JPH0256862B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates to a device for driving muting to remove noise generated when power is turned on or off in audio equipment or the like.

Conventional configurations and their problems Audio equipment often generates unpleasant noise in its output when it is turned on and off. In order to eliminate this, a muting circuit is often used in which a relay is provided at the output, the output signal is passed after a certain period of time after the power is turned on, and the output signal is immediately cut off when the power is turned off.

Figure 1 shows a circuit diagram of a conventional example of a device for driving a mutating relay for the above purpose, in which 1 is a winding of a power transformer, 2 is a rectifier diode, 3 is a smoothing capacitor, and 4 is a resistor. ,
5 is a diode; 6 and 7 are capacitors and resistors forming an integrating circuit for determining the muting operation time when the power is turned off; 8 is a transistor;
9 and 10 are capacitors and resistors forming an integrating circuit for determining the muting operation time when the power is turned on; 11 is a relay driving transistor;
12 is a winding coil of the relay. Further, A and B indicate nodes.

The operation of the conventional muting drive device configured as described above will be described below.

First, when the power is turned on, an alternating voltage is generated at one end A of the winding 1 of the transformer, which is applied to the diode 5.
A negative current is supplied to one end B of the capacitor 6. On the other hand, the voltage at A is rectified by diode 2, and a positive voltage is generated at one end of capacitor 3.
A positive current is supplied to point B through resistor 7.
Here, if the resistor 4 is set to a somewhat lower value than the resistor 7, the base of the transistor 8 will be reverse biased and the transistor 8 will be cut off.

On the other hand, one end of the capacitor 9 is charged to a positive voltage by the resistor 10, and after a certain period of time, the voltage reaches V _BE of the transistor 11 and the transistor 1
1 becomes conductive, relay 12 is driven, and muting is released.

Next, the operation when the power is turned off will be explained using the waveform diagram shown in FIG.

In FIG. 2, a shows the voltage waveform at point A, and b shows the voltage waveform at point B, showing the case where the power is turned off at time _t1 .

If the capacitance of capacitor 3 is set sufficiently large, resistor 7 will continue to supply current to point B for a while even after the power is turned off, so that at time t ₁ as shown in FIG.
After turning off the power at , the voltage b at point B continues to rise and reaches V _BE of transistor 8 at time t ₂ .
Transistor 8 conducts, transistor 11 is cut off, relay 12 is turned off, and muting is activated.

By the way, after turning off the power at t ₁ , the voltage b becomes
If the time until time t ₂ at which V _BE is reached is too long, the noise generated when the power is turned off will not be blocked and will be output, so it is desirable to make it as short as possible. In order to shorten this time, the capacitor 6 may be made smaller or the resistor 7 may be made lower, but this will increase the ripple of the voltage b. While the power is on, the positive peak value of the ripple of voltage b is absolutely constant, regardless of component variations or AC power frequency.
V _BE must not be reached, so if we look at the margin, the values of capacitor 6 and resistor 7 cannot be made too small, and there is a limit. Therefore, it is not possible to make muting work in a sufficiently short time after the power is turned off. There was a problem.

Purpose of the invention The present invention solves the above-mentioned conventional problems.
It is an object of the present invention to provide a mutating drive device that can immediately operate mutating when the power is turned off.

Structure of the Invention The present invention provides a mutating drive including a transistor for shunting a capacitor, a base resistor thereof, diodes connected between the base and emitter and between the base and collector of the transistor, and means for charging the capacitor. This device shunts the capacitor during both half cycles of alternating current, thereby preventing malfunctions and shortening the muting operation time when the power is turned off.

DESCRIPTION OF THE EMBODIMENTS FIG. 3 shows a circuit diagram of a muting drive device in an embodiment of the present invention. In FIG. 3, 1 to 12 are the same as those with the same numbers in FIG. 1, 13 is a diode, and 14 is a transistor.

The operation of the mutating drive device of the embodiment configured as described above will be explained below.

First, since the operation when the power is turned on is exactly the same as that shown in FIG. 1, a description thereof will be omitted.

The waveforms at points A and B when the power is turned off are shown in a and b in FIG.

First, during the positive half cycle period a, a forward current is supplied from the resistor 4 to the base of the transistor 14, so the transistor 14 becomes conductive and the voltage at point B is shunted to the reference point. At this time, diodes 5 and 13 are cut off.

Next, in the negative half cycle of a, the voltage on the diode side of the resistor 4 is clamped to the reference point -V _D by the diode 13. Then, the voltage at point B is maintained at a voltage that has increased to the + side by the voltage of diode 5 from there, that is, approximately the voltage at the reference point.
At this time, transistor 14 is cut off.

Then, near the zero clock of a, both the transistor 14 and the diodes 5 and 13 are cut off, so the voltage at point B increases with a slope on the positive side due to the current from the resistor 7.

The above situation is shown by the waveform up to time _t1 in FIG.

Then, when the power is turned off at time _t1 , the voltage at point B rises with the above slope, and when it reaches V _BE of transistor 8 at time _t2 , transistor 8 becomes conductive and transistor 11 is cut off. Relay 12 is turned off and muting is activated.

By the way, in this embodiment, the slope of point B when the power is turned off can be set to be much steeper than in the conventional example shown in FIG. The reason is,
The slope in the case of FIG. 1 must be such that the peak value of voltage b does not reach V _BE during approximately the positive half cycle period of a, whereas in the embodiment of FIG.
The voltage b increases only during a very short period near the zero crossing of
This is because it is sufficient to prevent the peak value of from reaching V _BE .

Therefore, in this embodiment, muting can be performed in an extremely short time when the power is turned off.

In the embodiment shown in FIG. 3, NPN type transistors were used for the transistors 14, 8, and 11.
The same thing applies when these are replaced with PNP type ones and the directions of diodes 2, 5, and 13 are reversed. Also when the transistor 11 is replaced with a comparator or the relay 12 is replaced with other muting means. It is valid. Furthermore, the rectifier circuit 2,
3 with another independent power supply, or resistor 7 or 1.
It goes without saying that the present invention is effective even when 0 is replaced with other current supply means.

Effects of the Invention According to the present invention, an excellent muting drive device is realized that can obtain the effect of shortening the muting operation time when the power is turned off while preventing malfunctions while the power is turned on. It is possible.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional mutating drive device, FIG. 2 is a voltage waveform diagram for explaining the operation of FIG. 1, and FIG. 3 is a circuit diagram of a mutating drive device in an embodiment of the present invention. FIG. 4 is a voltage waveform diagram for explaining the operation of FIG. 3. 4...Resistor, 5, 13...Diode, 14...
...transistor, 6...capacitor, 7...current supply means.

Claims (1)

[Claims] 1 A resistor whose one end is connected to one end of an AC power supply,
A transistor whose base is connected to the other end of the resistor and whose emitter is connected to a reference point, and a transistor with a polarity opposite to the base-emitter junction and base-collector junction, respectively, is connected between the base-emitter and base-collector of the transistor. A mutating drive characterized by comprising a first diode and a second diode connected in a relationship, a capacitor connected between the collector and emitter of the transistor, and means for charging the capacitor. Device.