JPS6170812A - Muting circuit - Google Patents

Abstract

PURPOSE:To attain small-sized device by interrupting a signal at the pre-stage of an input transistor (TR) of a push-pull amplifier and cutting a bias of said output TR so as to apply muting. CONSTITUTION:When a control circuit 13 is activated and a control TR15 is turned on, muting TRs 17, 18 are turned on, and an input signal from input terminals 8, 9 is short-circuited by the muting TRs 17, 18 and then interrupted. Then a bias of TRS 2, 3 is cut off and the output TRs 2, 3 are turned off. Thus, muting is applied at the input side of the output TRs.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a muting circuit for, for example, a class B push-pull power amplifier used in a public address broadcasting system or the like.

Conventional configuration and problems thereof FIG. 1 shows a conventional miroating circuit. The configuration of this conventional example will be explained below with reference to FIG. In Fig. 1, l is an output transformer, 2.3 is an output transistor, 4 and 5 are emitter resistors, and the output transistors 2 and 3 are biased to class B by a bias circuit 6.7 and connected to an input terminal 8.9. are input with signals of opposite phase.

14 is a load. 10 is a relay contact, 11 is a relay that opens and closes the relay contact 10, 12 is a drive transistor, and 13 is a control circuit for muting. In this configuration, when holding a meeting, the control circuit 13
．． The drive transistor 12 and relay 11 open the relay contact 10 and cut off the signal to the load 14.

As mentioned above, in the conventional example, since the mini-W-T/G is performed by a relay, a relay with a large contact capacity according to the output is required, and the disadvantage is that the space occupied by the relay and the cost are large. 0 Objects of the Invention The present invention eliminates the drawbacks of the above-described embodiments, and aims to reduce the size and cost of the circuit.

Structure of the Invention In order to achieve the above object, the present invention is configured to perform muting by blocking a signal at the stage before the output transistor of a push-pull amplifier and cutting the bias of the output transistor. It is something.

DESCRIPTION OF THE EMBODIMENTS The configuration of an embodiment of the present invention will be described below with reference to the drawings. In FIG. 2, 1 to 9 and 13.14 are the same as in FIG. 15 is a control transistor;
The pace is connected to a control circuit 13. 17 and 18 are muting transistors whose collectors are connected to the paces of transistors 2 and 3, and whose emitters are connected to the junction of resistors 4 and 5;
a.

It is connected to the collector of the control transistor 15 via 16b.

Next, the operation of the above embodiment will be explained.

Now, when the control circuit 13 is activated and the control transistor 15 is turned on, the muting transistor 17.1 is turned on.
8 is also turned on, and input signals from input terminals 8 and 9 are short-circuited and cut off by muting transistors 17 and 18. At the same time, the bias of output transistor 2.3 is also 7
The output transistors 2 and 3 are also turned off.

In this embodiment, since muting is performed on the input side of the output transistor as described above, the muting circuit can be configured with small-signal transistors, making the circuit smaller and
The advantage is lower prices.

Effects of the Invention The present invention has the above-described configuration, and provides the following effects.

(a) Miniaturization of equipment because relays are not used.

Lower prices can be achieved.

fb) To cut off the output 2 register.

Compared to those that use relays, there is less power loss due to the excitation current of the transformer.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional muting circuit, and FIG. 2 is a circuit diagram of a mini-tiffuge circuit according to an embodiment of the present invention. 2.3... Output transistor, 13... Control circuit. 15... Control transistor, 17.18... Muting transistor. Name of agent: Patent attorney Toshio Nakao and 1 other person81
Figure 2

Claims (1)

[Claims] a push-pull amplifier and a muting transistor connected to the base of the output transistor of the amplifier;
A muting circuit comprising a control transistor that controls the muting transistor and a muting control circuit that drives and controls the control transistor.