JPS6325764Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a muting circuit, and more particularly to a power muting circuit that prevents excessive noise from occurring at the output of a power amplifier when the power is turned on or off.

In recent years, with the rapid development of electronic technology, there has been a trend toward smaller power amplifiers with larger outputs. In this case, the power amplifier is driven by a regulated power supply B ₁ used in its input stage and an unregulated power supply B ₂ used in its output stage, and the voltage is generally such that B ₁ > B ₂ . In a relationship. and,
Regarding the power supplies that supply voltage to this power amplifier, the stabilized power supply B ₁ rises and falls slowly, and the unregulated power supply B ₂ rises and falls quickly. As a result, click noise occurs in the amplifier output due to the voltage difference caused by the difference in rise and fall characteristics of the two power supplies when the power switch is turned on and off.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a power supply muting circuit that prevents the clicking noise that occurs at the output of a power amplifier when the power is turned on and off.

In order to achieve these objectives, the present invention utilizes the voltage difference caused by the difference in rise and fall characteristics between the regulated power supply _B1 and the unregulated power supply _B2 to control the output stage transistor of the power amplifier. This prevents the generation of excessive noise that occurs when the power is turned on and off. Hereinafter, it will be explained in detail using the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the power supply muting circuit according to the present invention, in which 1a and 1b are supplied with stabilized power supplies +B ₁ and -B ₁ supplied from a power supply section (not shown). a first power terminal;
2a and 2b are second power supply terminals to which unregulated power supplies +B ₂ and -B ₂ are supplied from a power supply section (not shown), and the characteristics of the regulated power supplies +B ₁ and -B ₁ are shown in Fig. 2. As shown by curve A, the rise and fall characteristics when the power switch is turned on and off are gradual, and the characteristics of unregulated power supplies +B ₂ and -B ₂ are as shown by curve B in Figure 2. The rise and fall characteristics when the power switch is on and off become steep, and the voltage in the steady state is +
The relationship is B ₁ >+B ₂ . 3 is an input terminal to which the signal to be amplified is supplied, Q ₁ and Q ₂ constitute a differential amplifier, and the stabilized power supplies +B and -B supplied between the first power supply terminals 1a and 1b are input as power supplies. A transistor that amplifies the signal input to terminal 3, _Q3 is a transistor whose base input is the amplifier output generated across the load resistor R1 of the differential amplifier constituted by the transistors _{Q1 and Q2} . , this transistor _Q3 is connected to the first power supply terminal 1a,
Between 1b, resistor R ₂ , diode group D ₁ , resistors R ₃ , R ₄
connected via. Q ₄ and Q ₅ are output stage transistors connected in Darlington between the second power supply terminal 2a and the output terminal 4, and the output of the transistor Q ₃ is connected from the connection point between the resistor R ₂ and the diode group D ₁ . The extracted signal is amplified.
Q ₆ and Q ₇ are transistors connected in Darlington between the second power supply terminal 2b and the output terminal 4.
This transistor has the opposite polarity to Q ₄ and Q ₅ , and amplifies the collector output of transistor Q ₃ . That is, transistors Q ₄ , Q ₅ and transistors
Q ₆ and Q ₇ constitute the final stage push-pull amplifier. The emitter of Q ₈ is connected to the second power supply terminal 2a via the forward-connected diode D ₂ , and the stabilized power supply +B ₁ supplied to the first power supply terminal 1a is input as the base via the resistor R ₅ . Transistor C is a relatively large capacitor that charges the output of diode D ₂ , Q ₉ and Q ₁₀ use the on output of transistor Q ₈ as base input via resistors R ₆ and R ₇ , and transistors Q ₄ and Q This is a muting transistor that bypasses the signals input to each base of ₆ .

In the circuit configured as described above, when the power switch of the power supply circuit (not shown) is turned on, the regulated power supplies +B ₁ , -B ₁ and the unregulated power supplies +B ₂ , -B ₂ are curved as curves A and B in Fig. 2. Rise as shown. Further, the potential across the capacitor C connected to the cathode side of the diode _D2 also rises approximately along the potential of the unregulated power supply + _B2 , as shown by the dotted line C in FIG.

In this case, transistor Q ₈ is connected to the regulated power supply +B ₁
It is turned on only during the period until the voltage of the capacitor C becomes equal to or higher than the potential across the capacitor C, that is, during the time T1 in _FIG . As a result, transistors Q ₉ and Q ₁₀ whose base input is the output of transistor Q ₈ are also turned on. When transistors Q ₉ and Q ₁₀ are turned on, the transistors that make up the push-pull amplifier
The bases of Q ₄ and Q ₆ are respectively dropped to the midpoint potential. Therefore, the period T ₁ shown in FIG.
In this case, the inputs of transistors Q ₄ and Q ₆ are forcibly bypassed to prevent excessive noise that occurs when the power is turned on.

Next, when the power switch is turned off, the regulated power supply
B ₁ descends relatively slowly as shown in Figure 2. On the other hand, the potential +B ₃ across the capacitor C is prevented from flowing backward by the diode D ₂ , so it drops extremely slowly as shown by the dotted line C in FIG. Therefore, the transistor _Q8 is turned on during a period when the potential of the stabilized power supply + _B1 serving as the base potential is lower than the potential across the capacitor C, that is, during the period _T3 shown in FIG. When transistor Q ₈ turns on, transistors Q ₉ and Q ₁₀ also turn on, and transistors Q ₄ and Q ₆
Bypass all signals input to the base of the Therefore, even when the power switch is turned off, generation of excessive noise that is output when the power is turned off is prevented. Therefore, in the circuit configured as described above, since the output stage is forcibly rendered inactive when the power is turned on and off, generation of excessive noise when the power is turned on and off is reliably prevented.

In addition, in the above embodiment, only the case where it is applied to a push-pull amplifier circuit was explained.
The present invention is not limited to this. Also,
The muting control transistor _Q8 is not limited to the positive power supply side, and a transistor with the opposite polarity may be provided on the negative power supply side.

As explained above, the power supply muting circuit according to the present invention skillfully utilizes the characteristics of a regulated power supply and an unregulated power supply, and therefore, although it has a simple circuit configuration, it is able to withstand excessive It has an excellent effect of reliably preventing the generation of sound.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a power supply muting circuit according to the present invention, and FIG. 2 is a waveform diagram of each part for explaining the operation of FIG. 1. _Q1 to _Q10 ...transistor, _R1 to _R7 ...resistance,
D ₁ , D ₂ ... Diode, +B ₁ , -B ₁ ... Stabilized power supply, +B ₂ , -B ₂ ... Unregulated power supply.

Claims (1)

[Scope of utility model registration request] A first amplifier circuit that uses a stabilized power supply with gradual rise and fall characteristics, and a second amplifier circuit that uses an unregulated power supply that has a lower potential than the stabilized power supply and has steep rise and fall characteristics. In a power supply mutating circuit of a power amplifier connected to a circuit, a capacitor whose other end is grounded charges the unregulated power supply output via a forward diode, and one end of the capacitor is used as an emitter input, and the stabilized power supply output and a second transistor that is controlled by the collector output of the first transistor and bypasses the signal input to the output stage transistor of the second amplifier to the output terminal. Power muting circuit.