Can I use a halogen transformer as a power supply?

Question

I have an electronic transformer which is meant to be used to drive a 12v halogen light. The specification on the electronic transformer box says 220-240VAC input, 12VAC output 20-60W.

When a 50W halogen bulb is connected to this electronic transformer the voltage across the bulb is approximately 10.5VAC.

Is there a way of using these low cost electronic transformers to supply power to a small single board computer?

Answer 1

Listen to Spehro.

If you'd rather do things the hard way, take the transformer output and run it through a full-wave rectifier. Filter the output with a large (say, 10000 uF) capacitor, then drop the resulting 15 - 18 volts through a regulator (linear or switching).

^{simulate this circuit – Schematic created using CircuitLab}

Note that the diodes must be power rectifiers, not signal diodes.

If you're planning on using the transformer with 110 VAC in, this may not work. If you draw several amps and load the transformer to 10.5 / 2 volts AC, the diode drops will probably keep the capacitor voltage too low, unless you are careful to use a LDO (Low DropOut) regulator.

Answer 2

If halogen XFMRs are PSUs (not the heavy iron core ones), this schematic may be a better alternative:

^{simulate this circuit – Schematic created using CircuitLab}

Cheers.