Explanation of Operation of Class E Amplifier Circuit

Question

I am looking for a good explanation for the operation of a Class E amplifier circuit (example below from Wikipedia - picture from Yves-Laurent Allaert)

As will be evident by this description, my understanding is rudimentary. I believe I understand that if you just took an LC tank circuit and injected a pulse of DC, AC would be generated in the tank circuit for a little while until the energy is dissipated through whatever resistance is in the components or load.

In the picture above, with the switch open (or without the switch), it seems like something similar would happen where current would flow into the LC circuit and you would see AC across the load. When the switch T1 is closed, maybe some current is diverted through the switch but there would still be some current in the tank circuit oscillating.

So is the switch just there to "shape" the waveform across RL?

Is there someone that could just provide a basic explanation of how this works? I tried to simulate this in the falstad circuit simulator but couldn't quite come up with the correct LC values, etc. to see how the switch impacts the AC across RL.

Answer 1

With switch T1 open, and applying VCC, you would initially see current ringing around in the resonant circuit until both C and Co are charged up to Vcc. The ringing would diminish as the energy is dissipated into RL. Then the circuit would remain in the capacitor charged state.

By closing switch T1, you are connecting L1 across the total Vcc (storing energy into L1). At the same time the resonant portion will begin to discharge thru T1.

When T1 is opened, inductor L1 will discharge it's stored energy into the system, thus RE-charging the capacitors.

One cycle is complete at this time. The repetition rate of closing and opening T1 determines how much power is delivered to RL.

The time for T1 closed determines how much energy will be stored in L1.

For simple power producing, capacitor C could be replaced with a diode whose anode is connected to ground.

Answer 2

Yep! The switch effectively controls the output waveform, both in terms of frequency and amplitude. The DC pulses it generates are smoothed into AC by L1 and C1 and the output filter (the RLC circuit). Keep in mind the switch in the diagram is just a representation, in practice that would be some sort of digital switch controlled by a PWM driver. As for actual values for the filter components, that will depend on what you want the amp to do.

FWIW, I assumed that by basic you're looking for a fairly simple explanation. If you want a more general (or specific) idea of any aspect of how class E amps work ask away.