In my never ending quest for a cheap and simple high voltage regulation I have come up with a simple dual capacitor mode. This is similar to a Buck circuit without the inductor.
The concept is simple: One capacitor is charging to the pre-destined voltage while the other is discharging into the load. These are simple RC circuits and the time constants are readily known. The load is not connected directly to the load because it will potentially see high transient voltages from the supply. Also the capacitors are charged at a rate close to what it is being discharged by the load. This is to reduce switching frequency and rise/fall times.
The switching is done with make before break on the inner two so that the load is never disconnected from a capacitor. Alternatively one could simply use one side with a capacitor in parallel with the load to supply the current while the other capacitor is charging. Either case will work but I have specific reasons for choosing the first case.
My main concern is driving the mosfets so the gate voltage is within spec. In fact I'm not quite sure how to do this.
My requirements is a programmable constant voltage supply from around0 voltages to 1kV driving a load of around 100kohms to 1Mohms. The regulation should be less than 1% or better.
From my calculations I easily get less than 0.1%. i.e., t = -R*C*ln(Vc/ V) and for R = 10^5, C = 10^(-5), Vc/V = 1 +- a/100 where a is the percent regulation gives about 1ms for 0.1%. Hence discharging the capacitor into the load will drop approximately 0.1% of its voltage in1ms.