[Amps] Class-E Amplifiers

[ToddRoberts2001 at aol.com]

In a message dated 2/29/2008 10:14:29 A.M.  Eastern Standard Time, 
wlfuqu00 at uky.edu writes:
Class E  amplifiers have high efficiency but what about gain and drive 
power. Some  that I have see have about 10db gain but  unlike tube type 
Grounded  Grid amplifiers
I don't think any of the input power goes to the output. If  so this would 
reduce the overall  efficiency of a single stage  amplifier  and driver if 
the driver is not   Class-E.

73
Bill wa4lav  


Hi Bill,
A Class E amplifier only requires enough driving power to switch the Mosfet  
Gates on and off. The Gates are capacitive so it does require some energy to  
switch them on and off but for a Kilowatt-Class amplifier the driving power  
would only be a couple of watts. The driving power goes up as you go up in  
frequency since you are switching the capacitive gates on and off faster at  
higher frequencies so it may only need a watt or two of driving power at 160  
meters but perhaps 10-15 watts driving power at 10 meters.
 
Driving power depends on how much capacity the gates have so most people  try 
to choose low-capacitance-gate Mosfets for their Class-E amplifiers. There  
are other factors involved depending on the Mosfet characteristics but the 
gates  are basically capacitive.
 
73 Todd WD4NGG



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