JPS5914824Y2 - power circuit - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a power supply circuit used in audio equipment and the like.

For example, the following is a power supply circuit used in audio equipment.

□The tm circuit has a control transistor whose base is held at a constant voltage inserted in series with a pulsating current circuit, and improves regulation characteristics by supplying power to the load via the control transistor. .

A specific example of such a conventional circuit is shown in FIG.

In the figure, 1 is a power transformer, 2 is a rectifier circuit, 3 is a control transistor, 5 is an output terminal, 6 is a smoothing capacitor, 7 is a load, and 8 is a Zener diode.

In such a power supply circuit, the input voltage waveform to the collector of the control transistor 3, the output voltage waveform of the output terminal 5,
The waveforms of the current flowing through the control transistor 3 are as shown by the solid line and broken line in FIG. 1A, and the solid line in FIG. 1B, respectively.

That is, in section A on the rising side of the waveform, the control transistor is completely turned on, and the collector-emitter voltage is suppressed to a low level by the internal impedance of the power transformer or the like provided on the input side.

On the other hand, at the beginning of the section following section A, the collector current flows slowly and the collector-emitter quantity pressure also increases.

However, in section A, the control transistor is completely turned on and the voltage between the collector and emitter is suppressed to a low level, so the heat loss of the control transistor is small. However, at the beginning of section, the collector current flows slowly and the voltage between the collector and emitter increases. Therefore, the heat loss of the control transistor becomes extremely large.

That is, the conventional power supply circuit has the disadvantage that the heat loss of the control transistor is large and the heat sink of the control transistor is large.

This idea has been made in view of the above points, and aims to provide a power supply circuit in which the heat loss of the control transistor is small and the heat dissipation plate of the control transistor can be made small.

Examples of this invention will be described below with reference to the drawings.

FIG. 2 is a circuit diagram showing an embodiment of this invention. In this figure, 1 is a power transformer, the secondary winding of which is connected to a rectifier circuit 2, and the negative side output of this rectifier circuit 2. is grounded.

The positive side output of the rectifier circuit 2 is an NPN type control transistor 3.
The emitter of the control transistor 3 is connected to the output terminal 5 via a resistor 4.
That is, the control transistor 3 is inserted in series in the ripple current circuit.

Note that a smoothing capacitor 6 and a load 7 are connected between the output terminal 5 and the ground.

The base of the control transistor 3 is connected to the cathode side of a series circuit of reference Zener diodes 8 and 9.
The anode side of this reference Zener diode 8°9 series circuit is grounded.

Further, a series circuit of resistors 10 and 11 is connected between the collector and base of the control transistor 3, and the resistors 10 and 1 are connected in series.
The voltage dividing point a of 1 is connected to the base of an NPN type transistor 12.

The emitter of this transistor 22 is the control transistor 3.
is connected to the collector of the resistor 13, and the collector is connected to the resistor 13.
．． 14 in series to ground.

Further, the voltage dividing point between the resistors 13 and 14 is connected to the base of an NPN type switching transistor 15, and the collector of this switching transistor 15 is connected to the midpoint C between the reference Zener diodes 8 and 9. At the same time, the emitter is grounded.

Next, the operation of the power supply circuit configured as described above will be explained.

In this power supply circuit, power is supplied to the load 7 via the control transistor 3 inserted in the pulsating current circuit.

On the other hand, the resistor 10.11 and the transistor 12 detect the voltage between the collector and emitter of the control transistor 3 based on the voltage between the collector and base of the control transistor 3, and when the voltage between the collector and emitter becomes large,
Transistor 12 turns on.

When this transistor 12 is turned on, the potential at the voltage dividing point between the resistors 13 and 14 increases, so the switching transistor 15 is turned on. When this switching transistor 15 is turned on, the reference Zener diode 9 is short-circuited. The control transistor 3 is turned off by lowering the base potential and entering a reverse bias state.

Therefore, the control transistor 3 in this power supply circuit
The input voltage waveform to the collector, the output voltage waveform at the output terminal 5, and the current waveform flowing through the control transistor 3 are shown by the solid line and broken line in Figure 3A, and the solid line in Figure 3B, respectively.In this case, the waveform rise In the section A on the side, the control transistor 3 is completely turned on as in the conventional case, and the collector-emitter voltage is kept low by the internal impedance of the power transformer 1 on the input side.

On the other hand, in the conventional power supply circuit, at the beginning of a section where the collector current flows slowly and the collector-emitter voltage increases, the control transistor 3 is turned off and the current becomes zero.

Therefore, according to such a power supply circuit, the control transistor 3 is operated only in the efficient part, and the control transistor 3 is turned off in the other parts, so that the heat loss of the control transistor 3 is small and the control transistor 3 is operated. The heat sink can be made smaller.

In the above embodiment, the voltage between the collector and emitter of the control transistor 3 is detected by the voltage between the collector and base, but in the case of directly detecting the voltage between the collector and emitter, the other method shown in FIG. This is a circuit diagram shown in an example.

That is, a series circuit of resistors 10' and 11' is connected between the collector and emitter of the control transistor 3, and a voltage dividing point a' between the resistors 10' and 11' is connected to the base of the transistor 12.

Note that in other embodiments, the control transistor 3
A resistor 16 is connected between the collector and base of the resistor 16 so that current flows through the reference Zener diodes 8 and 9.

As described in detail above, according to this invention, it is possible to provide a power supply circuit in which the heat loss of the control transistor is small and the heat sink of the control transistor can be made small.

[Brief explanation of the drawing]

1A and 1B are diagrams of the input/output voltage waveforms of the control transistor and the current waveforms flowing through the control transistor in a conventional power supply circuit, FIG. 2 is a circuit diagram showing an embodiment of the power supply circuit according to this invention, and FIG. 3A and B are input/output voltage waveforms of the control transistor and current waveforms flowing through the control transistor in the power supply circuit of the above embodiment, and FIG. 4 is a circuit diagram showing another embodiment of the invention. FIG. 5 shows a specific example of a conventional power supply circuit. 3... Control transistor, 8, 9... Zener diode for reference, 10.11.10', 11'... Resistor, 12... Transistor, 15... Switching transistor.

Claims (1)

[Scope of utility model registration request] A control transistor inserted in series in the pulsating current circuit, a reference Zener diode connected to the base of the control transistor, means for detecting the collector-emitter voltage of the control transistor, and a circuit controlled by the detection means. A power supply circuit comprising a switching transistor that shorts the Zener diode.