JPH0528808Y2 - - Google Patents

Description

[Detailed description of the invention] (a) Industrial application field The present invention relates to a muting circuit.

(b) Prior Art Conventionally, audio equipment has been provided with a muting circuit that shunts or cuts off a low frequency signal line in order to prevent the generation of shock noise when power is turned on or off. This type of muting circuit is known, for example, as disclosed in Japanese Patent Application Laid-Open No. 112707/1983 (H03F1/00).

By the way, mutating circuits generally include a circuit that generates a control signal when the power is turned on and a circuit that generates a control signal when the power is turned off, in order to reliably prevent shock noise when the power is turned on and off.

However, when a control signal generating circuit is provided in this manner, the problem arises that the circuit configuration becomes complicated and the cost increases.

(c) Problems to be solved by the invention In view of the above-mentioned points, the present invention aims to provide a muting circuit that can reliably achieve muting when the power is turned on and off using a single control signal generation circuit. It is.

(d) Means for solving the problem In view of the above points, the present invention provides a switching transistor disposed between the power supply line and the ground,
a first time constant circuit provided between the base of the switching transistor and the power supply line; a second time constant circuit including a capacitor provided between the base of the switching transistor and ground; It consists of a muting drive transistor controlled by the output of.

(e) Effect In the above configuration, when the power is turned on, the mutating circuit is driven by immediately turning on the mutating driving transistor, and after a time determined by the time constant of the first time constant circuit, the switching transistor is turned on. By turning on, the muting drive transistor is turned off. That is, the muting drive transistor is turned on until a time determined by the time constant of the first time constant circuit elapses after the power is turned on, thereby reliably eliminating the shock noise when the power is turned on.

Further, when the power is turned off, the switching transistor is immediately turned off by the charging potential of the capacitor of the second time constant circuit, and the muting drive transistor is turned on.

(f) Example The figure shows an example of the present invention. In the figure, 1 is a switching transistor disposed between the power supply line 2 and the ground, 3 is a first time constant circuit disposed between the base of the switching transistor 1 and the power supply line 2, and a capacitor 4 and a resistor. It is composed of 5. 6 is a second time constant circuit including a capacitor 7 provided between the base of the switching transistor 1 and the ground, 8 is a protection diode for the switching transistor 1, 9 is a reverse current prevention diode, and 10 and 11 are switching transistors. Bias resistor 1, 12 and 13 are resistors connected to the collector of switching transistor 1, and the midpoint of the connection is, for example, controller 1 for controlling the operation of a synthesizer receiver.
Connected to 4. Reference numeral 15 denotes a muting drive transistor controlled by the output of the switching transistor 1, whose collector output is supplied to a muting transistor (not shown). 16 and 17 are bias resistors, and 18 is a backflow prevention diode.

Next, the operation will be explained.

When the power is turned on, a current is supplied to the base of the switching transistor 1 through the first time constant circuit 3 , so that the switching transistor 1 is in a reverse bias state and is off. At this time, the base current flows through the muting drive transistor 15 through the resistor 17, the diode 18, and the resistors 12 and 13, so it is biased and turned on, thereby driving the subsequent muting transistor.

When charging of the capacitor 4 constituting the first time constant circuit 3 is completed, that is, when a time determined by the time constant of the first time constant circuit 3 has elapsed, the switching transistor 1 is biased by the resistors 10 and 11. It turns on.

At this time, the capacitor 7 constituting the second time constant circuit 6 is also charged, but this does not substantially affect the operation of the switching transistor 1.

When the switching transistor 1 is turned on in this manner, its collector output becomes a high level, and this high level signal is voltage-divided by the resistors 12 and 13 and then supplied to the controller 14. The controller 14 outputs, for example, a mute signal based on the high level signal.

At the same time, when the collector output of the switching transistor 1 becomes high level, the reverse current prevention diode 18 becomes reverse biased and turned off.

Therefore, the mutating drive transistor 1
The bias line 5 is cut off, and the muting drive transistor 15 is turned off.

On the other hand, when the power is turned off in such a state, the charging potential of the capacitor 7 constituting the second time constant circuit 6 is temporarily held at the initial value by the action of the reverse current prevention diode 9, so that the power supply voltage decreases. As a result, the switching transistor 1 is reverse biased and turned off.

Therefore, the collector output of the switching transistor 1 is not generated, and the muting drive transistor 15 is biased and turned on.

(G) Effects of the invention According to the invention, a switching transistor is provided between a power supply line and the ground, and a first time constant circuit is provided between the base of the switching transistor and the power supply line. , a second time constant circuit including a capacitor provided between the base of the switching transistor and ground, and a muting drive transistor controlled by the output of the switching transistor, and when the power is turned on, the muting is immediately activated. After the driving transistor is turned on and a time determined by the time constant of the first time constant circuit has elapsed, the switching transistor is turned on and the muting driving transistor is turned off, and when the power is turned off, the second time constant circuit Since the switching transistor is immediately turned off by the charging potential of the capacitor, and the muting drive transistor is then turned on, it is possible to reliably prevent the shock noise when the power is turned on and off with a simple circuit configuration. I can do it.

[Brief explanation of drawings]

The figure shows an embodiment of the present invention. 1... Switching transistor, 3 ... First
time constant circuit, 6 ... second time constant circuit, 15... mutating drive transistor.

Claims (1)

[Scope of utility model registration request] a switching transistor disposed between the power supply line and the ground; a first time constant circuit disposed between the base of the switching transistor and the power supply line; and a first time constant circuit disposed between the base of the switching transistor and the ground. a second time constant circuit including a capacitor, a backflow prevention diode, and a muting drive transistor controlled by the output of the switching transistor, which immediately turns on the muting drive transistor when the power is turned on, and After the time determined by the time constant of the first time constant circuit has elapsed,
The switching transistor is turned on, thereby turning off the muting drive transistor, and when the power is turned off, the charging potential of the capacitor of the second time constant circuit is held by the reverse current prevention diode, thereby turning on the switching transistor. A muting circuit characterized in that it immediately turns off and then turns on a mutating drive transistor.