JPH0458201B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power amplifier, and more particularly to a power amplifier equipped with a shock noise prevention circuit for preventing the shock noise generated when the power amplifier is turned on.

Various prevention circuits of this type have been proposed in the past, some of which utilize ripple filter circuits that remove ripples from the power supply voltage.

That is, the ripple filter circuit has a capacitor to remove ripple components, and the voltage of this capacitor is zero when the power is turned on and gradually increases thereafter. Therefore, the voltage at the output terminal is gradually raised by utilizing changes in the voltage of the capacitor. However, when the power is turned on, there is no function as a ripple filter, and therefore, in the above-described shock noise prevention circuit, a hum component superimposed on the power supply appears at the output terminal.

Hereinafter, conventional problems and the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the present invention. Circuit A surrounded by dotted lines is the main part of the present invention, and if circuit A is not present, a conventional ripple filter circuit can be used to prevent shock noise. It can be thought of as indicating the power amplifier used in the circuit.

First, the operation without circuit A will be described. In the circuit shown in Figure 1, a is an input terminal, b is a negative feedback terminal, and terminal g is a power supply terminal. When a steady bias voltage is applied to terminal g, terminal a
The input signal applied to is amplified by transistors Q ₃ and Q ₄ that constitute a differential amplifier, inverted in position by transistors Q ₅ and Q ₆ that constitute a position inversion amplifier, and further inverted by a preamplifier. The signal is amplified by the constituting transistor _Q13 and is amplified by the single-ended push-pull output circuit, and the signal output is taken out from the speaker S. The single-ended push-pull output circuit consists of transistors Q ₁₄ , Q ₁₉ , Q ₂₀ and Q ₂₁ , and transistors Q ₁₂ , Q ₁₅ , Q ₁₇ and Q ₁₈ are for passing idling current to the output circuit. be. This idling current is supplied for the purpose of eliminating switching distortion by always passing a constant current between transistors _Q19 and _Q20 that constitute the output circuit.

The relationship between the base-emitter voltage of transistors Q ₁₉ and Q ₂₀ and the base-emitter voltage of transistors Q ₁₂ , Q ₁₄ , Q ₁₇ , and Q ₁₈ is V _BEQ19 +V _BEQ20 = V _BEQ12 −V _BEQ14 +V _BEQ17 +V _BEQ18 Therefore, by setting the current values flowing through these Q ₁₂ , Q ₁₄ , Q ₁₇ , and Q ₁₈ to predetermined values, the current value of the idling current can be determined. The output signal is fed back from terminal e to the base of the transistor _Q4 of the differential amplifier mentioned above by a negative feedback circuit composed of resistors _R1 , _R8 and capacitor _C1 to improve DC bias and amplification distortion factor. can be measured. The capacitor _C4 is a bootstrap capacitor connected to sufficiently drive the output transistors _Q19 and _Q20 , which amplify the positive half cycle of the large signal output, into the saturation region, thereby increasing the output power. In addition, the transistor Q ₇ , the resistor R ₁₀ , and the capacitor C ₂ constitute a ripple filter circuit, and in a steady state, the ripple component is
It will be removed by a filter of R ₁₀ and capacitor C ₂ . Transistors Q ₁₀ , Q ₁₁ , and Q ₁₆ constitute a constant current source using a current mirror circuit.
In particular, the transistor Q ₁₀ is driven by the transistor Q ₉ , and the transistors Q ₁₁ and Q ₁₆ flow current to the driver transistor Q ₁₃ and the idling current setting section, respectively. The base of transistor Q ₈ is connected to the base of transistor Q ₇ via two diodes D ₅ and D ₆ . The collector of transistor _Q8 is connected to the ground terminal d, and the emitter is connected to the transistor
Each is connected to the Q ₁₁ collector.

In such a configuration, the influence of the power supply ripple on the transistors Q ₁₉ and Q ₂₀ configuring the output circuit is affected by the negative feedback path to the output terminal e consisting of C ₁ , R ₈ , and R ₉ on the collector. Since the impedance of the base is lowered, the influence becomes smaller, and the influence from the base can be prevented by the constant current circuit.

Transistor Q ₈ and diodes D ₅ and D ₆ together with the aforementioned ripple filter circuit constitute a shock noise prevention circuit when the power is turned on. That is, the power terminal g
Immediately after the power is turned on, the capacitor _C2 connected to the terminal C is not charged, so the potential of this power supply terminal is close to 0V.
Therefore, the potential is not supplied from the power supply terminal via the resistor _R6 to the constant current circuit consisting of the diode _D1 , _D2 transistor _Q9 and the resistor _R11 , so the base potential of the transistor _Q9 does not rise and this Q ₉ becomes non-conductive, and transistors Q ₁₀ , Q ₁₁ , and Q ₁₆ become disconnected. Therefore, the output circuit does not start up.

Capacitor C ₂ connected to terminal C is charged through resistor R ₁₀ and the base potential of transistor Q ₇ rises, and the resistor increases from the emitter of transistor Q ₇ .
When a potential is applied to the base of transistor Q ₉ through R ₆ , the constant current circuit of transistors Q ₁₀ , Q ₁₁ , and Q ₁₆ operates, and the collector current of transistor Q ₁₁ drives transistors Q ₁₉ and Q ₂₀ to produce an output. The terminal rises. However, since the base of transistor Q ₈ is connected to terminal C via diodes D ₅ and D ₆ , its emitter is connected to the base of transistor Q ₁₉ , and its collector is connected to ground terminal d, _the The base potential is
It is controlled by the rise of the emitter potential of transistor _Q8 . Since the base of this transistor _Q8 is connected to the terminal C via the diodes _D5 and _D6 , as a result, the rise of the output terminal e increases in response to the voltage of the terminal c, and the resistor _R10 and the capacitor _C2
It shows a gradual rise determined by the time constant of . The rise of the output terminal e charges the capacitor _C1 through the resistor _R9 of the feedback circuit, and when the potential of the terminal b becomes equal to the base potential of the transistor _Q3 , the voltage of the output terminal gradually decreases to half the power supply voltage. It is pulled back to produce a constant amplification effect. In this way, the output terminal e fluctuates slowly from the time the power is turned on until the steady state is reached, so that no transient sound is generated in the speaker. In steady state, transistor _Q8 is reverse biased by the voltage on capacitor _C2 .

However, in recent years, voltage amplification circuit technology has improved and the ability to eliminate power supply voltage fluctuations in the steady state has improved.
Furthermore, due to the reduction in price and miniaturization of audio equipment, the hum component superimposed on power supplies used in audio equipment tends to increase.Especially in equipment that requires a large current when starting up the power, such as a motor, the hum component increases significantly when the power is turned on. A large hum component will be superimposed on the power supply.

If the circuit in Figure 1 does not have the circuit A surrounded by the dotted line, the rise of the output terminal e will respond to the rise of the power of the terminal C even though there is no ripple filter function when the power is turned on, so the resistor R ₁₀ A hum component determined by the time constant of capacitor _C2 will appear at the output terminal.

In order to reduce the hum component from the terminal C, it is necessary to make the time constants of the resistor _R10 and the capacitor _C2 sufficiently large, which has the disadvantage of slowing down the rise time when the power is turned on. The present invention seeks to provide a circuit that solves this problem.

The power amplifier according to the present invention includes a ripple filter circuit that includes a resistor and a capacitor connected in series between the power supply terminals to remove ripples from the power supply voltage, and a power supply circuit that uses the charging voltage of the capacitor to power the power amplifier. In a power amplifier equipped with a shock noise prevention means for suppressing sudden potential fluctuations at the output terminal when the power is turned on, a power failure current source is provided in parallel with the above resistor, and this constant current source is operated when the power is turned on, and the above capacitor is The present invention is characterized in that the constant current source is kept in a non-operating state in a steady state.

FIG. 1 shows an embodiment of the invention by adding a circuit A surrounded by a dotted line. Circuit A is
Transistor Q ₂₂ , Diodes D ₃ , D ₄ , Resistor R ₇ ,
Consists of R ₁₄ and switch W. power terminal g
- Diodes D ₃ and D ₄ , a switch W, and a resistor R ₇ are connected in series between the ground terminal d, and a series circuit of a resistor R ₁₄ and a base-emitter path of a transistor Q ₂₂ is connected in parallel with the diodes D ₃ and D ₄ . Ru. The collector of transistor Q ₂₂ is connected to capacitor C ₂ . When the power supply voltage is supplied, the transistor
A voltage determined by diodes D ₃ and D ₄ is supplied to the base of Q ₂₂ , and the voltage of diodes D ₃ and D ₄ is a substantially constant voltage that is not dependent on the ripple portion of the power supply voltage. Therefore, transistor Q ₂₂ acts as a constant current source and charges capacitor C ₂ with constant current. Therefore, the ripple component does not substantially appear in the capacitor _C2 , and the ripple component is no longer output to the output terminal e. In steady state, the switch circuit W
This constant current circuit is cut off by the constant current circuit.

FIG. 2 shows an example of a circuit specifically implementing this switch circuit W. In FIG. 2, terminals commonly connected to those in FIG. 1 are given the same symbols. Second
The collector of transistor Q ₂₆ in the circuit shown is connected to the base of transistor Q ₂₂ in the circuit of FIG. The switch circuit W includes transistors Q ₂₄ and Q ₂₅
and a comparator with resistor R ₁₆ , which compares the voltage at terminal C to which capacitor C ₂ is connected with resistors R ₁₅ , R ₁₇
Compare the voltage obtained with the diodes D ₇ , D ₈
to control transistor _Q26 .

Next, the operation of the circuit shown in FIG. 2 when the power is turned on will be explained. When power is applied to power terminal g,
The base of the transistor Q ₂₄ is given a divided voltage of the voltage at the terminal f by the resistors R ₁₅ and R ₁₇ , and the base of the transistor Q ₂₅ is connected to the terminal C, so as shown in Fig. 1. However, as capacitor C ₂ charges, the base voltage of Q ₂₅ rises. Therefore, transistor Q ₂₅ conducts, causing transistor Q ₂₆ to conduct, thereby causing transistor
Q ₂₂ conducts and supplies constant current to capacitor C ₂ . If this constant current value is selected appropriately, even if the value of resistor _R10 is set sufficiently large to improve the hum rejection ratio, the constant current supplied by transistor _Q22 will cause the rise of capacitor _C2. You can hasten it. Therefore, the rise of the power amplifier can be appropriately set. The potential of terminal C increases and the resistance
When the potential becomes equal to or higher than the divided potential of _R15 and _R17 , transistor _Q24 becomes conductive and transistor _Q25 turns off.
Transistors Q ₂₆ and Q ₂₂ are also turned off.

Therefore, in steady state, the base current of transistor _Q7 is supplied through resistor _R10 .

As described above, by using the present invention, it is possible to realize a power amplifier that can extremely reduce the hum noise that appears through the circuit that prevents the shock noise when the power is turned on, and that starts up quickly when the power is turned on.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing one embodiment of the present invention, Figure 2 is a circuit diagram showing an embodiment of the present invention.
The figure is a specific circuit diagram of the switch circuit W in the circuit of FIG. 1. In the figure, R ₁ to R ₁₈ ... resistance, D ₁ to D ₈ ...
…Diode, Q ₁ to Q ₂₆ … Transistor, C ₁
~ C ₄ ... Capacitor, S ... Speaker, a
...Input terminal, b...Feedback terminal, c...Ripple filter terminal, d...GND terminal, e...Output terminal, f...Bootstrap terminal, g...Power supply terminal, W...Switch circuit Each is shown below.

Claims (1)

[Claims] 1. A ripple filter circuit that includes a resistor and a capacitor connected in series between power supply terminals and removes ripples in the power supply voltage, an output circuit connected between the power supply terminals, and the capacitor that increases as the power is turned on. voltage generating means that generates a voltage corresponding to a change in charging voltage during a period from power-on to a steady state, and voltage supply means that supplies the voltage from the voltage generating means to the output circuit, and when the power is turned on, the output circuit A power amplifier that suppresses sudden changes in the input voltage of the circuit and suppresses sudden potential fluctuations at the output terminal of the output circuit includes a constant current source connected in parallel to the resistor, and a constant current source connected in parallel to the resistor. By providing means for operating the capacitor by the constant current source to charge the capacitor when the power is turned on, and disabling the constant current source in the steady state, ripples at the time the power is turned on are removed. A power amplifier featuring: