JPS5915124Y2 - power amplifier circuit - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a power amplifier, and particularly to a 5EPP circuit used in a stereo power amplifier or the like.

In a stereo power amplifier, when a signal from a voltage amplifier in the previous stage is received to drive a speaker, the output signal of the power amplifier clips in the output waveform when it exceeds a predetermined level determined by the power supply voltage.

Furthermore, at the same time, the output transistor becomes saturated between its collector and emitter, and this saturation causes abnormal operations such as parasitic oscillation, resulting in the problem that stable feedback cannot be achieved.

As a means to solve the above-mentioned problem, a circuit shown in FIG. 1 has conventionally been used.

That is, in FIG. 1, transistors Q2,3 and Q4,5
It is a pure complementary 5EPP circuit composed of
EE2 is supplied.

Further, the transistor Q1 is a voltage amplification transistor,
The output signal is transferred to the transistor Q2. In addition to the base of Q4, it is amplified by the 5EPP circuit and drives a speaker connected to the output terminal.

In addition, a resistor R is connected between the base and collector of the transistor Q2.
t, a diode D1 is connected in series, the cathode of the diode D1 is connected to the collector of the transistor Q2, and the anode is connected to the connection point a with the resistor R1.

Also, a resistor R2 is connected between the base and collector of the transistor Q4.
, and a diode D2 are connected in series, and the anode of the diode D2 is connected to the collector of the transistor Q4, and the cathode is connected to the connection point with the resistor R2. A power supply voltage VCC1 supplied to is connected to the connection point Sukara, and a collector output terminal of a voltage amplification transistor Q1 is connected to the connection point Sukara.

In the above configuration, the power supply voltage vCC1 is equal to VCC
2 and VEE2, if the signal applied to the base of voltage amplifying transistor Q1 is negative, transistor Q2 . It is amplified by Q3, and as the signal level increases, the potential at point a also increases accordingly.

If the potential at point a is below the power supply voltage ■C02, diode D
1 is off, transistor Q2 . Q3 is operating in the operating region.

If the signal becomes excessive and the potential at point a becomes larger than the power supply voltage vCC2, diode D1 becomes conductive, and the potential at point a becomes VCC.
2 and the voltage drop across resistor R1 is VR□, the base potential of transistor Q2 is (VCC2-VR
□) The base-collector potential becomes VRI, and the transistor Q2. Saturation of Q3 can be prevented.

If the signal is positive, transistor Q4. The potential at point b, which is amplified by Q5, is clamped by diode D2, and transistors Q, , Q operate in the same manner as the positive side signal described above.
5 saturation can be prevented.

However, in the circuit of FIG.
2. The base-collector voltage of Q4 and the potential at points a and l) are determined by the voltage drop across resistors R1 and R2, and this voltage drop varies depending on the signal level, so transistor Q
2. Even if the collector-base capacitance of Q4 changes and the saturation phenomenon can be suppressed, the amount of feedback fluctuates due to the capacitance change, making it impossible to always obtain stable output characteristics.

This proposal has been made in view of this point, and an embodiment will be described below with reference to FIG. 2 (the same parts as in FIG. 1 are denoted by the same reference numerals).

In FIG. 2, an appropriate number of diodes D3, . D4 (four each in the embodiment) are connected to constitute a constant voltage source.

When a negative signal is input to the base of the transistor Q1, the signal level becomes excessive and the potential at point a becomes higher than the power supply voltage VCC2. 'Dt becomes conductive, and the potential at point a is clamped and never becomes higher than the power supply voltage VCC2.

Also, if the voltage across the diode D3 is D3, the base potential of the transistor Q2 is (VCC2-D3), and the base-collector voltage is VD3, which remains constant even when the signal level changes. If VD3 is set to an appropriate value by diode D3, l-transistor Q2
Since the base-collector voltage of is constant, the base-collector capacitance does not change even when the signal level changes.
Stable return is always applied.

In addition, in the case of a positive signal, the power supply voltage V is
It is clamped to EE2, and the same effect as described above can be obtained by the constant voltage diode D4.

As described above, according to the present invention, it is possible not only to prevent parasitic oscillation due to saturation of the output transistor when an excessive signal is present, but also to prevent changes in the signal level due to the constant voltage circuit inserted between the base and collector of the output transistor. It is possible to always obtain stable output characteristics, and the amount of feedback applied to the signal system can be kept constant.

In the embodiment, a diode was used as the constant voltage circuit, but the same effect can be obtained by using a variable impedance element such as a transistor or a varistor.

Furthermore, the present invention is not limited to 5EPP circuits, but can also be applied to amplifier circuits such as push-pull amplifier circuits and single amplifier circuits.

[Brief explanation of drawings]

FIG. 1 shows a conventional power amplifier circuit, and FIG. 2 shows a power amplifier circuit according to an embodiment of the present invention. Q1~5...transistor, DI~4...
...Diode, 1...Bias circuit, R1,
2...Resistance.

Claims (1)

[Scope of utility model registration request] a first power supply voltage supplied to the collector of the power amplification transistor; and a second power supply voltage larger than the first power supply voltage supplied to the voltage amplification transistor, the first power supply voltage of the power amplification transistor; A base, which is a signal input terminal to which an output signal of the voltage amplification transistor is applied from a side terminal, is normally off, and the level of the output signal input to the base of the power amplification transistor is determined by the first power supply voltage. A power amplifier circuit characterized in that a constant voltage circuit is inserted through a diode connected to turn on when a predetermined level is exceeded.