JPS6352482B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit for preventing damage to an acoustic amplifier due to a short circuit.

In a conventional differential input type acoustic amplifier (hereinafter referred to as an acoustic amplifier), if the output end is shorted to the power supply end (hereinafter referred to as a ground fault) or shorted to the ground end (hereinafter referred to as a ground fault), the final stage transistor It is known that overcurrent can flow and lead to destruction. As such an acoustic amplifier, the one shown in FIG. 1 is known.

That is, the bias of the non-inverting input terminal 1 of the acoustic amplifier 12 is applied to the resistor 7 from the bleeder circuit of the resistors 5 and 6.
The capacitor 10 is a power supply ripple prevention capacitor. The acoustic signal inputted from the non-inverting input terminal 1 is amplified by the acoustic amplifier 12 to a gain determined by the resistors 8 and 9 and the capacitor 11, and is output from the output terminal 2.
A power source is connected to the power source terminal 3, and a ground terminal 4 is connected to a ground potential.

In the acoustic amplifier with the above circuit configuration, if the output end 2 is shorted to supply or ground, an excessive current will flow to the final stage transistor, and the power loss of the final stage transistor will increase.
It had the disadvantage of destroying the final stage transistor or its peripheral circuits.

The present invention relates to an acoustic amplifier having a protection device that prevents an output transistor from being destroyed in the event that an output terminal is shorted to power or ground by comparing the potential of a midpoint of a bleeder circuit and a feedback capacitor.

Next, the present invention will be explained using FIG. 2. still,
The same parts as in FIG. 1 are designated by the same numbers.

The non-inverting input terminal 1 of the acoustic amplifier 12 is biased from the midpoint of the bleeder circuit formed by the resistors 5 and 6 to the resistor 7.
The acoustic signal input from the non-inverting input terminal 1 is passed through the acoustic amplifier 12 to the resistors 8, 9,
The signal is amplified by a gain determined by the capacitor 11. The midpoint of the bleeder circuit made up of resistors 5 and 6,
The outputs of comparators 13 and 15 whose input is the connection point between the feedback capacitor 11 and the resistor 8 are connected to switching circuits 14 and 16, respectively, and the output terminal 2
Cuts off the base bias of the final stage transistor in the event of a power supply or ground fault. The quick charging circuit 17 charges the capacitor 11 in order to start the circuit when the acoustic amplifier 12 is powered on. A power source is connected to the power source terminal 3, and a ground terminal 4 is connected to a ground potential.

If the output terminal 2 of the acoustic amplifier with the above circuit configuration is shorted to power or ground, the DC potential of the feedback capacitor 11 will deviate significantly from 1/2 of the original power supply voltage.
Using this difference in potential, the midpoint voltage of the bleeder circuit is used as a reference voltage, the DC potential of the feedback capacitor 11 and the reference potential are compared using comparators 13 and 15, and the outputs of the comparators 13 and 15 are used to control the switching circuit 14. , 16 and cut off the final stage transistor of the acoustic amplifier 12.

When the acoustic amplifier 12 is powered on, the DC potential of the feedback capacitor 11 is 0V, so the final stage transistor is cut off and the circuit does not start. Therefore, the quick charging circuit 17 is used to charge the feedback capacitor 11 at startup. do. Quick charging circuit 1
7 has a control terminal connected to the connection point of resistors 5 and 6, that is, one end of the capacitor 10, and when the power is turned on, when the charge of the capacitor 10 is zero, it becomes operational and the capacitor is connected through the resistor 8. Charge 11 quickly. Capacitor 10 is resistor 5
When the charging circuit 17 reaches a predetermined charge level, the charging circuit 17 becomes inactive and the capacitor 11
Stop charging.

Next, a specific embodiment of the present invention will be described using FIG. The base bias of the transistor 19 of the first stage differential amplifier constituted by the transistors 19 and 20 is applied from the midpoint of the bleeder circuit of the resistors 5 and 6 via the resistor 7, and the capacitor 10 is for preventing power supply ripple. Resistor 18 is a load resistance of the first stage differential amplifier. The acoustic signal inputted from the non-inverting input terminal 1 connected to the base of the transistor 19 is amplified by the first stage differential amplifier of transistors 19 and 20, and is connected in a single-ended push-pull format via the driver transistor 28. and two output stage transistors 36, 35 and 37, 39. Diode 29,3
0 and 31 are for bias of the output stage transistor. Resistor 22, 23, 25, 33 Diode 2
6, 27 and transistors 24, 32 are constant current circuits for determining the current of the first stage differential amplifier and for loading the driver transistor 28. The connection point between the emitter of the transistor 38 and the collector of the transistor 39 is connected to the output terminal 2, and a resistor 9 is connected to the output terminal from the output terminal.
connected to the base of the transistor 20 via
Resistors 9 and 8 and a capacitor 11 constitute a feedback circuit. Resistor 40 charges capacitor 11 during startup. A transistor 4 whose inputs are the midpoint of the bleeder circuit and the non-grounded side of the feedback capacitor 11.
1, 42 and resistors 43, 44 is connected to the base of the switching transistor 34, and when the output terminal 2 is shorted to power, the switching transistor 34 is turned on, and therefore the transistors 37 and 39 are turned off. and transistor 3
7,39 to prevent destruction.

Similarly, transistors 45, 46, resistors 47, 4
The output of the second comparator consisting of . Prevent destruction. The transistor 21 is turned on when the acoustic amplifier is powered on, and quickly charges the capacitor 11. That is, since the base of the transistor 21 is connected to one end of the capacitor 10 as a control terminal, it is at zero potential when the power is turned on, while the emitter is given the potential at the connection point of the resistors 22 and 23, and as a result,
Transistor 21 becomes conductive and charges capacitor 11 via resistor 8 in response to power-on. Capacitor 10 is charged by resistor 5 and transistor 21
Since the base and emitter of the transistor 21 are reverse biased, the transistor 21 is cut off during normal operation.

Although specific embodiments have been described above, the number of comparator circuits may be one. Furthermore, it is easy to integrate the circuit, and it can be integrated without increasing the number of external circuits.

[Brief explanation of the drawing]

FIG. 1 is a basic configuration diagram of a conventional differential input type acoustic amplifier. FIG. 2 is a basic configuration diagram of a differential input type acoustic amplifier according to the present invention. FIG. 3 is a circuit diagram of a specific embodiment using the present invention. 1...Non-inverting input terminal, 2...Output terminal, 3...Power supply terminal, 4...Grounding terminal, 5, 6, 7, 8, 9, 1
8, 22, 23, 25, 33, 40, 43, 4
4,47,48...Resistor, 10,11...Capacitor, 19,20,21,28,34,35,3
6, 37, 38, 39, 41, 42, 45, 46
...Transistor, 26, 27, 29, 30, 3
1... Diode, 12... Differential input type acoustic amplifier, 13, 15... Comparator, 14, 16...
...switching circuit, 17...quick charging circuit.

Claims (1)

[Claims] 1 A differential amplifier circuit having an input terminal and a feedback terminal, a first output stage transistor connected between a power supply terminal and an output terminal, and a second output stage connected between the output terminal and a ground point. a transistor, a drive circuit that drives the first and second output stage transistors in a push-pull manner in response to the output of the differential amplifier circuit, and a power supply ripple prevention device connected between the bias voltage generation terminal and the ground point. a bias circuit having a capacitor for generating a bias voltage at the bias voltage generation terminal; means for supplying an input signal together with the bias voltage to the input terminal of the differential amplifier circuit; and between the output terminal and the feedback terminal. a first resistor connected to the feedback terminal; a second resistor having one end connected to the feedback terminal; a feedback capacitor having one end connected to the other end of the second resistor and the other end directly connected to the ground point; A reference voltage generation circuit that generates a reference voltage, and the feedback capacitor are rapidly charged in response to a potential difference between the voltage of the bias voltage generation terminal of the bias circuit and the reference voltage, and shut off when the potential difference becomes smaller than a predetermined value. The acoustic amplifier is equipped with a charging circuit that detects a power supply fault or a ground fault at the output terminal by comparing the bias voltage and the voltage at the one end of the feedback capacitor, and generates a power supply detection signal or a power supply fault detection signal. a comparator that generates a ground fault detection signal; and in response to the power fault detection signal, the second output stage transistor is set to a cutoff state, and in response to the ground fault detection signal, the first output stage transistor is set to a cutoff state. An acoustic amplifier further comprising a control means for controlling the acoustic amplifier.