram of a conventional ringing choke converter, Fig. 2 is an output characteristic diagram when the input voltage is varied, and Fig. 3 is a ringing choke converter according to the present invention. Circuit diagram of choke converter, Figure 4a,,a2. A3 is the voltage waveform diagram of each part, and Figure 5 is the output characteristic diagram.
Figure 6 1. FIG. 7 shows circuit diagrams of other embodiments of the overcurrent protection circuit section. R1-R7...Resistor, 01-C3...Capacitor,
D2-D3... Zener diode, Dll D4
~D6...Diode, Ql, Q2...Transistor, T1...Transformer, N,, N2. N3...Winding, A...Overcurrent protection circuit.

Claims (2)

[Scope of utility model registration request] (1) A signal in which a signal proportional to the input voltage and a signal proportional to the collector current of the transistor are superimposed is applied to the base circuit of a transistor constituting the blocking oscillator circuit to drive the base circuit of the current control transistor. . A ringing choke converter comprising: an overcurrent protection circuit that controls a base current of the transistor constituting the blocking oscillation circuit by the current control transistor. (2) The overcurrent protection circuit is characterized in that the voltage generated in the control winding of the transformer constituting the blocking oscillation circuit is a signal proportional to the input voltage. Ringing choke converter as described.