JPS6119542Y2 - - Google Patents

Description

Detailed Description of the Invention The present invention relates to a power amplifier circuit which operates with almost the same power efficiency as in the case of class B amplification and which does not generate switching distortion.

Single-ended pushpull (hereinafter abbreviated as SEPP) is used as a power amplifier circuit for audio.
Circuits, especially class B circuits with bias settings to flow a predetermined idling current for good power efficiency.
A SEPP power amplifier circuit is used. B class
In SEPP power amplifier circuits, switching distortion occurs during transistor switching due to the carrier accumulation effect of the transistors. For this reason, conventionally,
As shown in FIG. 1, a diode 5 is connected between the emitter of transistor 1 and the collector of transistor 3.
Transistors 1 and 3 are connected in an inverted Darlington connection, the collector of transistor 3 is connected to load 7 through resistor 6, and diode 8 is connected between the emitter of transistor 2 and the collector of transistor 4. transistors 2 and 4
The collector of the transistor 4 is connected to the load 7 through the resistor 9, and the bias circuit 11 for biasing with a constant voltage is connected between the bases of the transistors 1 and 2.
There is a power amplifier circuit that constitutes a SEPP power amplifier circuit and has a resistor 10 connected between the emitters of transistors 1 and 2.

In the conventional power amplifier circuit shown in FIG. There is no off state, with transistors 1 and 3 powering the load when a positive half-cycle input signal is applied, and transistors 2 and 4 powering the load when a negative half-cycle input signal is applied. The device operates with almost the same power efficiency as class B operation, and since transistors 1, 2, 3, and 4 are not turned on or off, switching distortion due to transistor switching does not occur.

However, on the other hand, diodes 5 and 8 are in the off state separately during the input period of the input signal of the negative half cycle and the input period of the input signal of the positive half cycle, due to the carrier accumulation effect of the diodes 5 and 8. The switching current of the diodes 5 and 8 flowing in the opposite direction of the diodes (for example, when the input signal changes from a negative half-cycle to a positive half-cycle, as shown by arrow A in FIG. 1), the transistor 1, 2 and is amplified by transistors 3 and 4, which has the drawback of causing switching distortion due to the diode.

The present invention has been made in consideration of the above, and has as its object to provide a power amplifier circuit which eliminates the above drawbacks, operates with almost the same efficiency as class B amplification, and does not generate switching distortion due to switching of not only transistors but also diodes. This object can be achieved by the present invention by providing a current path through which a switching current flows when the diode is off, thereby causing rapid switching of the diode.

The present invention will be explained below with reference to examples.

FIG. 2 is a circuit diagram of an embodiment of the present invention. In FIG. 2, the same components as those of the power amplifier circuit shown in FIG. 1 are given the same reference numerals.

The power amplification circuit according to one embodiment of the present invention includes transistors 1, 2, 3, and 4, resistors 6 and 7, diodes 5 and 8, and bias circuit 11.
A power amplifier circuit is constructed by connecting a resistor 12 between the emitter of transistor 1 and the collector of transistor 4 in place of resistor 10, and a resistor 13 between the emitter of transistor 2 and the collector of transistor 3, respectively. do. Note that +B and -B
are the positive and negative power terminals.

In the power amplifier circuit shown in FIG. 2, when there is no input signal, the setting of the bias circuit 11 causes a current to flow through the resistors 12 and 13 so that transistors 1, 2, 3, and 4 are turned on. , 2, 3 and 4 are in the on state, and B
It is set to perform class amplification operation.

When a positive half-cycle input signal is applied, the input signal is amplified by transistors 1 and 3, and the emitter current of transistor 1 and the collector current of transistor 3 flow through resistor 6 to load 7, supplying power. supply Therefore, due to the voltage drop across the resistor 6, the diode 8 is no longer able to maintain its on state and turns off.
There is no change in the voltage across the transistors (0.6V in this embodiment), and the transistors 2 and 4 are maintained in the on state without being turned off.

However, since the diode 8 shifts to the OFF state, that is, switches, a switching current flows in the diode 8 in the opposite direction due to the carrier accumulation effect, as described above. However, the switching current of diode 8 is resistor 9, resistor 6, resistor 1
Since the current flows through the path 3, switching of the diode 8 is performed quickly, and the switching current of the diode 8 does not flow through the transistor 1, so that switching distortion due to switching of the diode 8 does not occur.

Of course, transistors 2 and 4 do not perform switching, and no switching distortion occurs due to transistor switching.

Further, since the operation when a negative half-cycle input signal is applied is the same as that described above, a detailed explanation thereof will be omitted.

As explained above, according to the present invention, the transistors that contribute to the amplification effect and mainly supply power to the load are switched by the positive and negative half-cycle input signals, similar to the case of class B, but all The transistor is always on and no switching is performed, so switching distortion due to transistor switching does not occur. Furthermore, since a current path for the diode switching current is formed during diode switching, the diode switching speed is increased, and the diode switching current does not flow to the transistor, so that switching distortion due to diode switching does not occur. Moreover, the power efficiency is almost the same as in the case of class B amplification operation.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional power amplifier circuit. FIG. 2 is a circuit diagram of a power amplifier circuit according to an embodiment of the present invention. 1, 2, 3 and 4...transistor, 5 and 8...diode, 6...load, 11...bias circuit.

Claims (1)

[Scope of utility model registration request] A first diode is connected between the emitter of the first transistor and the collector of the second transistor to form an inverted Darlington connection between the first transistor and the second transistor. an inverted Darlington transistor connected to the load through the first resistor, and a second diode connected between the emitter of the third transistor and the collector of the fourth transistor; the collector of the fourth transistor is connected to the load through the second resistor, and a constant bias voltage is applied between the bases of the first and third transistors to form a single-ended push-pull power amplifier circuit. a third resistor is connected between the emitter of the first transistor and the collector of the fourth transistor, and a fourth resistor is connected between the collector of the second transistor and the emitter of the third transistor. A power amplifier circuit characterized by: