JPS6122345Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a mute drive circuit, and more particularly to a mute drive circuit that performs muting control by driving a mute switch element of a muting circuit in an audio device.

2. Description of the Related Art In audio equipment, so-called muting circuits are widely used to prevent unpleasant sounds generated under various operating conditions and to protect speakers and the like from noises that produce such unpleasant sounds.
The muting operation period of the mutating circuit has an appropriate value depending on the purpose of its operation, and is not uniform. For example, the muting operation period to prevent pop noises when the power is turned on must be selected to be relatively long due to the rise time of the circuit power supply, and on the other hand, to prevent shock noises when switching functions, the muting operation period must be selected to be relatively long. It is sufficient if the muting operation is performed for a short period of time. In order to meet these various demands. It is not economically advantageous to provide different types of muting circuits in the same device, so the muting operation time is selected to be the maximum, and one muting circuit is used for all muting operations. As a result, the mute motion becomes unnatural and undesirable to the auditory sense.

An object of the present invention is to provide a mute drive circuit that has an extremely simple configuration and is capable of mute operations that meet various purposes.

The Mute Drive circuit of the present invention is provided with a time constant circuit that applies a voltage change with a predetermined time constant to the Mute Drive output terminal in response to power-on, and controls the charge in the capacitor of the time constant circuit by a predetermined muting control. A control device is provided with a discharging switch element that instantly discharges in response to a signal, and conduction is controlled in response to another muting control signal to change the voltage of the muting drive output terminal without discharging the charge in the capacitor. A switching element is provided.

The present invention will be explained below based on the drawings.

FIG. 1 is a circuit diagram showing one embodiment of the present invention, in which 1 is a mute drive circuit, and the output from the drive output terminal 2 causes a mute switch 3 to be activated.
This is the intermittent signal that is controlled on and off. In this example, the switch 3 is composed of an N-channel type JFET (junction field effect transistor), and both the source and drain terminals are pulled up to the circuit power supply +Vcc by resistors _R1 and _R2 . .

A resistive element _R3 , which together with a capacitor _C1 constitutes a time constant circuit, is provided between the Miut Drive output terminal 2 and the circuit power supply, and a capacitor _C1 is provided between the capacitor _C1 and the output terminal 2. A unidirectional diode D ₁ is provided that passes only the charging current to. A bipolar transistor _Q1 , to which a first muting signal is applied to the base, is provided between both ends of the capacitor _C1 , and serves as a switching element for discharging the capacitor. This base terminal becomes the first muting control signal application terminal 4. Further, a bipolar transistor _Q2 having a base applied with a second muting signal is provided between the output terminal 2 and the ground, and serves as a switching element for controlling the voltage of the output terminal 2. This base terminal becomes the second muting control signal application terminal 5.

FIG. 2 is a waveform diagram illustrating the operation of the circuit shown in FIG. 1, and A in the figure shows the operation when the power is turned on. When the power is turned on at time T ₀ , the voltage at one end of the resistor R ₃ of the time constant circuit rises at approximately the time of compression as shown by the solid line, and the capacitor C ₁ of the time constant circuit is charged by this voltage. Therefore, the voltage at the Mute Drive output terminal gradually rises with a time constant C ₁ ·R ₃ as shown by the dashed line. Here, if the pinch-off voltage of the mute switch 3 is Vp, the transistor 3 is off until the gate-source voltage of the transistor 3 reaches this pinch-off voltage Vp (t ₀ to t ₁ ); A mute operation is performed when the power is turned on.

Next, the muting control signal that requires a short muting operation is applied for a period of time as shown by the solid line in Figure B.
When the voltage is applied to the input terminal 5 between t ₂ and _{t 3} , the control transistor Q ₂ becomes conductive during that period, and the voltage at the output terminal 2 becomes the ground level as shown by the dashed line B for a short period of time ( t ₂ to _t3 ) is possible. Since this is blocked by the discharging diode D ₁ of the capacitor C ₁ , the voltage at the output terminal 2 instantaneously follows the control input.

Next, when a mutating control signal that requires a large muting period is applied to the input terminal 4 for a period t ₄ to t ₅ as shown by the solid line in Figure C, the charge on the capacitor C ₁ is transferred to the transistor Q in the on state. ₁ , the output terminal 2 transitions to the ground level at time _t4 and controls the mute switch 3 to turn off. After the mutating control signal disappears at time _t5 , the capacitor _C1 starts to be charged, so the voltage at the output terminal 2 changes with a time constant.
It gradually rises with C ₁ and R ₃ . Then, at time _t6 , the gate-source voltage of transistor 3 is
When Vp is reached, transistor 3 becomes conductive. Therefore, the mute operation is performed during the period t ₄ to _{t 6} .

In order to make the muting operation period when the power is turned on longer than the muting operation period caused by the muting control signal applied to the input terminal 4, as shown in FIG. Connect diode D ₂ and capacitor C ₂ to set the time constant of the time constant circuit at power-on as R ₃
This can be achieved by setting it to a larger value (C ₁ +C ₂ ).

FIG. 4 is a circuit diagram showing another embodiment of the present invention, in which parts equivalent to those in FIG. 1 are designated by the same reference numerals. In this example, a terminal 6 to which a third muting control signal is applied is further provided, and the charge of a separately provided capacitor _C3 is discharged by a transistor _Q3 which is made conductive by this control signal. be. Note that a diode _D3 is connected between the output terminal 2 and the capacitor _C3 to prevent the capacitor _C3 from being discharged by the other switching transistors _Q1 and _Q2 .
By appropriately selecting the time constants C ₃ and R ₃ , it is possible to perform operations with different mute periods.

Furthermore, if operations with different muting periods are required, various muting operations can be achieved by adding capacitors, unidirectional diodes, and discharge switching transistors accordingly.
Also in this example, if it is necessary to maximize the mute period when the power is turned on, a capacitor that does not have a discharge transistor at both ends is connected to the output terminal 2 via a unidirectional diode, as shown in Figure 3. Just do it.

In the above, a JFET is used as the miute switch 3, but other switching elements may be used.Furthermore, bipolar transistors _Q1 to _Q3 are used as switching elements, but other elements can be used instead. That is clear.

According to the present invention, muting circuits with different muting operation bases can be obtained with a simple circuit configuration, so that mutating for various purposes becomes possible.
Furthermore, it is suitable for use as a drive circuit for relays, lamps, etc. as an application.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of one embodiment of the present invention, Figure 2A~
C is a timing waveform diagram explaining the circuit operation of FIG. 1, and FIGS. 3 and 4 are circuit diagrams showing other embodiments of the present invention. Explanation of symbols of main parts, 1... Mute drive circuit, 2... Mute drive output terminal, Q ₁
~ _Q3 ...Switching transistor, _C1 ~ _C3 ...
... Time constant circuit capacitor, R ₃ ... Time constant circuit resistor, D ₁ to _{D 3} ... Unidirectional diode.

Claims (1)

[Scope of utility model registration request] a resistive element provided between the circuit power supply and the Miut Drive output terminal, and at least one capacitor that constitutes a time constant circuit together with the resistive element;
A unidirectional element is provided between the output terminal and the capacitor to pass only the charging current to the capacitor, and a discharging switch element is made conductive in response to a predetermined muting control signal to discharge the charge in the capacitor. and a control switch element that becomes conductive in response to another muting control signal and controls the voltage of the mute drive output terminal.