JPS6336161B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a structure for preventing switch-on shock noise that occurs when power is turned on in a power amplifier circuit used in an acoustic amplifier or the like.

The switch-on sound that occurs when the power is turned on in an audio amplifier is a harsh sound.
Furthermore, in some cases, an excessive current may flow to the speaker and destroy the speaker.

Therefore, the main object of the present invention is to prevent the unpleasant switch-on-shock sound that occurs when the power is turned on, and at the same time to protect the speaker by preventing excessive current from flowing through the speaker.

According to the present invention, the output amplified by the differential amplifier circuit is power amplified, and the output is negatively fed back to the differential amplifier circuit, and the current source transistor and the feedback transistor of the differential amplifier are further connected to each other. and obtain a power amplification circuit that is controlled in response to power up.

Next, the present invention will be explained in more detail with reference to the drawings.

FIG. 1 shows an embodiment of the acoustic amplifier according to the present invention, in which the input stage differential transistors Q ₁ and Q ₃ are PNP transistors, and this circuit will be described below.

Figure 1 shows that when transistors Q ₁ and Q ₃ are PNP transistors, transistor Q ₄ , resistor R ₁₀ , transistor Q ₂ (DC bias voltage of resistor R ₈ and power supply Vcc
), resistor R ₆ , transistor
Q ₅ , resistor R ₁₈ , capacitor C ₂ (also serves as power supply Vcc ripple), capacitor C ₁ (also serves as input coupling)
and resistors R ₁ , R ₂ , R ₃ , and R ₄ (also used for input DC bias) constitute a switch-on shock noise prevention circuit 400.

In response to power-on, Zener diode _D5 generates a predetermined voltage, which is divided by resistors _R15 to _R17 and supplied to the base of transistor _Q4 . Capacitor C ₂ for power supply ripple filter
is not charging at this point. Therefore,
Transistor _Q4 conducts. Since the resistance value of resistor R ₁₀ is chosen small enough, capacitor C ₂ is quickly charged, so that the bias consisting of resistors R ₁ - R ₃ and diodes D ₁ - ^{D 4} is A predetermined bias voltage is generated. resistance
The bias voltage available at the junction of R ₁ and R ₂ causes transistor Q ₂ to conduct, raising the potential at the common emitter of differential PNP transistors Q ₁ and Q ₂ .
As mentioned above, since capacitor C ₂ is rapidly charged in response to power-on, it is no exaggeration to say that transistor Q ₂ immediately becomes conductive in response to power-on. A bias voltage is obtained at the junction of resistors R ₂ and R ₃ , but the input coupling capacitor
Since C ₁ is not charged, the base potential of transistor Q ₁ is approximately 0V.

On the other hand, the bias voltage obtained at the connection point of resistors R ₃ and R ₄ makes transistor Q ₅ conductive, so
The base potential of transistor _Q3 is pulled up.
Therefore, transistor Q ₁ is conductive and Q ₃ remains cut off. As a result, the transistors Q ₇ and Q ₈ of the predriver circuit and the lower transistors Q ₁₁ and Q ₁₄ of the output stage become conductive, and the output terminal V ₀ takes the ground potential. After this, input coupling capacitor
C ₁ is charged through resistor R ₅ and feedback capacitor
C ₃ is charged in transistor Q ₅ via resistor R ₁₂ . When the base potential of transistor Q ₁ approaches the base potential of transistor Q ₃ regulated by the emitter potential of transistor Q ₅ , these transistors Q ₁ and Q ₃ start linear operation, and the output potential V ₀ becomes 1/2 Vcc. begins to rise towards. When the charging voltage of capacitor C ₃ causes the emitter potential of transistor Q ₅ to exceed a potential lowered by the threshold voltage from the base bias potential of the transistor, transistor Q ₅ becomes cut-off, and capacitor C ₃ is then turned off. Charged from the output side. Then, the base potentials of transistors Q ₁ and Q ₃ and the output voltage V ₀ reach predetermined values and become stable.

In this way, large transient currents do not flow through the speaker SP connected to the output, and switch-on shock noise is prevented.

Note that as the capacitor C ₂ is further charged, the transistor Q ₄ is in a cut-off state during normal operation, and a specified bias voltage is generated at each connection point between the resistors R ₁ and _{R 4} .

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment according to the present invention. Q ₁ ……Q ₁₅ ……Transistor, R ₁ ……R ₂₄ ……
Resistance, C ₁ ... C ₉ ... Capacitor, D ₁ ... D ₁₃ ,
D ₁₃ ′...Diode.

Claims (1)

[Claims] 1. First and second transistors of one conductivity type constituting a differential amplifier, means for supplying an input signal to the base of the first transistor via a coupling capacitor, a feedback capacitor whose one end is grounded, and this capacitor. a series circuit of first and second feedback resistors connected between the other end and the output, and a connection point of the first and second feedback resistors is coupled to the base of the second transistor. a feedback circuit for supplying a feedback signal to the base of the second transistor; a feedback circuit having first to third bias output terminals; and a feedback circuit for supplying a feedback signal to the base of the second transistor; a bias circuit that generates a small third bias voltage;
a third transistor of opposite conductivity type that serves as a current source for the differential amplifier and whose collector and emitter are respectively coupled to a power supply terminal and a common emitter of the first and second transistors; a base of the third transistor; means for connecting to the first bias output terminal of the bias circuit; a power supply ripple filter capacitor connected between the first bias output terminal of the bias circuit and a ground terminal; means for connecting the bias output terminal of the second transistor to the base of the first transistor;
a fourth transistor of the opposite conductivity type, the collector of which is coupled to the bias output terminal of the transistor, respectively, to the power supply terminal; a fourth transistor connected between the power supply terminal and the ground terminal and having a voltage lower than the first bias voltage;
means for supplying a bias voltage to the base of the fourth transistor;
A power amplifier circuit comprising: a fifth transistor of the opposite conductivity type, the base of which is coupled to the third bias output terminal of the bias circuit, and the collector of which is coupled to the power supply terminal.