JPH024498Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to the improvement of a muting circuit,
In particular, it is an object of the present invention to provide a muting circuit suitable for performing muting at a plurality of different times.

In audio equipment, a muting circuit is provided to prevent noise from being generated when various switches are switched. FIG. 1 shows an example of this, in which a signal amplification system consisting of a preamplifier 1, a volume 2, a main amplifier 3, and a speaker 4 is connected to
The emitter path is shaft-connected, and by applying a control signal from a muting signal generator 6 to the base of the muting transistor 5, muting is performed to prevent noise generation. The muting signal generator 6 operates in conjunction with, for example, a first switch 7 that operates in conjunction with a power switch, a second switch 8 that operates in conjunction with a function changeover switch, and a band changeover switch of a tuner. The control signal is generated in response to the operation of the three switches including the third switch 9 which is activated. Incidentally, the duration of noise generated when the power switch, function changeover switch, or band changeover switch is operated varies widely. Therefore,
In order to prevent the noise from occurring, muting must be performed in accordance with the duration of the noise. Conventionally, however, circuits corresponding to the three switches were provided independently as the muting signal generating section to drive the muting transistor 5, which resulted in a disadvantage that the circuit configuration became complicated and the cost increased. It had

The present invention has been developed in view of the above points, and will be described below based on embodiments with reference to the drawings. FIG. 2 shows an embodiment of the present invention, in which reference numeral 10 denotes a normally closed first switch 11 that is turned on and off in conjunction with the power switch in the opposite direction, and a first switch 11 connected in parallel to the first switch 11. 1 capacitor 12 and a first resistor 13 for charging the first capacitor 12; 14 is a second switch 15 that is momentarily turned on in response to operation of a function changeover switch; a second capacitor 16 connected in parallel to the second switch 15; and a second capacitor 16 connected in parallel to the second switch 15.
A second time constant circuit 18 is connected in parallel to a third switch 19 which is momentarily turned on in response to the operation of the band changeover switch. A third time constant circuit 22 includes a third capacitor 20 and a third resistor 21 for charging the third capacitor 20.
A PNP type drive transistor, 23 is a first isolation diode whose cathode is connected to the first time constant circuit 10 and an anode is connected to the base of the drive transistor 22 via a resistor 24; 25 is a cathode connected to the second time constant circuit 14; , a second isolation diode whose anode is connected to the anode of the first isolation diode 23; 26 has a cathode connected to the third time constant circuit 18 ;
a third isolation diode whose anode is connected to the anode of the first isolation diode 23; and 27 a muting transistor driven by the drive transistor 22;

Next, the operation will be explained. First, before the power is turned on, no power supply voltage is applied to the power supply terminal 28, and the first, second, and third capacitors 1
2, 16 and 20 are in a fully discharged state. When the power switch is turned on in this state, the emitter voltage of the drive transistor 22 rises, the drive transistor 22 is immediately turned on, and the muting transistor 27 is accordingly turned on to start mutating. At that time, the first switch 11
is turned off by turning on the power switch, so charging of the first capacitor 12 starts immediately after the first switch 11 is turned off.
Further, the second and third capacitors 16 and 20 are
Charging begins immediately after the power switch is turned on. Generally, the period of noise generation when the power is turned on is long, whereas the period of noise generation when switching functions is short, and the period of noise generation when switching bands is even shorter. Therefore,
First, second and third capacitors 12, 16 and 2
The charging time constant of 0 has different values depending on the noise generation period. The first, second and third time constant circuits 10 , 14 and 18 are connected in parallel to the drive transistor 22, and
Second and third isolation diodes 23, 25 and 26
Even if the second capacitor 16 and the third capacitor 20, which have short charging time constants, are completely charged,
The driving transistor 22 and muting transistor 27 continue to be turned on until the charging of the first capacitor 12 is completed.

However, as time passes, the first capacitor 12
When the charging progresses and the terminal voltage of the first capacitor 12 reaches a predetermined level L, the first isolation diode 23 and the drive transistor 22 are turned off, and the muting transistor 27 is also turned off accordingly, and the muting is canceled. , the signal will pass through the signal path. Figure 3A shows the terminal voltage of the first capacitor 12, and shows that the power switch is turned on at time _t1 and the terminal voltage rises to a predetermined level L at which the drive transistor is turned on at time _t2 . ing. Therefore, the base voltage of the muting transistor 27 becomes as shown in FIG. 3B, and a relatively long muting period _T1 can be obtained.

In the steady state, the first, second, and third capacitors 12, 16, and 20 are fully charged, and the driving transistor 22 and muting transistor 27 remain off. If the function changeover switch is operated at time _t3 , the second switch 15 is turned on instantaneously, and the charge in the second capacitor 16 is instantaneously discharged. Therefore, at the same time as the function changeover switch is operated, the drive transistor 22 and the muting transistor 27 are turned on to enter the muting state. Since the second switch 15 is turned off immediately after being turned on, charging of the second capacitor 16 by the second resistor 17 starts from that point. When the charging of the second capacitor 16 progresses and its terminal voltage reaches a predetermined level L at time _t4 , the drive transistor 22 and the mutating transistor 27 are turned off and mutating is completed. 3C shows the terminal voltage of the second capacitor 16, and FIG. 3D shows the base voltage of the muting transistor 27.
As is clear from the figure, the muting period is T ₂
becomes.

When operating the band selector switch, the third
The switch 19 is activated and a muting period _T3 determined by the time constant of the third time constant circuit 18 can be obtained, but its operation is the same as the operation of the function changeover switch, so a description thereof will be omitted.

As described above, according to the present invention, the first time constant circuit is used to set the muting period when the power is turned on, and the second time constant circuit is used to set the muting period when switching operations other than when the power is turned on. a time constant circuit is provided independently, and the first
Since a single drive transistor is controlled by the second time constant circuit, there is an advantage that a muting circuit that can independently set each muting period can be provided with a simplified circuit configuration. Further, according to the present invention, when the power switch is turned on, the first switch is closed to discharge the capacitor of the first time constant circuit, and when the power switch is turned on, the capacitor is discharged. Since it is designed to discharge
This has the advantage that even if the power switch is operated repeatedly in a short period of time, muting is reliably performed as set. Further, according to the present invention, a separation diode is provided to connect the time constant circuit and the drive transistor, and the separation diode has the first function of preventing interference between the time constant circuits; The second step is setting the threshold level.
This function has the advantage of providing an accurate muting circuit that does not malfunction.

In the embodiment of the present invention, a case has been described in which three time constant circuits are used for three muting applications, but the present invention is not limited to this and can be used for many more applications. It is something.

[Brief explanation of the drawing]

FIG. 1 is a circuit block diagram showing a conventional example of a muting circuit, FIG. 2 is a circuit diagram showing an embodiment of the present invention, and FIGS. 3A to 3D show characteristics for explaining the present invention. It is a diagram. Explanation of main figure numbers, 10 , 14 , 18 ...Time constant circuit, 22...Drive transistor, 23, 25,
26...Isolation diode.

Claims (1)

[Scope of utility model registration request] A muting circuit for performing muting during operation of a power switch and other changeover switches, comprising a muting transistor that blocks a signal passing through a signal path, and a drive transistor that drives the muting transistor.
A normally closed first switch that opens and closes in conjunction with the power switch in the opposite direction, and discharges when the first switch is closed and starts charging when the first switch opens. a first time constant circuit consisting of a first capacitor and a first resistor that sets a charging time constant of the first capacitor in consideration of the first capacitor; a second switch that is momentarily closed, a second capacitor that is discharged when the second switch is closed and starts charging when the second switch is open; and a second resistor that sets a charging time constant of the second capacitor in consideration of the second capacitor, and the charging time constant of the second capacitor is smaller than the charging time constant of the first capacitor. the first and second time constant circuits are connected in parallel to the base of the driving transistor via isolation diodes, and the first time constant circuit A muting circuit, characterized in that a muting period is set when the power is turned on, and the second time constant circuit is used to set a muting period when an operation is switched other than when the power is turned on.