JPH039378Y2 - - Google Patents

Description

[Detailed Description of the Invention] <<Industrial Application Field>> The present invention relates to a muting circuit in audio equipment, and is particularly intended to block noise generated from amplifiers and the like due to a drop in power supply voltage due to power cut-off, etc.

<Prior Art> In audio equipment that is powered only by a power line via a power switch, during a muting operation performed in response to a drop in the power supply voltage, the muting transistor is activated by supplying power from the power line. It is impossible to drive the drive transistor to Therefore, a capacitor is provided that is connected to the power line and charged when the current is applied, and the discharge current of this capacitor drives the drive transistor for a certain period of time when the power is cut off, and the muting transistor shorts the signal line and the ground. was.

<<Problems to be Solved by the Invention>> However, unless the capacitance of the capacitor is increased, the muting transistor cannot be sufficiently driven, resulting in high costs, and the muting operation cannot be performed reliably.

<Means for Solving the Problem> A first power line that supplies current to a desired circuit via a power switch; a second power line that supplies current to a desired circuit without going through a power switch; a muting transistor that short-circuits the signal line and the ground; a drive transistor whose collector current is supplied from a second power supply line to drive the mutating transistor; and a drive transistor which is connected to the first power supply line and is charged. In order to control the active time of the drive transistor during discharging, there is a capacitor connected to the base of the drive transistor, and a capacitor connected to the base of the drive transistor that detects when the voltage of the first power supply line falls below a predetermined level. and a voltage detection circuit that controls the drive transistor.

<<Operation>> When the voltage of the first power supply line is equal to or higher than a predetermined level, the base potential of the drive transistor is set to the first state by the voltage detection circuit in order to deactivate the drive transistor during non-mutating.
When the voltage detection circuit sets the base potential of the drive transistor to a second state due to a power cutoff or a drop in the power supply voltage, the drive transistor is activated for a period determined by the discharge of the capacitor;
The muting transistor is driven by the collector current supplied from the second power supply line.

<<Embodiment>> The figure shows a block diagram of an embodiment in which the circuit of the present invention is incorporated into a tape recorder.

The muting control circuit 1 opens its output terminal 2 when a muting operation is performed, for example, a stop mode, is selected, and sets the output terminal 2 to a grounded state when a muting operation is not performed, for example, a play mode. This output terminal 2
is connected to the emitter of the transistor Tr ₁ and to one end of the resistor R ₁ . The base of the transistor Tr ₁ is connected to the other end of the resistor R ₁ and also to one end of the resistor R ₂ . The anode of the Zener diode _D1 is connected to the other end of the resistor _R2 , and its cathode is connected to a first power supply line L that supplies current from a power supply E with a voltage value _V0 to a signal amplifier, etc., via a power switch SW. Connected to ₁ . Here the transistor Tr ₁ and the resistor
R ₁ , R ₂ and the Zener diode D ₁ constitute a voltage detection circuit 3, and when the resistors R ₁ and R ₂ are set to the same resistance value, the base potential Vb of the transistor Tr ₁ is Vb when the output terminal 2 is in the grounded state. = V ₀ − Vz / 2 (Here, Vz indicates the Zener voltage) When the voltage value V ₀ of the power supply line L ₁ drops to the minimum guaranteed voltage at which the signal amplifier etc. can operate without generating noise. _The resistor _{R 1 ,}
R ₂ and a Zener diode D ₁ are selected.

The first power supply line _L1 is further connected to the anode of a backflow prevention diode _D2 , whose cathode is connected to the other end of a capacitor C whose one end is connected to ground. Further, the connection point between the diode _D2 and the capacitor C is connected to the base of the drive transistor _Tr2 via a resistor _R3 . Here, the capacitor C and the resistor _R3 constitute a time constant circuit 4.
The collector of transistor Tr ₂ is the power switch SW
It is connected to a second power supply line _L2 that supplies current to a time display circuit of a tape recorder, for example, without going through the power supply line L2. Further resistor R ₃ and drive transistor Tr ₂
The collector of the transistor Tr 1 is connected to the connection point of the base of the transistor Tr ₁ .

The emitter of the drive transistor Tr ₂ is connected between the signal line Ls and the ground via a resistor R ₄ , its collector
The emitter is connected to the base of the mutating transistor Tr ₃ , so that the driving transistor Tr ₂ controls the muting transistor Tr ₃ .

In the above configuration, when the open power switch SW is closed, the tape recorder enters the initial state of stop mode. At this time, the output terminal 2 of the muting control circuit 1 is in an open state, so the base of the drive transistor Tr ₂ is connected to the resistor.
By applying voltage E through R ₃ , diode D ₂ , and power supply line L ₁ , the drive transistor
Tr ₂ becomes active and drives the muting transistor Tr ₃ by the collector current supplied from the power supply line L ₂ . Capacitor C is also rapidly charged via diode _D2 .

For example, when the play mode is selected, the output terminal 2 becomes grounded, but the base potential of the voltage detection circuit 3 of the transistor Tr ₁ rises due to the previous closing of the power switch SW, and the voltage of the drive transistor Tr ₂ increases. The base and the output terminal 2 of the muting control circuit 1 are short-circuited. Therefore, when the base of the drive transistor Tr ₂ becomes the ground potential, the drive transistor Tr ₂ becomes inactive and blocks the operation of the muting transistor Tr ₃ .

Also, when the power switch SW is opened during play mode, the voltage of the power line _L1 will drop rapidly,
Since the base potential of the transistor Tr ₁ becomes lower than the cutoff voltage, the voltage detection circuit 3 connects the drive transistor Tr ₂
The base of the mutating control circuit 1 and the output terminal 2 of the mutating control circuit 1 are opened. Therefore, the drive transistor Tr ₂ has a resistor R ₃ due to the charge stored in the capacitor C.
The mutating transistor Tr ₃ is driven by being in the active state for a time constant period determined by .

Furthermore, when the power switch SW is opened in the stop mode, the driving transistor Tr ₂ becomes active and drives the muting transistor Tr ₃ as described above, so the muting control circuit 1 becomes unstable due to the power cutoff. ,
The muting operation is performed no matter what state the output terminal 2 is in.

Therefore, by opening the power switch SW, the muting operation can be performed reliably in various modes.

Furthermore, when the voltage V ₀ of the power supply E drops below the minimum guaranteed voltage of the amplifier etc. due to various factors, the voltage detection circuit 3 similarly opens the base of the drive transistor Tr ₂ and the output terminal 2 of the muting control circuit 1. , activates the drive transistor Tr ₂ .

Furthermore, the present invention is not limited to the above-mentioned embodiments, and for example, a muting transistor driven by a muting control means and a muting transistor driven by a voltage detection circuit may be provided in parallel on the signal line. It is also possible to use other configurations of the voltage detection circuit, etc.
It can take various forms.

<<Effects of the invention>> As described above, according to the present invention, the muting operation can be performed reliably because the current is supplied from the power line without going through a power switch, rather than from the discharging current of the capacitor, as in the conventional technology of the muting transistor. At the same time, when the power switch is opened, the drive transistor becomes inactive after the muting operation, which is performed for a predetermined period of time, is completed, making it possible to realize an excellent muting circuit that does not use unnecessary current consumption, and is particularly suitable for automotive audio equipment. When applied to the system, it is possible to effectively block noise caused by fluctuations in battery voltage caused by various factors. Also, in the present invention, a capacitor is used as in the prior art, but since this capacitor constitutes a time constant circuit for regulating the driving time of the drive transistor, its capacitance is small. Therefore, it is possible to realize a cost-effective muting circuit.

[Brief explanation of drawings]

The figure is a circuit diagram for explaining one embodiment of the muting circuit according to the present invention. 1... Muting control circuit, 3... Voltage detection circuit, 4... Time constant circuit, _L1 , _L2 ... Power line, Ls... Signal line, _R1 to _R3 ... Resistance,
_D1 , _D2 ...diode, _Tr2 ...driving transistor, _Tr3 ...mutating transistor.

Claims (1)

[Scope of Claim for Utility Model Registration] In a muting circuit that short-circuits a signal line and the ground in a desired mode, a first power line that supplies current to the desired circuit via a power switch, and a first power line that supplies current to the desired circuit without going through the power switch; a second power supply line that supplies current to the circuit; a muting transistor that shorts the signal line and the ground; and a muting transistor that drives the mutating transistor.
a drive transistor to which a collector current is supplied from the second power supply line; and a drive transistor connected to the first power supply line to be charged and to control the active time of the drive transistor when discharging the drive transistor. a capacitor connected to the base of the drive transistor, and a voltage detection circuit that is connected to the base of the drive transistor and controls the drive transistor by detecting that the voltage of the first power supply line has fallen below a predetermined level. A mutating circuit characterized by: