MOSFET power amplifier

7-96 g D MOSFET power amplifier The output power of an operational amplifier is often increased by a com- plementary emitter follower. It can also be done with a MOSFET, but it is not a good idea to connect such a device as a complementary source follower because the maximum out- put voltage of the opamp is then reduced appreciably by the gate- source control voltage of the MOSFET, which can be a couple of volts. R3 100k Another approach is to connect two MOSFETs as a complementary drain follower. The (alternating) output cur- rent provided by the MOSFETs is limited by the level of the supply voltages and the saturation voltages of T3 and T4. Resistor R8, together with R9, provides feedback for both the opamp and the MOSFETs. The open-loop amplification of the opamp R1 is, therefore, increased by (1 + 88/88). The closed-loop amplification of the complete amplifier is (1 + R3/R2), i.e., JJ.9" 11. The current source formed by T1and T2 is required for arranging the quiescent current ...