12 volts from a 9 volt power supply...

[kissack101]

Is there any way of doing this? I've searched through all the old posts, it seems that getting 18v (and higher it seems) is do-able, but from my searches its not clear if you can get voltages that aren't multiples of 9? Is 12 volts possible if I built a 9-->18v circuit and then somehow limited the voltage?

Any help would be much appreciated.

Adam.

[Brett Sinclair]

Well you can use a MAX1044 charge pump to get 18V and then regulate it back to 12V using a 78L12 (see the PT-80 schem on GGG how to do that).

[kissack101]

Hey, yeah I was thinking of something similar. I've only used voltage regulators once though and I seem to remember it getting very (worryingly!) hot very quickly so I disconnected it. Does the voltage/current ratio remain the same before and after conversion? How much current would be lost in the conversion process?

Adam.

[d95err]

Hey, yeah I was thinking of something similar. I've only used voltage regulators once though and I seem to remember it getting very (worryingly!) hot very quickly so I disconnected it. Does the voltage/current ratio remain the same before and after conversion? How much current would be lost in the conversion process?

You can put a small heatsink on the voltage regulator to keep the heat down. I assume Ohm's law would still be valid, so you would loose half the current capacity when doubling the voltage. E.g. if you have a 9V supply that can handle 500mA, you should get about 250mA at 18V (actually a bit less since there is probably some loss in the conversion). When you take it down to 12V, you still get max 250mA 12V. Since the voltage drop is 6V, the regulator would have to dissipate 6*250mA = 1.5W

Seems like a very complex way to do things. Are you sure you can't get a 12V supply to begin with, or use a 12V battery?

[kissack101]

Yeah, a 12 volt power supply seems to be the way forward. I was hoping I could get away with 9 volts as it seems to be more common for guitar pedals but I think the current loss will be too great in the conversion process.

So when you take it down to 12v, its not so much a 'conversion' process as it simply expends the excess voltage before it enters the circuit? If a heat-sink is necessary, I don't think this one is a go-er, thanks anyway though...

[stm]

Take a look at the MAX761.  If you provide a small inductor (in the 22uH range), a shottky diode and a couple of capacitors you can get 12V with supply voltages as low as 3V.  This means you can fully deplete a 9V battery and still get regulated 12V.  This IC allows also getting other voltages by means of an additional pair of resistors, up to 16.5V, so you can also provide 15V to those MN3007 circuits for maximum headroom and S/N ratio, or even regulated 9V regardless of your battery condition.

I believe there is also an inverter in this family which should allow you to get regulated negative voltages as well.

[R.G.]

It's entirely possible. In fact, you can get any voltage from any voltage - if you want to work hard enough.

There is one easy way of getting 12V from 9V. As discussed, upvert with a charge pump to +17-18V and then linear regulate down with something like a 7812 or LM317. As you noticed, Mother Nature was trying to tell you that this is not a very efficient way to do the job, and a lot of electricity is wasted as heat.

The other obvious way is to build a regulating switching converter to suck current through an inductor, then let the inductor flyback voltage pump it up to +12V. This used to be hard to do, but modern ICs make this a one-IC job. It's highly efficient, but suffers from pulling high and fast pulse currents that can interfere with audio if you're not careful about layout and decoupling.