Voltage Quadrupler - Capacitor and Charging Sequence question

Question

I am trying to understand how this circuit charges to 4 * VPeak. I followed the circuits for the doubler and tripler and understand both of those. I simulated the below in LTSpice and see that it works as a quadrupler. I am trying to understand the current flow and think a refresher of the basics might be in order.

I understand that capacitors pass AC and not DC. In my mind, I look at the right side of the transformer and keep ground at 0 and cycle the top side to +100 and -100. Assuming VPeak equals 100.

The first/biggest question I have...it looks like all the capacitors are polarized. If that is so, how can the capacitors on the top left be connected to AC? I understand that you cannot connect a polarized cap to AC, else BOOM!

If that is a book type, and these are regular caps, than I can think some more on this and figure how this charges to 4VPeak.

Though, it would be nice to see a dialog of what happens during each half cycle. I suspect that the right most capacitor is just there to smooth out the ripple. I suspect that to get to 4V, something gets to 3V and when you get the input positive half cycle, you get to 4v at the load.

I can probably figure that out, just the polarized caps at the start on the AC seem not so good?

Thanks for any help.

Answer 1

It may be called a quadrupler in textbooks, but it only 2x the peak to peak input voltage to a DC output voltage (minus the diode drops). the reason is the input is an AC signal so the each stage must clamp the negative waveform then the next diode can rectify it followed by the 3rd as a clamp then the 4tbh diode another rectifier.

There are four C-CR pairs (cap + current rectifiers.)

• The series Cap shunt diode is called a "signal clamp" as the diode only conducts briefly, partially charges the cap like a momentary switch.
• The series diode shunt cap is called a peak and hold detector or "rectifier and filter" or "envelope detector""

If we were to number the diodes from your image from left to right as D1,D2,D3,D4 we get voltage test points as follows;

• D1: -ve clamp
• D2: +ve Peak & Hold = Vin_pp minus 2 diode drops
• D3: -ve clamp
• D4: +ve Peak & Hold = Vin pp minus 4 diode drops

Falstad Sim

High V Quadrupler

Hi V Quadrupler that works ( with plastic caps)

Just remember it takes 2 didoes and 2 caps to make ONE DOUBLER and all the diodes are cascaded in reverse bias like a ladder

• shunt, series, shunt, series ..etc