Hi-Fi MOSFET Amplifier with 100W Output

The project was built around the Hitachi lateral power MOSFETs to create high fidelity Class AB amplifier.

Most power MOSFETs use a vertical structure where the current flows vertically. The gate oxide of lateral MOSFETs is formed on a flat substrate and the current flows across the substrate resulting in well defined, controllable device parameters, good linearity, and relatively low gate capacitance. MOSFETs also have high input impedance at low frequencies and are capable of extremely high slew rates. They do not experience the problem of thermal runaway like most amplifiers do due to the increasing gain of bipolar transistors which causes it to get hotter and results to passing most of the current to the hottest.

A 28V RMS is needed across the load in order to dissipate 100W in 8 Ohm speaker. This will give 40V peak while the amplifier requires 5A supply at the peak. Two pairs of drivers are needed for the MOSFET to be around 10V at high current which will signify that the supply must be at least 10V greater than the peak output voltage. With a peak secondary 56V, a twin 40V transformer is appropriate.