JPS62175007A - Power amplifier protecting device - Google Patents

Abstract

PURPOSE:To prevent the destruction of a transistor for amplifying an electric power by providing a photocoupler for detecting an abnormal voltage between a collector and an emitter of a transistor for amplifying the electric power and interrupting a base electric current by the signal to obtain the AND of the signal and the pulse signal of a pulse oscillator. CONSTITUTION:The voltage between a collector and an emitter is increased, a photocoupler 6 is turned on by the voltage and an abnormal voltage is detected. The AND of the signal to detect the abnormal voltage and the pulse signal from a pulse oscillator 1 is generated by a logic circuit 7. When a transistor 2 for amplifying the electric power from the logic circuit 7 is on and the photocoupler 6 detects the abnormal voltage, a switch 8 is operated. Thus, the base electric current supplied to the transistor for amplifying the electric power is interrupted, the transistor 2 for amplifying the electric power is turned off and destruction is prevented at the time of the abnormality.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a protection device for a power amplifier using a transistor.

[Conventional technology]

FIG. 2 shows the configuration of a conventional power amplifier.

In the figure, (1) is a pulse oscillator, (2) is a power amplification transistor, (3) is a load, (4) is a power supply, and (5) is a power amplification transistor.
is the base current of the power amplification transistor.

Conventionally, when a base current (5) is supplied from a pulse oscillator (1) to a power amplification transistor (2), the power amplification transistor (2) is turned on due to switching operation, and the load ( 3) was being supplied with power from the power supply (4).

[Problem that the invention seeks to solve]

By the way, in this conventional device, if the base current (5) sent from the pulse oscillator (1) to the power amplification transistor (2) becomes small for some reason,
The problem is that the relationship between the collector current and the collector-emitter voltage of the power amplification transistor (2) changes as shown in Figure 3, which increases the collector-emitter voltage and destroys the power amplification transistor. was there.

This invention was made in order to solve one or more of the conventional problems, and when the voltage between the concrete emitter increases abnormally when the transistor (2) is in the on state, the power amplifying transistor The purpose is to prevent (2) from being broken.

[Failure to solve the problem]

The power amplifier protection device according to the present invention includes a photocoupler that is arranged between the concrete emitters of the power amplifying transistor (2), which detects when the voltage between the concrete emitters exceeds a certain value.

[Function] In this invention, when the power amplification transistor (2) is in an on state and the voltage between the concrete emitters increases abnormally, this is detected and the base current (5) is cut off, and the power amplification transistor (2) is turned on. By turning off the transistor (2) for
'sr, the force amplification transistor (2) can be prevented from being destroyed.

〔Example〕

FIG. 1 shows an example of the configuration of a power amplifier in which the present invention is implemented. In the figure, (l) to (5) are the same as in FIG. 2, i6) is a photocoupler, (7) is a logic circuit, (8) is a switch, and (9) is an abnormal voltage setting resistor.

The operation of the power amplifier device when the pulse oscillation a(1) is operating normally is the same as in the conventional case.

Now, what if the pulse oscillator (1) malfunctions for some reason and the output current becomes small?

When the power amplifying transistor (2) is in the on state, the relationship between the collector-emitter voltage and the collector current changes as shown in FIG. 3, and the voltage between the concrete emitter increases.

This voltage turns on the photocoupler (6) and detects the abnormal voltage. A logic circuit (7) generates an AND between the signal detecting the abnormal voltage and the pulse signal from the pulse oscillator tl)Z>4. When the power amplification transistor (2) from the logic circuit (7) is on and the photocoupler (6) detects abnormal voltage, the switch (8)
make it work. By doing so, the base current supplied to the power amplifying transistor (2) is cut off, the power amplifying transistor (2) is turned off, and it is prevented from being destroyed in the event of an abnormality.

The abnormal voltage setting resistor (9) is a power amplification transistor (
The voltage at which the photocoupler (6) is turned on can be set by dividing the voltage between the collector and emitter of 2). Therefore, power amplification transistor (2)
It is possible to set the voltage between the conctal emitters at which it is considered abnormal.

[Effects of the Invention] As explained above, in this invention, a photocoupler (6) for abnormal voltage detection is installed between the collector and emitter of the power amplification transistor (2), and the signal is connected to the pulse oscillator +1). By the signal obtained by logical integration with the pulse signal,
Since the base current (5) is cut off, the tIi force amplifying transistor (2) is turned off and can be prevented from being destroyed.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an example of the configuration of a power amplifier circuit showing an embodiment of the present invention, Fig. 2 is a diagram showing an example of the configuration of a conventional single-power amplifier circuit, and Fig. 3 is a diagram showing an example of the configuration of a conventional single-power amplifier circuit. 2 is a diagram showing the relationship between collector-emitter voltage and collector' current of a transistor. FIG. In the figure, (I) is a pulse oscillator, (2) is a power amplification transistor, (3) is a load, (4) is a power supply, and (5) is a base current. (6) is a photocoupler, (7) is a logic circuit, and (8) is a switch. Note that the same or corresponding parts in the two figures are designated by the same reference numerals.

Claims (1)

[Claims] A power amplification transistor, a pulse oscillator that gives switching commands to the transistor, a photocoupler that detects the voltage between the collector and emitter of the power transistor, and a logic circuit that generates the logical sum of the signal from the pulse oscillator and the signal from the photocoupler. and a switch that receives a signal from the logic circuit and cuts off the base current sent to the power transistor.If the voltage between the collector and emitter of the power amplification transistor increases abnormally, the power amplification transistor A power amplifier protection device characterized by preventing transistors from being destroyed.