JPS6119544Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power amplifier circuit that operates with almost the same power efficiency as class B amplifier operation and does not generate switching distortion.

Conventionally, single-ended push-pull (hereinafter abbreviated as SEPP) circuits have been frequently used in power amplifier circuits for audio, and in order to achieve particularly good power efficiency, a predetermined idling current flows. Class B biased to perform class amplification operation
SEPP power amplifier circuit is adopted.

However, in a class B SEPP power amplifier circuit, the transistors that supply current to the load are different depending on the input period of the positive half cycle of the input signal and the input period of the input signal of the negative half cycle; Switching of the transistor is performed in accordance with the change of the period, and there is a drawback that switching distortion occurs due to the carrier accumulation effect of the transistor.

The present invention has been developed in consideration of the above, and eliminates the above drawbacks, operates with almost the same power efficiency as class B amplification, and responds to the switching of the input period of the positive and negative half cycles of the input signal. The object of the present invention is to provide a power amplification circuit that does not cause transistors to switch due to switching, and the present invention will be explained below using examples.

The drawing is a circuit diagram of a power amplifier circuit according to an embodiment of the present invention.

In the power amplifier circuit of this embodiment, transistors 1 and 2 constituting the output stage have their erectors connected to the positive and negative power supply terminals +B and -B, respectively, and their emitters are passed through resistors 5 and 6 separately to one end. is connected to a grounded load 7 to form a SEPP circuit, and an input signal is applied to the input side of transistor 1 through a transistor 3 whose base is grounded, and to the input side of transistor 2 through a transistor 4 whose base is grounded. A bias circuit 8 is connected between the emitters of transistors 3 and 4 to generate a constant bias voltage based on the output current of a voltage amplification stage (not shown).

On the other hand, between the base and emitter of transistors 3 and 4, resistors 9 and 10, which generate a voltage that turns on transistors 3 and 4 by the flowing current, are connected respectively, and the base of transistor 3 and the emitter of transistor 1 are connected separately. A plurality of diodes 11 connected in series are connected between the emitter of the transistor 2 and a plurality of diodes 12 connected in series between the emitter of the transistor 2 and the base of the transistor 4, respectively.
A resistor 13 is connected between the bases of transistors 3 and 4.

In the power amplifier circuit configured as described above, the voltage of the bias circuit 8 is set so that the power amplifier circuit performs approximately class B amplification operation.

Therefore, when there is no input signal, a substantially constant current flows through the resistors 9, 10, and 13 due to the voltage of the bias circuit 8, and the current flowing through the resistors 9 and 10 causes
Transistors 3 and 4 are set to be in an on state, and transistors 1 and 2 are also set to be in an on state by collector currents of transistors 3 and 4. The current of transistors 1 and 2 when there is no input signal is determined by the base-emitter voltage V _BE of transistors 3 and 4 and the voltage across diodes 11 and 12 by the bias circuit 8 applied between the emitters of transistors 3 and 4. It is determined by the voltage subtracted from the voltage.

When a positive half-cycle input signal is applied to this power amplifier circuit, the emitter potentials of transistors 3 and 4 move in the positive direction, and the base current of transistor 1 is input to the base current when there is no input signal. A current with a superimposed signal flows in, and a current that amplifies the input signal flows through the emitter of transistor 1, flows into load 7 through resistor 5, and causes load 7 to generate power that is the amplified input signal. Transistor 4 attempts to move in the off direction. On the other hand, if the emitter current of transistor 1 increases,
Although there is almost no change in the voltage between the base and emitter of transistor 3 and the potential difference between both ends of diode 11, the voltage drop occurring across resistor 5 increases. This increase in voltage drop across resistor 5 turns diode 12 off. But transistor 4
Since transistor 2 is always kept on by the current flowing through the paths of resistors 9, 13, and 10, transistor 2 is not turned off and remains on even during the application period of the positive half-cycle input signal. Ru.

In addition, when a negative half-cycle input signal is applied, the same effect as above occurs, and although detailed explanation will be omitted, transistors 1 and 3, which do not directly contribute to the amplification effect, are also not turned off during this period. remains on.

Therefore, regardless of the polarity of the input signal, or even when the polarity of the input signal is switched, transistors 1, 2, 3, and 4 are always maintained in the on state without turning off, and there is no switching. No switching distortion occurs. In addition, the transistor that contributes to the amplification effect and supplies current to the load changes depending on the polarity of the input signal.
Its power efficiency is approximately the same as for class B amplification operation.

Alternatively, the cathode of the diode 11 may be connected to the base of the transistor 1 instead of the emitter of the transistor 1, as shown by the broken line in the drawing, and the anode of the diode 12 may be connected to the base of the transistor 2. A reverse voltage is directly applied between the bases and collectors of the transistors 3 and 4 by diodes 11 and 12, and the same effect as described above is performed and the same effect can be obtained.

The reason why a plurality of diodes connected in series to diodes 11 and 12 is used is to increase the base-collector voltage of transistor 3 or 4 during amplification.

As explained above, according to the present invention, all transistors always operate in the on state regardless of the polarity of the input signal, and are never switched.
No switching distortion occurs.

Furthermore, the transistors that cause current to flow through the load are switched depending on the polarity of the input signal, and the power efficiency is almost the same as in the case of class B amplification operation.

[Brief explanation of the drawing]

The drawing is a circuit diagram of an embodiment of the present invention. 1, 2, 3 and 4...transistor, 7...
Load, 8...bias circuit.

Claims (1)

[Scope of utility model registration request] The input side of the first and second transistors is connected to a single-ended push-pull amplifier circuit consisting of first and second transistors whose emitters are respectively connected to a load through first and second resistors. A third and fourth transistor with a common base connected to a bias circuit that applies a constant voltage bias between each emitter is connected separately, and a third and fourth transistor with a common base is connected between the base and emitter of the third and fourth transistors. A third and a fourth resistor are respectively connected between the base of the third transistor and the emitter or base of the first transistor, and between the emitter or base of the second transistor and the base of the fourth transistor. 1. A power amplification circuit characterized in that at least one diode is connected between the bases of the third and fifth transistors, and a fifth resistor is connected between the bases of the third and fifth transistors.