JPH024497Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a muting circuit that uses the same time constant circuit to apply muting not only when the original muting signal is input, but also when the power switch is turned on and off.

Traditionally, in synthesizer tuners,
Various muting circuits already exist that apply muting to cut off audio output not only when the original mute signal is input when switching preset memories or switching bands, but also when the power switch is turned on and off. . However, both had complicated circuit configurations and were expensive.

The present invention was developed to solve these conventional problems, and uses the same time constant circuit to apply muting not only when the original mute signal is input, but also when the power switch is turned on and off. In addition, the muting time when the power switch is turned on and off can be set to be longer than the muting time when the muting signal is input.

An embodiment of the present invention will be described below with reference to FIG.

Reference numeral 1 denotes an AC commercial power source, which is coupled to a primary winding 4 of a transformer 3 via a power switch 2. This transformer 3 has two secondary windings 5 and 6,
One secondary winding 5 is connected to a +B power output terminal 10 to, for example, a synthesizer tuner via a full-wave rectifier 7, a smoothing capacitor 8, and a voltage stabilization circuit 9. Coupled to circuit 12. This muting circuit 12 is turned on after a certain period of time after the power switch 2 is turned on, and a first switching circuit 13 is turned off suddenly after the power switch 2 is turned off.
It consists of a time constant circuit 14 that charges and discharges at different time constants depending on the off state and a mute signal to be described later, and a second switching circuit 15 that is controlled on and off by the output of this time constant circuit 14 to cut off audio output.

The first switching circuit 13 includes the other secondary winding 6 of the transformer 3, a diode 16, a resistor 17, a charging/discharging capacitor 18 and a resistor 19, a resistor 20, and a transistor 21.

The second switching circuit 15 includes a control transistor 22, a main transistor 23, two transistors 24 and 25, and four resistors 2.
6, 27, 28, 29, and the emitters of the transistors 24 and 25 are connected to the audio input terminal 3.
0 and 31 via resistors 32 and 33, and directly connected to audio output terminals 34 and 35, and the collector is grounded.

The time constant circuit 14 includes one capacitor 36 for charging and discharging, one diode 37, and four first, second, third, and fourth resistors 38, 39, 40, 4.
1, and a mute signal input terminal 42 is connected to a diode 43 at the connection point between the third and fourth resistors 40 and 41.
are connected via. Of these, the second resistor 3
9 mainly contributes to setting the muting time when the power is turned on, and the third resistor 40 mainly contributes to setting the discharging time when the muting signal is input. It is assumed that a pulse signal is applied to the mute signal input terminal 42 from the IC of the synthesizer tuner as a mute signal at the time of preset memory switching and/or band switching. In addition, 44
is a capacitor that slows down the voltage change when the power is turned off.

Next, the operation of the circuit according to the present invention will be explained based on FIG.

When the power switch 2 is turned on at time _t1 , the transistor 21 is turned off because the capacitor 18 of the first switching circuit 13 has not yet been sufficiently charged. Therefore, almost at the same time as the power switch 2 is turned on, the resistor 38, the diode 38, and the resistor 4 are turned on.
A base current is caused to flow through the control transistor 22 of the second switching circuit 15 through the transistors 0 and 41, turning on the control transistor 22, and further turning on the main transistor 23. When the main transistor 23 is turned on, the transistors 24 and 25 are also turned on, and the audio input terminals 30 and 31 are grounded.
The audio signal is not sent to the output terminals 34, 35 and is in a muting state.

The capacitor 18 gradually charges and the transistor 21 turns on, for example at time _t2 , about 1.5 seconds later.
When the transistor 21 is turned on, the resistor 38 is grounded, but instead of the current flowing through the resistor 38, the charging current of the capacitor 36 flows to the base of the control transistor 22, and the transistor 22 continues to be on. Transistors 23, 24,
25 also remains on and continues to mute.

When capacitor 36 completes charging at time _t3 , transistor 22 is turned off, so transistor 2
3, 24, and 25 are also turned off, mutating is canceled, and the audio signal is output to the output terminals 34, 35.
sent to. Muting time at this time T ₁
is t ₁ which is the time from t ₁ to t ₂ plus the charging time of the capacitor 36 (C ₃₆ × [R ₃₉ (R ₄₀ + R ₄₁ )])
to t ₃ .

Next, at _t4 , assuming that the preset memory or band has been switched in the tuner, the mute signal is transferred to the input terminal 42.
Enter from. If the pulse voltage of this mute signal is V and the pulse width is T ₂ (for example, 0.5 seconds), then T ₂
>C ₃₆ × R ₄₀ , the voltage V ₃₆ across the capacitor 36 is V × R ₃₉ / (R ₃₉ + R ₄₀ )
only decreases. That is, the capacitor 36 is discharged by this voltage _V36 during the period of the pulse signal _T2 .
During this discharge time _T2 , the pulse signal is applied to the resistor 41.
Since it is also supplied to the transistor 22 via
Transistor 22 is also on. When the pulse signal disappears at t ₅ , the charging current flows through the capacitor 36 to the resistors 39, 40, and 41 again, the transistor 22 continues to be turned on, and at t ₆ , the charging current flows through the resistors 39, 40, and 41, and the capacitor 3
Muting continues until charging of 6 is completed. At this time, the muting time T ₃ from t ₄ to t ₆ consists of the capacitor 36 and the resistors 39, 40, 4
Defined by a value of 1.

Next, when power switch 2 is opened at t ₇ , the first
The capacitor 18 of the switching circuit 13 is rapidly discharged at a time _T4 due to the time constant of the resistor 19.
Here, when the power supply frequency is 50Hz, transistor 2
Set the time constant so that 1 turns off within 15 to 20 msec. When this transistor 21 is turned off at time _t8 , discharged charges from the capacitor 44 and the tuner flow through the resistors 38, 40, and 41, turning on the transistor 22 at time _t8 , and further turning on the transistor 22.
Since signals 3, 24, and 25 are turned on, muting starts at _t8 . At the same time, the voltage across capacitor 36 drops to the voltage across resistor 38. When the time for a human to turn on and off the power switch 2 is T ₅ , if C ₃₆ × R ₃₈ < T ₅ and R ₃₈ ≪ R ₃₉ and R ₃₈ ≪ (R ₄₀ + R ₄₁ ) are set, then
Even if the power switch 2 is turned on and off several times, the muting time hardly changes. Since the capacitor 44 continues to discharge even after t8 _hours when muting has started, the discharged charge at that time keeps the transistor 22 in the on state. Note that without the diode 11, the capacitor 44 would also discharge to the tuner terminal 10, causing a sudden voltage change, which would cause a DC level shift at the audio output terminals 34, 35 when muting is released, causing a hop sound. Cause. Therefore, diode 1
1 is inserted to prevent backflow to the tuner terminal 10, and rather allows a discharge current to flow from the tuner side, thereby slowing down the voltage change of the capacitor 44. Then, at time _t9 , when the control transistor 22 is turned off, the transistors 23, 24,
25 is also turned off one after another to stop the mutating.

Since the present invention is constructed as described above, sufficient muting is applied particularly when the power switch is turned on and off, and noise when the power switch is turned on and off can be sufficiently eliminated. Further, even if the power switch is turned on and off repeatedly in a short period of time, the muting time hardly changes because the capacitor is discharged each time. Moreover, it is also possible to easily set the muting time when the power switch is turned on and off to be longer than the muting time using the muting signal. Furthermore, the circuit can be easily constructed.

[Brief explanation of the drawing]

FIG. 1 is an electric circuit diagram showing an embodiment of a muting circuit according to the present invention, and FIG. 2 is an output waveform diagram of each part. 2...Power switch, 13...First switching circuit, 14...Time constant circuit, 15...Second switching circuit, 18...Capacitor, 19...
...Resistor, 21...Transistor, 22...Control transistor, 23...Main transistor, 24,2
5...Transistor, 30, 31...Audio input terminal, 34,35...Audio output terminal,
36... Capacitor, 37... Diode, 3
8, 39, 40, 41...first, second, third, fourth resistor, 42...mute signal input terminal.

Claims (1)

[Scope of utility model registration claim] When the power switch is turned on, the battery is charged for a specified period of time,
The first switching circuit consists of a charging/discharging circuit that rapidly discharges through a resistor when off, a transistor that is controlled to turn on and off by this charging/discharging circuit, one capacitor, four resistors, and one diode. , a capacitor and a second resistor are inserted in series between the power supply and the ground, a series circuit of the first resistor and a diode is connected in parallel with the capacitor, and a first switching circuit is connected to the connection point of the first resistor and the diode. A second switching circuit is connected to the connection point between the capacitor and the second resistor via a series circuit of third and fourth resistors, and a mute input terminal is connected to the connection point between the third and fourth resistors. a control transistor that is controlled on and off by the output of the time constant circuit, a main transistor that is controlled on and off by this control transistor, and an audio signal that is controlled on and off by this main transistor. 1. A muting circuit comprising: a second switching circuit comprising a transistor that couples an input terminal to either ground or an output terminal.