JPH0413789Y2 - - Google Patents

Description

[Detailed description of the invention] (a) Industrial application field The present invention relates to a muting circuit that suppresses noise generated when power is turned on and off when the power is turned on and off in connection with a tape recorder.

(b) Prior art A high-grade tape recorder called a tape deck is used by being connected to an amplifier with a high output, so the noise generated by the tape recorder is amplified by the amplifier and then emitted at a high level from the speaker. This will cause discomfort to the user. Some of the noise generated by tape recorders occurs when switching operations, but the level of noise generated when the power is turned on and off is particularly large, and a circuit called mutating, which suppresses such noise, is required. Various types have been developed. In such a muting circuit, the muting operation when the power is cut off generally uses the discharging current of the charge stored in the capacitor, but as the power supply voltage fluctuates, the charging voltage of the capacitor fluctuates, causing malfunctions. Something happened.

(c) Purpose of the invention The present invention aims to provide a muting circuit that not only suppresses the noise generated when the power is turned on and off, but also prevents malfunctions due to fluctuations in the power supply voltage.

(d) Structure of the invention The invention consists of a muting transistor whose collector-emitter path is connected between a signal transmission path and ground, and a device that operates in reverse when power is turned on and when the power is turned off, and conducts the said muting transistor for a predetermined period of time. a capacitor connected between a power supply path to the inverting circuit and ground, an output terminal of a rectifying and smoothing circuit that rectifies and smoothes an alternating current signal obtained from a commercial power supply into a direct current signal, and the capacitor connected to the A first diode and a Zener diode connected in series between the power supply terminal and the output terminal of a constant voltage circuit that converts the DC signal obtained from the rectifying and smoothing circuit into a predetermined voltage and the power supply terminal of the capacitor. and a second diode that is connected to the capacitor, such that the voltage applied to the power supply terminal of the capacitor through the second diode is higher than the voltage applied through the first diode and the Zener diode in a steady state. This is what I did.

(E) Embodiment The illustrated circuit is an embodiment of the muting circuit of the present invention. In the figure, 1 is a power supply terminal connected to a commercial power supply, 2 is a power switch that is closed when power is supplied, and 3 is a power transformer that is built in and converts an AC signal applied through the power switch 2 into a DC signal. A rectifying and smoothing circuit for rectifying and smoothing, 4 is a constant voltage circuit that adjusts the DC signal obtained from the rectifying and smoothing circuit 3 to a predetermined voltage, and has the function of supplying a constant voltage DC power to an amplifier circuit, etc. There is. In such a circuit configuration, the output voltage of the rectifying and smoothing circuit 3 rises faster than the output voltage of the constant voltage circuit 4 when the power is turned on, and falls faster when the power is turned off. Reference numeral 5 denotes a recording/playback switching switch that is switched by the recording/playback switching operation of the tape player, and has a common terminal C, a playback terminal P, and a recording terminal R. This is a so-called non-shooting type switch in which the switch S is not short-circuited by the switch S. The common terminal C of the recording/playback switch 5 is connected to the output terminal of the constant voltage circuit 4, and the playback side terminal P and the recording side terminal R are commonly connected and connected to the resistor 6.
and 7 to ground. 8 is a capacitor that is charged by the current from the constant voltage circuit 4 through the recording/playback switch 5, resistor 6 and diode 9 when the power is turned on, and when the power is turned on, the connection point A between the resistors 6 and 7 is connected to L( It has the effect of lowering the level (low). Reference numeral 10 denotes a diode that discharges the electric charge stored in the capacitor 8 when the power is cut off. 11 and 12 are Zener diodes and resistors connected in series between the output terminal of the rectifying and smoothing circuit 3 and the ground; 13 is a detection circuit that detects the voltage at the connection point B between the Zener diode 11 and the resistor 12; It is configured to output an L level signal to the output terminal 14 when the voltage at the connection point B drops below a predetermined value. An output terminal 14 of the detection circuit 13 is connected to a connection point A between the resistors 6 and 7 via a diode 15. 1
6 is an input terminal to which a playback signal is applied during a playback operation and a recording signal is applied during a recording operation;
Reference numeral 17 denotes a recording/playback amplifier circuit to which the playback signal or recording signal applied to the input terminal 16 is input and amplifies the signal. Reference numeral 18 receives the signal amplified by the recording/playback amplifier circuit 17. This is the output terminal. Reference numeral 19 denotes a muting transistor whose collector is connected to the signal transmission path 20 of the recording/playback amplifier circuit 17 and whose emitter is grounded. 21 has an input terminal connected to the connection point A between the resistors 6 and 7, and when the potential of the connection point A becomes L level, it performs an inverting operation, and outputs an H (high) level signal to its output terminal 22 for a predetermined period of time. This is an inverting circuit that outputs output terminal 2.
2 is connected to the base of the mutating transistor 19 via a Zener diode 23 and a resistor 24. 25 is the detection circuit 13
and capacitors 27 and 28 connected between the power supply path 26 to the inverting circuit 21 and the ground;
A first diode and a Zener diode 29 are connected in series between the power supply terminal of the constant voltage circuit 4 and the power supply terminal of the capacitor 25 .
In such a circuit, in a steady state, the voltage applied to the power supply terminal of the capacitor 25 via the second diode 29 is higher than the voltage applied via the first diode 27 and the Zener diode 28. The voltage value of the Zener diode 28 is set.

The muting circuit of the present invention is constructed as described above, and the operation of this circuit will now be described. The illustrated state is a non-power supply state,
When the power switch 2 is closed in this state, an AC signal is applied from the commercial power source to the rectifying and smoothing circuit 3, and the rectifying and smoothing circuit 3 outputs a rectified and smoothed DC signal. The DC signal output from the rectifying and smoothing circuit 3 is applied to a constant voltage circuit 4, and the voltage is made constant by the constant voltage circuit 4 and output. The output voltage of the constant voltage circuit 4 increases with a delay with respect to the increase in the output voltage of the rectifying and smoothing circuit 3. When a DC signal is output from the rectifying and smoothing circuit 3, a charging current flows to the capacitor 25 through the first diode 27 and the Zener diode 28, and the capacitor 25 is quickly charged. When the power switch 2 is closed and power is supplied, the capacitor 25 is immediately charged as described above, and power is supplied to the detection circuit 13 and the inversion circuit 21, so that the detection circuit 13 and the inversion circuit 21 are ready for operation. Become. Further, when a DC voltage is output from the constant voltage circuit 4, a charging current flows to the capacitor 8 through the recording/playback switch 5, the resistor 6, and the diode 9, and during this time, the connection point A, that is, the input terminal of the inverting circuit 21 goes to L level. Retained. As a result, the inversion circuit 21 is triggered and inverted to the operating state, and outputs an H level signal to the output terminal 22 for a predetermined period of time. The H level signal outputted to the output terminal 22 of the inverting circuit 21 is applied to the base of the muting transistor 19 through the Zener diode 23 and the resistor 24, and makes the muting transistor 19 conductive for a predetermined period of time. Therefore, the signal transmission path 20 is grounded by the mutating transistor 19, and signals such as noise caused by turning on the power are not outputted to the output terminal 18. Then, after a predetermined period of time has elapsed, the inverting circuit 21 returns to its original state, and the output of the output terminal 22 becomes L level, so that the muting transistor 19 is returned to its non-conducting state. When the power switch 2 is closed and power is supplied, the operations described above are performed, and after a predetermined period of time, each circuit enters a steady state. In such a steady state, the charging potential of the capacitor 25 is It is set by the voltage applied through diode 29. That is, the output terminal of the rectifying and smoothing circuit 3 and the capacitor 25
The first diode 27 and the Zener diode 28, which are connected between the power supply terminal and the power supply terminal, are in a non-conducting state. In addition, the capacitor 8 is charged to the H level, and the output terminal 1 of the detection circuit 13
4, an H level signal is output.
When a playback operation is performed in such a state, the tape recorder enters a playback operation state, and the playback signal played by the magnetic head is applied to the input terminal 16. The playback signal applied to the input terminal 16 is input to the recording/playback amplifier circuit 17, amplified, and then output to the output terminal 18. The reproduced signal outputted to the output terminal 18 is amplified by an amplifier having a large output, and then applied to a speaker to emit sound.

As described above, the muting operation and tape recorder playback operation are performed when the power is turned on, but
Next, the operation when performing a recording operation will be explained. When the user performs a recording operation, the switch S of the recording/playback switch 5 is switched from the playback terminal P to the recording terminal R, but during this switching,
The common terminal C is separated from the playback side terminal P and the recording side terminal R. When such a switching operation is performed, the input terminal of the inversion circuit 21 becomes L level, and the inversion circuit 21 is triggered and inverted to the operating state. When the inverting circuit 21 becomes operational, the muting transistor 19 becomes conductive for a predetermined period of time and performs the muting operation, as described above, so that the noise generated during switching is not applied to the magnetic head and is recorded on the magnetic tape. There isn't. When a tape recorder performs a recording operation, the above-described muting operation is performed for a predetermined period of time, and then the recording operation is started. If you perform an operation such as stopping while the tape recorder is in the recording mode, the switch S of the recording/playback switch 5 is switched from the recording side terminal R to the playback side terminal P. At the same time as switching to the state, the inverting circuit 2
1 is triggered and becomes operational. Since the muting operation by the muting transistor 19 is performed while the inverting circuit 21 is inverted to the operating state, noise accompanying the cancellation of the recording operation is not outputted to the output terminal 18. Such a muting operation is carried out in a steady state, but in a steady state, the stabilized voltage that is the output of the constant voltage circuit 4 is applied to the power supply terminal of the capacitor 25, so the power supply voltage may fluctuate somewhat. Even in this case, the voltage at the power supply terminal of the capacitor 25, that is, the voltage supplied to the inverting circuit 21 does not fluctuate, and the muting transistor 19 does not malfunction.

As described above, the muting operation is performed when the power is turned on and in the steady state.Next, the operation when the power is cut off by opening the power switch 2 will be explained. When the power switch 2 is opened, the output voltage of the rectifier and smoothing circuit 3 drops quickly, but the output voltage of the constant voltage circuit 4 drops with a delay. Further, since the electric charge stored in the capacitor 25 in the operating state is prevented from being discharged to the power supply circuit by the first diode 27 and the second diode 29, the discharged electric charge is transferred to the detection circuit 13 and the inverting circuit 21. Supplied as operating power. When the output voltage of the rectifying and smoothing circuit 3 drops as the power switch 2 is opened, a detection circuit 13 detects the voltage drop.
is detected and an L level signal is output to its output terminal 14. When an L level signal is output to the output terminal 14 of the detection circuit 13, the L level signal is applied to the input terminal of the inverting circuit 21, so that the inverting circuit 21 is triggered and becomes operational. When the inverting circuit 21 becomes operational, the muting transistor 19 becomes conductive for a predetermined period of time and performs the muting operation, as described above.
Noise caused by power cutoff is not output to the output terminal 18.

In this embodiment, the operation was explained in which the power was cut off and supplied by opening and closing the power switch 2, but it was also possible to turn off and supply power by the timer device while the power switch 2 was closed. Similar operations can be performed when controlling. Further, while the muting operation has been described in the case where power is supplied when the recording/reproduction changeover switch 5 is in the reproduction position, the same muting operation can also be performed when power is supplied when the recording/reproduction changeover switch 5 is in the recording position.

(f) Effects of the invention The muting circuit of the invention supplies operating power to an inverting circuit that conducts a muting transistor for a predetermined period of time when the power is turned on and when the power is turned off. Since this is done by the discharging current of the electric charge stored in the capacitor when the power is turned off, it is possible to reliably suppress the noise that occurs when the power is turned on and when the power is turned off. Then, when the power is cut off, the charging operation of the capacitor provided to supply operating power to the inverting circuit is performed by using the voltage supplied from the constant voltage circuit, which is higher than the voltage supplied from the rectifying and smoothing circuit in a steady state. I configured it to do so,
In other words, since the charging voltage of the capacitor is held constant in a steady state, it is possible to prevent the muting circuit from malfunctioning even if the voltage of the commercial power source changes and the output voltage of the rectifying and smoothing circuit changes. has very high practical value.

[Brief explanation of the drawing]

The illustrated circuit is one embodiment of the muting circuit of the present invention. Explanation of main figure numbers, 2... Power switch, 3...
Rectifying and smoothing circuit, 4... constant voltage circuit, 5... recording/playback switch, 13... detection circuit, 19... mutating transistor, 20... signal transmission line, 21... inverting circuit, 25... capacitor, 27...first diode, 28...zener diode, 29...second diode.

Claims (1)

[Scope of utility model registration request] In a tape recorder equipped with a rectifying and smoothing circuit that rectifies and smoothes an AC signal obtained from a commercial power source into a DC signal, and a constant voltage circuit that adjusts the DC signal obtained from the rectifying and smoothing circuit to a predetermined voltage, a a mutating transistor to which a collector-emitter path is connected; an inverting circuit that performs an inverting operation for a predetermined period of time when the power is turned on and when the power is turned off, and keeps the mutating transistor in a conductive state during that time; and a power supply path to the inverting circuit. a capacitor connected between the ground and supplying operating power to the inverting circuit when the power is turned off; and a capacitor connected in series with each other between the output terminal of the rectifying and smoothing circuit and the power supply terminal of the capacitor when the power is turned on. a first diode and a Zener diode that supply charging current to the capacitor to instantaneously charge the capacitor and supply operating power to the inversion circuit; and an output terminal of the constant voltage circuit and a power supply terminal of the capacitor. and a second diode connected between the two and supplying a charging current to the capacitor when in a steady state, and the voltage applied from the constant voltage circuit to the power supply terminal of the capacitor via the second diode. A muting circuit for a tape recorder, characterized in that the voltage is higher than the voltage applied by the rectifying and smoothing circuit to the power supply terminal of the capacitor via the first diode and the Zener diode.