JPS6148207A - Output mute control circuit - Google Patents

Abstract

PURPOSE:To prevent output of click noise surely by providing a capacitor for a power-off detection capacitor and a smoothing capacitor in common to a power supply circuit. CONSTITUTION:When a power siwtch 8 is turned off, a microcomputer power supply circuit 6 is turned off to stop power supply to a microcomputer. Transistors (TRs) 2, 3 are turned off at the same time, a TR4 is turned on, TRs 5, 6 are turned off, an amplifier power circuit 5 is turned off to stop the power supply. As a result, a smoothing capacitor C3 starts discharging the electric charge charged therein, but since the TR5, 6 are both turned off, the discharge current flows to a mute control circuit 3. Then the control circuit 3 turns on a mute TR2 to keep this state until the discharge current is terminated. Thus, the click noise is prevented from being outputted surely.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an output mute control circuit applied to audio devices and the like.

[Conventional technology]

When turning the audio device on and off, the click sound is output as is, which is annoying.

Therefore, even if the power switch is operated, the output of the click sound can be prevented by instantaneously stopping the signal from the signal line. FIG. 2 shows a conventional output mute control circuit used for this purpose. In Fig. 2, 1 is a signal line of the audio device, 2 is a muting transistor for controlling this signal line, 3 is a control circuit for controlling the muting transistor 2, 4 is a power-off detection circuit, and 5 is an amplifier. Power supply circuit, 6 is microcomputer power supply circuit, 7 is rectifier circuit A, 8
8 is a power switch, C1 is a capacitor included in the power-off detection circuit 4, C2 is a capacitor included in the amplifier power supply circuit 5, and TR1 is a transistor.

The amplifier power supply circuit 5 is for supplying power to the amplifier section of the audio device, and the microcomputer power supply circuit 6 is for supplying power to the microcomputer section incorporated in the control circuit 3 to perform predetermined operations. be.

In the above configuration, the power switch 8 is turned off while AC power is maintained in the AC power input circuit 7, and the operation continues until the power switch 8 is turned off. is turned off, and the supply of power to the microcomputer of the control circuit 3 is stopped.At the same time, the power supply to the power-off detection circuit 4 is also stopped, so at this moment, the capacitor C□, which has been charged up to that point, starts discharging.

That is, by turning off the power switch 8,
With this, the power-off detection circuit 4 starts the off-detection operation.

As a result, the discharge current flows to the control circuit 3, so the control circuit 3 operates to turn on the muting transistor 2, and maintains this state until the discharge current ends.

On the other hand, since the transistor TR1 is also turned off when the power switch 8 is turned off, the amplifier power supply circuit 5 to which DC has been supplied from the rectifier circuit A is also turned off at the same time, and the supply of power to the amplifier is stopped.

Therefore, the signal line 1 is dropped to the ground potential while the muting transistor 2 is on, so the signal output is stopped during this time, so-called muting is applied, and the output of the click sound is prevented. become.

[Problem that the invention seeks to solve]

By the way, the time during which the mute is applied is determined by the capacitance of the capacitor C□ of the power-off detection circuit 4, but in relation to the capacitance of the capacitor C2 provided for smoothing in the amplifier power supply circuit 5, It may become difficult to reliably prevent click sound output within the mute time.

In order to reliably prevent the output of click sounds, the capacitance of the capacitor should be selected to a value that satisfies the relationship 00≧C2, but since a large capacitance capacitor C□ must be prepared, the cost will increase. It will bring.

[Means for solving problems]

The present invention has been made in view of the above, and an object of the present invention is to eliminate the drawbacks of the prior art by using both a power-off detection capacitor and a smoothing capacitor.

In order to achieve this object, the present invention includes an output muting element for controlling a signal line, a switching element control circuit, a power supply circuit including a smoothing capacitor, and a power switch. When the power supply circuit is turned off, the switching element control circuit turns on the output muting switching element for a predetermined period of time by discharging the smoothing capacitor, thereby stopping signal output from the signal line during this time. Mute control circuit? provide. It is something.

[For production]

According to the configuration of the present invention, when the power switch is turned off and the power supply circuit is turned off, the smoothing capacitor that has been charged until then is discharged! In addition, since the discharge current flows only through the switching element control circuit, the output muting switching element can be turned on for a predetermined period of time by the control circuit until the discharge current ends, and the output signal of the signal line can be reliably muted. It can be used to prevent the output of click sounds.

〔Example〕

The implementation νG of the present invention will be described below with reference to the drawings.

FIG. 1 shows an output mute control circuit according to an embodiment of the present invention, and the same parts as in FIG. 2 are designated by the same numbers, and 03 to C
5 is a capacitor included in the button inside the amplifier power supply circuit 5, especially C
3 is a smoothing capacitor which also operates as a power off detection capacitor. TI(2 to TR6 are transistors.

In the above configuration, the power switch 8 is turned on at time 1□.
At the same time as the microcomputer power supply circuit 6 is turned off, the voltage E□ begins to drop, and the supply of power to the microcomputer is stopped. At the same time, transistors TR2 and TR3
turns off, transistor TR4 turns on, transistor TR6 turns off, and transistor TR5 turns on.
At this time t2, the voltage E2 of the amplifier power supply circuit 5 also begins to drop, and the supply of power to the amplifier is also stopped.

As a result, the smoothing capacitor C3 starts discharging the charge that had been charged up to that point, but the transistors TR5 and TR
6 are both off, their discharge current flows to the mute control circuit 3. As a result, the control circuit 3 operates to turn on the muting transistor 2, which functions as a switching element, and maintains this state until time t3 when the discharge current ends, and thereafter the discharge voltage (mute voltage) E3
starts to slump.

Therefore, microcomputer power supply voltage E1, amplifier power supply voltage E2
Among the mute voltages E3, the mute voltage E3 maintains its power supply voltage for the longest time after the power switch 8 is turned off, so even if a click sound occurs between t2 and t3, output can be reliably prevented. is not output to the signal line.

FIGS. 3(a) to 3(c) show the above E1. E2. 3 is a timing chart showing the change status of E3.

Incidentally, since the capacitors C4tC5 of the amplifier power supply circuit 5 are selected to have a smaller capacity than the smoothing capacitor, they are not affected by the mute operation as described above.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, by providing a single capacitor that serves both as a power-off detection capacitor and a smoothing capacitor in the power supply circuit, it is possible to reliably prevent the output of click sounds. Since this configuration eliminates the need to prepare an extra large-capacity capacitor, it is possible to reduce costs.

In the present embodiment, the muting switching element is constructed using a transistor, but the muting switching element is not limited to transistors, and any element having a muting function can be selected.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing a conventional example, and FIG. 3 is a timing chart for explaining the present invention. l...Signal line, transition for 2 rivers Miyuto, 3
...mute control circuit, 4... constant temperature off detection circuit,
5...Amplifier power supply circuit, 6...Microcomputer power supply circuit,
8...Power switch, T'R1-TR6...Transistor, C1-C5...Capacitor.

Claims (1)

[Claims] It includes an output mute switching element for controlling the signal line, a switching element control circuit, a power supply circuit including a smoothing capacitor, and a power switch. An output mute control circuit characterized in that the switching element control circuit turns on the output mute switching element for a predetermined period of time by discharging a capacitor, and stops signal output from the signal line during this period.