Replacing a 87D-24S05RT12R (obsolete) with a Murata TWR-5/3000-12/500-D12A-C
Breadboarding before I install, I’m having trouble with the +/- 12 volt outputs.
As soon as they are loaded, they drop to about 8 volts. They float at about 16 volts unloaded. The 5 volt supply tests at a solid 4.9, loaded or unloaded. I’ve tried input voltages from 9v-36v with virtually no change. Digikey replaced it once already thinking it was defective, but the new one behaves exactly the same. Any idea what I’m missing here?

Hi EmiAudio,

Under what load conditions on the 5V output did you test the +/- 12V outputs? Since they use a common transformer, loading (or not loading) on the 5V output can affect the other outputs.

The 12volt outputs do not show any significant change in output when 5volt supply is loaded. I have loaded the 5volt supply to about 100ma on the bench.

This looks like a similar issue to the one discussed recently in this thread..

The issue is that the multiple outputs are often developed by using different windings on the same transformer; feedback to regulate output voltage gets taken from the primary (highest-rated current or power) output, and regulation of the others happens as a result of the winding ratios in the transformer.

Without a sufficient load on the primary output, the auxiliary outputs can sag significantly because they’re not being monitored directly; the supply just sees a nice, well-filled output capacitance on the primary output, and sort of assumes they’re in regulation when in fact they may not be.

It’s a fairly common behavior, though one which is perhaps not so clearly stated in a lot of product literature.

I suppose that could be it. Do all 3 channel converters behave this way? I was looking at this one from Mouser. It will also be a physical match.

It is not necessarily so but it is quite common, especially among relatively low-power, compact units such as this. I expect the item you mention (which by the way is DK part number 102-2954-ND) would exhibit a very similar behavior, due to the output regulation specs coming with minimum load and load balance qualifications.