Class C Amplifier

407

06:01:15

Typically this kind of amplifiers have a lot of inherent distortion because they work in the linear part of their characteristic a very small amount of the time (only at peak moments). Usually the output will be very distorted but applying an LC filter restores the signal perfectly and amplifies it. This is an RF power amplifier because it amplifies both current and voltage. The output power is 2W the transistor being 2N3553. The input power is around 200mW.

published 10 years ago

faceblast

10 years ago

it seems limited to the resonance of the filter? if i change the freq to 30MHz the output is still 95MHz

thebugger

10 years ago

Well yes thats the most distinguishable feature of a class C amp. It works in a very narrow frequency range (the resonance frequency of the tank circuit). But that's what restores the original undistorted signal. Try changing the LC filter with a resiator and check out the immense distortion levels. That's because the transistor is not biased and only a fraction of the whole wave gets amplified. But that's enough for the filter to restore the fundamental frequency with very small distortion. This kind of amps are generally used only in RF applications and not in AF because the filters would be very big (because they should respond to lower frequencies) and wont be able to restore the complete signal because they worl in a very narrow frequency band. For audio applications class A B AB D should be used for RF Class C and maybe class A for the preamplifier.

thebugger

10 years ago

The output will still be around 90Mhz because 30Mhz is a subharmonic of 90Mhz and will still do the trick. But this way it should be amplifying a lot of harmonics. Try 32-33Mhz where it's closer to that harmonic but you'll be wasting a lot of power on harmonics.

thebugger

10 years ago

Imma try and design a transmitter with this kind of power amplifier to better demonstrate it's features.

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