fatheaddrummer said:
Can anyone tell me how the principal of a voltage tripler works - step by step, what is really happening? I don't really get it and cannot find something useful in the internet about that.
Thank you so much!
Christian
OK step by step...
#1 understand the basic components.
A diode only passes current in one direction. A (relatively large) capacitor passes AC current in both directions.
#2 divide and conquer.
First stage C1 and D2.... The input labelled + is really an AC signal that swings + and -. The unlabeled input lead connected to the cathode of D2 is ground or 0V. As the AC signal at the input swings + and - the cap output tries to follow, but when the right or negative end of C1 tries to swing positive, D2 conducts and clamps that terminal to approximately 0.5V positive. However in the negative direction the diode does not conduct, so the cap swings freely in the negative direction. After a few cycles the output side of C1 is swinging the same AC voltage just shifted negative by a DC voltage equal to the peak input .
The next stage is C2 and D1. The left positive end of C2 is connected to 0V so does not change. The negative side of C2 is connected through diode D1 to the output of the first stage. Since diode D1 conducts when the output of the first stage swings negative, capacitor C2 gets discharged down to -2x the input peak voltage.
The final stage C3 and D3 has C3 connected to the output of the first stage that swings the full AC voltage just shift down by the rectified DC voltage. Diode D3 biases the output side of the cap C3 down 2x the peak DC voltage so 2x DC bias + 1x from the AC swing generates the 3x voltage tripler.
The output of this tripler is still an AC voltage so you need another cap and diode (like the second stage) to extract a DC voltage from this. In fact you can stack any number of stages to generate Nx multipliers.
There are a number of other practical considerations when trying to pull significant output current since the simple tripler will pull 3x the output current in the input stage.
These circuits are popular for making low current higher voltage supplies like 48V phantom that only draw a few mA.
JR