charge pumps

[jbm222]

The geofex article where i first discovered how to use a charge pump to get higher voltage out of a 9v power supply suggests usings 10uF caps.  It works with just about any value or type of capacitor (I tried ceramic, film, and electrolytic ranging from .01uF to 100uF).

Intuitively, it seems like a larger cap value would for higher current draw (peak values anyway) and eliminate more of whatever rectifier ripple remains.  So would it cause any problems to use 100uF instead of 10?

Also, the article recomended not connecting the power supply ground to the signal ground.  How does this work?  Using the highspeed chip (the one that smallbear sells), would there be any need to do this since it pulses at a frequency well above audible range?

[jbm222]

bump.

[aron]

I believe I used this circuit (shown on bottom of this page)

http://geofex.com/circuits/+9_to_-9.htm

I'm not sure about the caps.

Aron

[gez]

Intuitively, it seems like a larger cap value would for higher current draw (peak values anyway) and eliminate more of whatever rectifier ripple remains.  So would it cause any problems to use 100uF instead of 10?

I've messed around with 'home grown' 555 charge pumps and increasing the cap value (I was thinking along the same lines as yourself) didn't really change anything, they can only charge the cap at a certain rate so have a finite amount of current they can source (think that's right).  

Ripple isn't really a problem as the chips are run at frequencies well above audio.

I'm no expert on these things, just my 2 pence worth...

[bassmeister]

Another trick is to use the MAX232. It's not intended as a charge pump circuit (it's a TTL-to-RS232 bus transciever), but you have +10 V and -10 V on pin 2 and pin 6, respectively. Some drawbacks vs. the MAX1044 though:
- Larger pin count.
- More components (external capacitors).
- More expensive.

Also I can't tell how much current that would be available. The MAX1044 is a better choice, but it might be worth trying if you already have the circuit lying around.

[gez]

R Penfold uses power ICs as 'step up' charge pumps.  Because they don't have rail-to-rail output swing you won't get double the supply, but from 9V you could probably get somewhere in the region of 12-14V.

You'll get a hell of a lot more current from these things...