+/- 15v pibolar supply question.

[Martin Czech]

:::is it possible to use two 15 v wall warts in combination to obtain a
:::bipolar supply, as such:
:::                         ________ + 15 v
:::              + --------|
:::  wall wart 1           |
:::              - --------|
:::                        |-------- ground
:::              + --------|
:::  wall wart 2           |
:::              - --------|________ - 15 v
:::
:::(with appropriate .01 uf capacitors to buffer the power supply)...
:::
:::Or will this thing just short circuit and melt?


If the wall wart contains only a transformer this will work, given that
you connect the windings in the right order (wrong order means voltage
cancellation, but no destruction).

If the wall wart contains also rectifier and electrolytics, this is also
possible. In fact, many big power supplys use two transformers and two
rectifiers in the way seen above in order to get parts with the needed
power ratings.

If the wall warts have regulators inside, well it should work, and some
regulator data sheets have applications like that, but I'd be carefull.

If you're not sure you could try to connect the two warts with 0.25 Watt
metal film resistors starting with, say 100 Ohm and the decreasing to
1 Ohm or so, always observing. This is an old trick to power up "hot
circuits" for the first time. If exessive current flows, the resistor
will blow up, and that's it.

m.c.