Direct Coupled Class AB Output Stage:

The output capacitor in a capacitor-coupled power amplifier is a large expensive component that should be eliminated if possible. Figure 18-23 shows a Class-AB amplifier circuit with a Direct Coupled Class AB Output Stage.

In this case, the supply voltages must be positive and negative quantities, +V_CC and -V_EE as shown, so that the dc voltage at the output is zero. This is necessary to avoid a power-wasting direct current through the load.

Apart from the positive/negative supply, the direct-coupled circuit operates in the same way as the capacitor-coupled amplifier.

With a few exceptions, the design procedure for a direct-coupled circuit is essentially the same as for a capacitor coupled circuit.

Equation 18-15 gives the total supply voltage, and this must be halved to give +V_CC and -V_EE for the direct-coupled amplifier. The total supply voltage must be used to calculate P_i in Eq. 18-17. Also, the transistor maximum V_CE is the total supply voltage.