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Registered Member #29
Joined: Fri Feb 03 2006, 09:00AM
Location: Hasselt, Belgium
Posts: 500
Hi all, After digesting some of the models presented in Sokal and Grebennikov's book on Switch mode RF Power Amplifiers, I put together a a set of design equations for Class-E amplifiers. You can find this on om Class E amplifier page. The document link is here.
Hope it is useful! It utilises an ideal switch assumption, but you should be able to generate an initial design for tweaking when using real transistor switches....
Registered Member #1232
Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881
Do these equations only guarantee that the collector (drain) voltage goes to zero at the turn-on instant?
...OR do they also guarantee that it lands smoothly at zero volts with zero gradient (dv/dt=0) as well?
Many seem to quote only the first criteria as a requirement for efficient Class-E operation. This means the voltage can slew rapidly through zero around the turn-on time. However, I beleive that the soft landing is important for two reasons:
1. A dv/dt across the shunt capacitor of zero implies no current flow at that time. This ensures both ZVS and ZCS of the switch at turn-on. Therefore minimal switching loss at turn-on.
2. A soft landing of the switch voltage at the point of turn-on also allows for some latitude in the tuning of the Class-E amplifier. i.e. If the transistor is turned on a bit too early or a bit too late, the voltage will still be lingering very close to zero volts. Therefore, the amplifier is "broadband" to some extent.
Registered Member #29
Joined: Fri Feb 03 2006, 09:00AM
Location: Hasselt, Belgium
Posts: 500
Yes, the equations guarantee that both v and dv/dt are zero at switch turn-on time. This is one of the basic, initial assumptions: it is the definition of Class-E operation.
The output circuit Q controls the bandwidth over which we can operate near this ideal switching point.
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Class E amplifier design rules
