[sdiy] converting circuits to work with lower voltages

[Roy J. Tellason]

On Monday 17 January 2005 03:07 pm, Milo Barrowclough wrote:
> hi everyone
>
> there are several cicruits that i would like to build, but they all require
> + - 15 volts. is there anyway to modify the circuit so that it will work on
> lower voltages such as +9 -9 volts e.g. two 9-volt batteries?  maybe i
> could reduce each resistor value by a ratio or something.

Depending on what the circuits are,  you may not have to make any changes at 
all,  as most of what I can remember seeing in assorted schematics didn't 
have much of a dependency on an absolute set of power supply voltages.

You _will_ see a reduction in the dynamic range of the signals you can handle, 
though.

And,  I wouldn't expect to get much life out of 9 volt batteries,  they're 
just not made to supply all that much current.  For something that I wanted 
to run at 9 volts that had some nontrivial current requirements,  I'd go with 
a stack of C or D cells.  FWIW,  the battery chart I mentioned earlier shows 
a "typical drain" of 15 mA,  which isn't much.

You go buying those many batteries all that often,  and you'll end up spending 
enough after a while that a power supply would end up costing less.  Unless 
you *really* have a requirement for portability...