Naked Science Forum
Non Life Sciences => Technology => Topic started by: suryatej on 05/03/2009 10:53:55
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how to get a variable supply from -20v to 20v as output from a single battery of 9volts ..is there any ic or cicuit for that...
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Yes - it's called an DC-DC converter. What you have to do is to produce some AC from the 9V DC source, then transform it to a higher voltage and rectify it back to a new voltage of DC. Nowadays, it may not be done with conventional transformers but that's what is done, effectively in modern switched mode systems.
For your particular requirement, it would depend upon how much power you needed from your +20 V to 20V supply and how much power your 9V source could supply.
12V DC to Mains voltage inverters are readily available and so are variable PSUs but I suspect that wouldn't suit your application. More info needed.
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There are some simple easy-to-use ICs which will give you a negative supply rail from a positive one (using a flying capacitor arrangement). I can't remember any part numbers, but the cheap ones are good for a few mA, maybe even 10-20mA.
In general though, and especially if you need voltages much more than 2-3 times the original supply voltage, then as sophiecentaur said, you need an oscillator (to make crude AC) and a transformer. Typically these days you use a small ferrite-cored transformer operating at a few 10's kHz. You can generate several hundred volts that way, if you want, and is what they use in handheld fluorescent torches for example.
If you really need a variable supply then you'll need some regulation and it all begins to get more complicated.
You should also consider that a PP3 9V battery doesn't have much current capability or very much total energy so may not be so practical for a general-purpose supply anyway.
Different techniques would be best depending on the power levels, efficiency requirements vs simplity etc etc. Give us a better idea of what you're trying to achieve.