The product pictured is the current generation PL380. When I left QSC I was wrapping the Class D amplifier stage for what at the time was called the PL260 with the same specifications. I believe the PL360, which was released soon after my departure, incorporates all or most of my power stage and went on to become the PL380.
Description:
This power stage was what I cut my teeth on with regard to large power Class D amplifiers using the technology available at that time. Up to this point I had designed several smaller power (several hundred watt) Class D amps as R&D projects. Back then, floating high voltage driver ICs were not available and we had to use high speed optocouplers to do the level translation. This design was based on a naturally sampled, fixed frequency Vanderkoy modulator and a three device per leg output stage to overcome the recovery losses of the high voltage MOSFETs available at that time.
Innovations:
My largest contribution to this design was the modeling and optimization of the control loop to maximize loop bandwidth and loop gain. Devices were relatively slow at the time and the added complexity to “get it to work” added substantial delay, dead time and subsequently distortion. Getting a solid handle on the control parameters and how to optimally adjust them was critical in achieving the noise and THD figures the specification demanded.
