Class-E amp

Firstly, like a class-C amp, a class-E amp can only work well at one specific frequency, so the component values will be tuned for that particular frequency. Also, for a class-E to work it needs to be loaded with the right impedance, otherwise it won’t work well. Class-Es are usually used for radio purposes, so a 50Ω load is good since most antennas have a 50Ω impedance, and if the antenna has a different impedance, a balun (a transformer) can be used for impedance matching. So that means the load resistor should generally be 50Ω. Now for the waveform. The blue waveform needs a specific shape: it should reach 0V right when the MOSFET switches on in order to avoid unnecessary power dissipation (in fact, class-Es have a maximum theoretical efficiency of 100%, just like a class-D audio amp, so any wasted power whatsoever is unwanted). Also, in order to maximize output power the blue waveform should be flat right as it hits 0V and the MOSFET turns on. This isn’t so important though, but it’s much better to have it still sloping down than for it to have already reached a minimum and then slope up to reach 0V, because that means it’ll go negative which will cause the MOSFET to act as a diode which will then dissipate some power.

Now for the actual values. The inductor at the power supply is almost always a high enough value that it’s essentially a constant-current source. For this purpose 1mH will work well. For the other values, I was able to use trial/error to determine that the capacitor next to the MOSFET should be 2.2nF, the other capacitor should be 22nF, and the inductor should be 47μF. This is with a 50Ω load. With these values it hits 0V right as the MOSFET switches and when it does hit 0V it’s almost exactly at it’s minimum. In fact, I’m surprised at how perfect it is. However, the output waveform isn’t quite as perfect. In fact, it’s quite far from a perfect sine-wave, which is bad for radio transmission since it means the signals can be picked up at multiples of the transmission frequency where other stations might be broadcasting. The only way to fix this is with a more advanced filter. What I’ve done in my class-E amps is used a series of inductors with the wire between each inductor connected to ground through a capacitor. I then tuned the inductors and capacitors to have a cut-off just above, or even at the output frequency of the amp (usually for simplicity’s sake all the inductors in the filter have the same value, and same for the capacitors). Of course, with the addition of the output filter, the rest of the components will need to be re-tuned.

Here’s a class-E of mine with an output filter: http://everycircuit.com/circuit/6122692830035968

Yup; I saw your class-E amp. I understand how the circuit works (hopefully, wikipedia helped me) but I am not satisfied with a 1mH inductor as it doesn't block a large amount of HF AC signal. That's why I starter to use 5mH but it causee it's own problems. Earlier before the circuit was published, I had made a trial version with a 2.2mH choke and the rest of the components chosen arbitrarily. I also found out that the FET should switch at the right time, when the drain voltage is almost 0V. I used the resonance equations but it doesn't work here; how can we design a class e with the appropriate approach, giving us the exact values? I found an online calc but how the heck can it be useful without knowing how to design one? Thanks @jason9. How did u get the typical values? Seems that bugger used common component values of class-e amps.

How can I make the LC circuit (the output side of a typical class-e amp) resonate with the input? Idk why the resonance equations cease to work. A day back, I found this circuit of yours. It's from this that I figured out to use a load at the output which has a low impedance. You also seemed to have used transformers for impedance matching. But the intriguing thing was the filter; will the filter generate unnecessary phase shift or will it transform the output impedance to a new value? That's the actual set of questions I had (sorry that I didn't make it much clear in my circuit). Thanks for typing out that big explanation.

Oops; sorry for the choke value. Idk why I changed its value from 2.2mH to 10uH. NVM.

Rather than treating the filter as an impedance and working with that, it works best to simply re-tune the components until it works correctly again.

Also, while there are almost certainly equations (as indicated by the existence of online tools) I don't know any of them or where to find them.

Tuning this till it worked should've been pretty exhausting. I hope that I'll not hop into the equations coz they involve calculus and all, waaay advanced. However trial/error didn't work for me. Stuck in the middle of both. Had bugger told you anything about the design of class e amps?

A filter having a 69uH inductor, a series cap and another cap across which the output is to be taken from is a bit weird; a class-e amp (okay now this's from my interpretation, dunno if it's wrong) has the FET switching at the resonant freq of the LC circuit, with the choke providing the positive voltage to resonate such that the power dissipation is low. How can you determine the output filter values coz it interferes with the a actual resonant circuit? A tri-pole filter like this can be used to transform the impedance at the output (I had seen bugger mention that in one of your circuits) just like a balun does. Dunno how you managed to get it to work with this filter at the output.

P.S. I notice that all of both your class e circuits have nearly equal component values, except one in which the values are pretty random.

Here's a class e amp calc:- http://class-e.sigenics.com (site not so secure)

I remember the first time I tried to figure out the values of the class-E components I had difficulty too, but now I’m pretty good at it. I also figured out today from experimentation that the 69μH inductor can be any (reasonable) value and simply tuning the capacitors is enough to achieve the desired waveform.

Also, in order to make it work with a filter, I just tacked it on between the load and the rest of the amp and re-tuned the amp component values.

P.S. I've managed to get the class d amp to work!

Finally I made it.