JPS607554Y2 - Muting drive circuit - Google Patents

Description

[Detailed description of the invention] The present invention relates to a muting drive circuit that uses as an input signal the DC voltage that falls when the power to the signal amplifier circuit is turned off. By preventing the muting circuit from operating in response to fluctuations, a stable and reliable muting operation can be performed when the power is turned off.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram of the first embodiment, and 1 and 2 are input terminals.

These input terminals 1 and 2 are connected to the plus and minus power supply lines of the signal amplification circuit, respectively.

That is, the input terminals 1 and 2 accept the power supply voltage as an input signal in order to detect the fall of the power supply voltage, so-called power supply voltage change, when the signal amplifier circuit is powered off.

On the other hand, these input terminals 1 and 2 are power supply input terminals of this circuit, that is, when the power of the signal amplification circuit is turned off, in order to use the power supply energy of this circuit itself that generates a muting output, a capacitor C (described later) is used. It is for charging.

A series circuit of a diode D1 and a capacitor C is connected between the input terminals 1 and 2, and a resistor R□, a diode D2 . A series circuit of D3 resistors R2 is connected, and the emitter and base of the transistor Tr are connected in parallel with the resistor R2.

Reference numeral 3.4 denotes an output terminal for driving the muting circuit, and the output terminal 3 is connected to the collector of the transistor Tr, and the output terminal 4 is connected to the input terminal 2.

With the above configuration, while a DC voltage is constantly applied between input terminals 1 and 2, the base and emitter of the transistor Tr are at the same potential, so the transistor Tr is non-conducting and the output is There is no output between terminals 3 and 4, so this muting circuit is in an inactive state.

Next, when the DC voltage (power supply voltage) applied between input terminals 1 and 2 is turned off, the voltage between input terminals 1 and 2 becomes lower than the voltage stored in capacitor C. The current flows from the emitter to the base circuit of the transistor Tr, making the transistor Tr conductive.

Therefore, the electric charge of the capacitor C becomes a power source through the output terminal 3.4 to operate the muting circuit, and the output of the signal amplification circuit is muted.

Here, for the conduction of the transistor Tr, in the case of a silicon transistor, the voltage between the emitter and the base must exceed 0.6V, which is the voltage when the voltage between the input terminals 1 and 2 drops due to noise etc. Due to the difference in charging voltage of capacitor C, diode D2. The voltage at which current flows through D3 is the voltage across the resistors R1, R2 and the diode D2. The voltage at which the transistor Tr conducts is determined by the resistor R1°R2 and the diodes D2t and D3.

Therefore, the threshold at which the transistor Tr becomes conductive with respect to the voltage drop appearing between the input terminals 1 and 2 is the diode D2.
D3 is determined, and for small DC voltage fluctuations below the threshold value, no output appears at the output terminals 3 and 4, and the present muting circuit does not operate.

Therefore, even when the power source is a battery and the voltage is reduced, the threshold value remains constant.
Muting is not performed for sudden power supply voltage fluctuations within this dark value, making it possible to prevent unnecessary muting.

Note that it is possible to simply provide a threshold value for the conduction of the transistor Tr using only the resistor B and R2, but this causes a loss in driving the base of the transistor Tr.

However, by inserting diodes D2 and D3 and determining circuit constants, voltage fluctuations at terminal 1 can be efficiently transmitted to the base, and the conduction speed becomes faster.

Figure 2 shows the diode D2. D3 is Zener diode D
4, and this configuration also performs exactly the same operation as the one shown in FIG.

As described above, the present invention has two
a series circuit of a diode and a capacitor connected between terminals, a series circuit of a first resistor, a constant voltage element, and a second resistor connected in parallel with the diode, and an emitter connected in parallel with the second resistor. A muting drive circuit characterized by comprising a transistor to which a base is connected and a muting control output is taken out from a collector,
The voltage of the power supply during operation is always held in the capacitor, and if the fluctuation of the power supply voltage with respect to the voltage of this capacitor is within the threshold for switching the transistor, muting operation will not be performed. Even if the state differs from the specified value, muting is not activated due to external noise, ripples, or other fluctuations in the power supply voltage, and stable operation is performed, making it highly practical.

[Brief explanation of the drawing]

1 and 2 are circuit diagrams showing respective embodiments of the present invention. 1.2...Input terminal, 3,4...Output terminal, R1, R2...Resistor, D2. D3...
...Diode, Tr...Transistor.

Claims (1)

[Scope of utility model registration request] a series circuit of a diode and a capacitor connected between two terminals serving as a power input and a signal input; a series circuit of a first resistor, a constant voltage element, and a second resistor connected in parallel with the diode; A muting drive circuit comprising: a transistor whose emitter and base are connected in parallel to a second resistor and whose collector outputs a muting control output.