Current driven Output-stage class AB power amplifier

Author(s): Hegglun Ian

This article covers a simple modification that overcomes most of the tricky thermal stability issues of regular Class-AB output stages. It uses a common emitter power output stage to remove the power transistors from the Class-B current splitting process. That’s the first step. The second step is to remove the base-emitter resistors across the power transistors. This method is not new; it was used in the Practical Wireless ‘Texan’ in 1972; Ian’s Square-law Class-AB and Win de Jager’s ‘New Class-B’ design in 1999. The well-known Blomley used the first step (current splitting) but not the second step due to slow power transistors, which limitation is no longer valid these days.