Complementary symmetrical push-pull circuit

Although the Class A power amplifier circuit has low distortion, its efficiency is low and the output power is small, so people designed
the Class B power amplifier circuit. The Class B power amplifier circuit moves the operating point Q from the middle downward to the position of Q2, that is, in the static state, the base of
the transistor has no bias current, b=00, and the transistor is turned on only under the action of the input signal. The
amplitude of the maximum collector current when it is operating is much larger than that of Class A output . But it only works during the positive half cycle of the signal and does not work during the negative half cycle. This causes serious distortion of the output signal . For this reason, the Class B power amplifier circuit adopts a push-pull output working mode, with two output tubes working alternately, as shown in Figure 1-140. This circuit consists of an NPN tube Vtz and a PNP tube. Composed of tube VT3. In the positive half cycle of the signal VT. 3 tubes work, and the VT2 tube works in the negative half cycle of the signal. The two output tubes output the positive and negative half cycles of the signal respectively. Finally, a complete output signal is synthesized at the total output terminal . Since the circuit uses two different polarities The transistors complement each other's deficiencies, so this circuit is called a complementary symmetrical push-pull output circuit .