SDG #132 A Low Cost 2 Channel AC-DC Power Supply Board

Dual rail supplies are one of those awkward requirements in analogue and audio work: you need a positive and negative rail, ideally isolated from mains, without paying a lot for a linear transformer and rectifier assembly. This episode looks at a very inexpensive two channel AC-DC switching power supply board aimed at exactly that gap, along with a companion negative output module that lets a single positive rail be inverted for split supply duty.

The assessment goes well beyond checking that the LEDs light up. Construction quality gets scrutinised first, since that is where budget mains boards usually cut corners: creepage and clearance between the primary and secondary sides, whether an input fuse and any transient protection are actually fitted, the quality of the transformer isolation, and how the two channels are derived, either from separate windings or from one winding with post regulation. That last point matters more than the spec sheet suggests, because a shared winding means loading one output can pull the other around.

Electrical testing covers what buyers actually care about: load regulation on each rail, cross regulation between channels, output ripple and switching noise measured properly rather than with a long ground lead, and thermal behaviour when the board is asked to hold near its claimed rating for a sustained period. Advertised current figures on modules at this price are frequently optimistic, so headroom is treated as an unknown to be measured rather than trusted.

The verdict is framed around suitability. A board like this can be genuinely handy embedded inside a project enclosure or powering low current op amp and preamp circuitry, provided the noise floor is acceptable and the mains side wiring is treated with respect. It is not a substitute for a properly certified supply, and expectations about the negative rail module should be set by measurement rather than marketing.