Category A and B output circuit using diode coupling

The diode- coupled Class A and B output stage circuit is shown in Figure 10-8. When in static state, adjust the bias circuit of VT1 (not shown in the figure)
so that the output terminal E point to ground DC voltage UE=o. The forward voltage drop of VD1 is added to the emitter of VT2 and VD2, making VT2 in a micro-conduction
Class A and B working state.
    When the input signal U is a positive half cycle. The collector current of VT1 increases, and the voltages of points B and C to ground decrease. The voltage drop at point B causes
the emitter voltage of VI2 to drop and cut off, and the voltage drop at point C causes VD2 to completely conduct. then. RL, VD2, VT1 and - Ucc form a
path, and the current Tuen flows through RL from bottom to top to form the negative half cycle of the output. Because RL <Rt, the collector signal current of VT1 is iCl—/L. When
the input signal U is a negative half cycle, /c decreases, and the voltages at points B and C increase. Therefore, VT2 is turned on and VD2 is turned off, and +Ucc, VT2
and shame form the positive half cycle of the output signal. It can be seen that VD2 is equivalent to a gate, and the opening and closing of the gate is controlled by the change of the positive and negative half-cycle voltage of the input signal
. in actual circuits. VT1 and VT2 generally use composite pipes.