PWM supplies, reduced to their essential parts are remarkably simple. There is the PWM chip itself, Unitrode makes a whole series, but the 3825 is particularly nice to use. It can directly drive the gate of an enhancement mode FET and provide up to 2 amps drive peak drive current at a 10 volts apporximately. Then you need the FET itself. Int. Rect. IRF740 HEXFET or equivalent for example will handle up to about 15 amps... or the IRF360 which has a peak current of ~90A. You need the transformer, which requires a core with a permeability of 1000 or more at about 10 - 30 kHZ. For max output the transformer is made with a center tapped (or a bifilar) primary winding, you just use both quadrature outputs of the PWM chip to drive a pair of FET's and connect each one in seris with one end of the transformer primary winding, and the raw DC supply positive to the center tap.
The rest ( a little HF filtering) and the core cross section depend on the exact details of your particular design.... what VA or KVA you are pushing through it.
Typically, either half wave or full wave multipliers, use about 5 to 10 kV peak voltage for the stage voltage. Thus what your PWM drives will require is an appropriately wound secondary. Assuming you use a sufficiently large core area, (a few sq cm will give you a a few hundred watts capability at 20 KHZ) then you should operate at about 0.5 to 1.V per turn, which will point you in the right direction as to how many output turn you need.
The multiplier will require capacitors having enough charge storage so that at the frequency it operates, a sufficient stage current passes through to power all the stages beyond. Common cap sizes are a few nF at a few kV per stage, whether half wave or full wave. The HV rectifiers need also to be fast recovery (<100 nS) so that you don't get reverse voltage breakdowns.
Obviously, the DC supply has to be equal to all this so if you are looking to put a KVA output from your transformer... you will need a serious LV supply.
Hope this is somewhat useful.
Dave Cooper
Created on Sunday, March 25, 2001 9:08 PM EDT by David Cooper