Charge pump theory

[IO390]

Hi all,

I'm planning to design a DC charge pump to drive nixie tubes (9v-170v), but I can't find any proper explanation of how the things work anywhere.

Can someone help me on this?

IO

[mmilejski]

Dave actually recorded pretty nice video about voltage doublers so you might check it out Here is a link:

[lewis]

You might struggle getting a charge pump to output that kind of voltage at reasonable current. It's probably simpler to use a boost converter - have a look here: http://www.dos4ever.com/flyback/flyback.html

[NadAngel]

Yes, it is hard to deliver that kind of power with a charge pump. If you want to boost the voltage from 9 V (RMS) to 170 V (DC) with a CW charge pump you would need approximately 14 stages using this equation (if we forget about the voltage drop due to the load current and forward voltage of the diodes).

Eout = Ein * sqrt(2) * n

Each stage consists of two diodes and two capacitors. In your case you would also have to take into consideration the total voltage drop of all diodes, that would reduce the output voltage. You also have to know that the output voltage drops with a higher load current.

Vdiode_drop = 2 * n * Vf

Vdiode_drop is the voltage drop of the diodes
Vf is the foward voltage of the diodes
n is the number of stages

Vload_drop = I / ( f  * C ) * (2/3 * n³ + n² / 2 - n / 6

Vload_drop is the voltage drop
I is the current drawn in amperes
f is the frequency in hertz
n is the number of stages
C is the size of the capacitors used in farads

In conclusion, CW multiplier is not practical for applications requiring high output currents and high number of multiplication stages. You would get better results using a standard boost converter or a transformer.

[ajc]

A simple / cheap option is to go for something like this design based on the 555 timer - http://www.ledsales.com.au/kits/nixie_supply.pdf

I've used charge pumps in the past to provide a simple +/- supply but the current delivery capability is pretty low as the output impedance is generally pretty high and I'm only talking about using a charge pump to do simple voltage doubling.  9v to 170v is another story...