All existing audio amplifiers are AC coupled to prevent DC
signals from damaging speakers. The amplifiers can do this
because speakers have natural spring-damper characteristic
which returns them to their center position and pressure
waves do not rely on any DC position for transmission.
Our control strategy, however, may want to control steady
state fuel flow as well as high frequency fuel flow thorough
the nozzle. The amplifier above was built to test the
feasibility of building an amplifier for such an application.
The amplifier in the above figure measures a flat input-output voltage response at 200+ Watts from DC-20Khz into the 4.7 ohm voice coil. It does so by driving a pair of Hitachi (2SK1058/2SJ162) L-MOSFETS with an APEX high voltage Op-Amp with external phase compensation. The Op-Amp is externally phase compensated to account for the high gate capacitance of the MOSFETS. The configuration above should be capable of easily driving a bank of 10 MOSFET pairs and thus 2 kW into the load.