JPS5824257Y2 - Muting circuit - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a muting circuit for tape recorders and the like.

Figure 1 shows a conventional circuit, where 1 and 2 are lamps for meter lighting, 3 is a power transformer, 4 is a rectifier diode, and 5
is the ripple filter capacitor, 6 is the motor, 7,
8 is a resistor and a capacitor that constitute a time constant circuit that determines the time to release muting after power is turned on; 9 is a diode that serves as a discharge path for capacitor 8; 10, 11
is a resistor that supplies a signal to the base of the current amplifying transistor 12, 13 is a collector resistor of the transistor 12, and 14 is a resistor that supplies a signal to the base of the current amplifying transistor 12;
is a diode that separates the power supply of the motor 6 and the transistor 12 after the power is turned off, 151/'i is a capacitor that stores charge for a certain period of time after the power is turned off, 16 is a Zener diode for waveform shaping, and 17 is a muting circuit whose collector is connected to the signal line 19. This is the base resistance of the transistor 18 that applies the voltage.

In the above circuit, when the power is turned on, the alternating current transformed by the power transformer 3 is rectified by the rectifying diode 4 and stored in the capacitor 5.

Furthermore, the capacitor 15 is also charged through the diode 14 and immediately reaches the power supply voltage.

The base potential of the transistor 12 is the resistor 7 and the capacitor 8.
It rises slowly with the time constant of .

Therefore, since the transistor 12 is in a cut-off state for the time determined by the above-mentioned time constant, the collector resistor 13 of the transistor 12, the waveform shaping Zener diode 16, and the resistor 17 are connected to the base of the transistor 18 during that time.
A base current is supplied through the transistor 18, and the transistor 18 becomes conductive, and the signal line 19 is grounded through a low impedance, and muting is applied.

Furthermore, when the power is turned off, the capacitor 5 is discharged by the motor 6 and its voltage quickly drops.

Since the capacitor 8 is also discharged by the motor 6 through the diode 9, the base voltage of the transistor 12 decreases, and the transistor 12 becomes cut off.

Since the capacitor 15 is a diode 14, it is not discharged through the motor 6, and the collector resistor 13 of the transistor 12
, the Zener diode 16, and the resistor 17 as the base current of the transistor 18.

Therefore, the transistor 18 becomes conductive immediately after the power is turned off, and the signal line 19 is grounded with low impedance, thereby causing muting.

However, in the above circuit, due to the back electromotive force of the motor 6 and the large capacity of the capacitor 5, the capacitor 8 does not actually discharge immediately after the power is turned off, and click noise occurs when the power is turned off. is not completely erased by muting and some time remains,
The noise generation time was made as short as possible by the ratio of resistors 10 and 11.

The present invention attempts to eliminate the above-mentioned drawbacks of the conventional ones.

Therefore, the present invention is constructed as shown in FIG. 2, where 1 to 19 are the same or equivalent parts as in FIG. 1, and 20 is a ripple filter with a smaller capacity than the capacitor 5. The capacitor 21 is a diode that separates the power rectifier diode 4 and the motor 6 when the power is turned off.The difference from the conventional circuit shown in Fig. 1 is that the lamp 1.2 for meter illumination, etc. A diode 21 whose anode is connected to the power rectifying diode 4 is interposed between the power rectifying diode 4 and the capacitor 5 and the motor 6, and the cathode of the diode 9 is connected directly between the power rectifying diode 4 and the ground. It is connected to the anode.

In the circuit with the above configuration according to the present invention, the operation when the power is turned on is the same as that in the circuit shown in FIG. Moreover, since capacitor 20 has a relatively small capacity, discharging capacitor 8 is equivalent to opening the power supply! They are completed at the same time, so muting takes effect more quickly.

Note that the meter illumination lamps 1 and 2 can be replaced with other elements, and the ripple filter capacitor 20 is not indispensable.

As is clear from the above, the present invention can prevent delays in muting when the power is disconnected by connecting the base circuit of the driving transistor of the muting transistor to a circuit that discharges quickly. be.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional example, and FIG. 2 is a circuit diagram of an embodiment of the present invention. 1.2...Lamp for meter illumination, 3...Power transformer, 4...Power rectifier diode, 9, 14, 21.
...Diode, 5,8,15,20...Capacitor, 6...Motor, 7,10,11.13,17...
Resistor, 12.18...Transistor, 16...Zener diode, 19...Signal line.

Claims (1)

[Scope of utility model registration request] Elements such as meter lighting lamps connected between the power rectifier diode and ground, a first capacitor connected in parallel with this as necessary, and a first diode whose anode is connected to the power rectifier diode. , a second capacitor with a larger capacity than the first capacitor connected between the cathode of the first diode and the ground, a motor connected in parallel with the second capacitor, and a second capacitor connected between the cathode of the first diode and the ground. a second diode with its anode connected, a third capacitor connected between the cathode of the second diode and ground, a third diode with its cathode connected to the power rectifier diode, in parallel with the third diode a fourth capacitor connected between the anode of the third diode and ground; a fourth capacitor whose base is connected to the anode of the third diode through the resistor and whose emitter is grounded; a second resistor connected between the collector of the first transistor and the cathode of the second diode; the base is connected to the collector of the first transistor via a resistor, a diode, etc.; A muting circuit in a tape recorder, etc., consisting of a second transistor connected to a signal line and whose emitter is grounded.