This article documents the build of an inexpensive regulated power supply available on the Internet for around A$15 posted.
Above is the completed power supply (with some modifications as discussed below).
A bit of reverse engineering
It is sold without any form of technical specification. We can guess at its current capacity from the 1000µF filter capacitor, for 2V ripple I=CV/t=1000*1e-6*2/0.01=0.2A, though it probably does not have the headroom for 2V of ripple, diode voltage drop and transformer sag at 12V output.
Above is the assembled PCB. Board quality was good, fitup was good apart from the display which was a bit of a squeeze. A little thermal grease (not supplied) was used to mount the regulator, but as will be seen, heating was not an issue.
Above is the underside of the PCB after assembly, cleaning and lacquering.
Perhaps surprisingly, the little voltmeter was quite accurate, <1% error at 5V.
Maximum current obtainable (mains at 255VAC):
- 0.03A @ 12.0V; and
- 0.2A @ 5V.
Clearly, the power supply filtering and transformer sag will not support much output current.
Above, a thermograph of the supply after stabilisation on 0.2A load @ 5.0V (Tambient=25°). The regulator heat sink (lower right corner) does not warm up significantly, and the transformer heat rise is quite modest.
A fun little project to build. As supplied, it does not meet our safety requirements and rework of the mains cable is needed.
The acrylic case is quite fiddly to assemble, orienting the nuts is a PITA.
Current capacity is very low, but it could be a handy little variable power supply for the experimenter.