12 January 2015

(27 y.o.) PSU update

The aforementioned LED strip in the shack needed a 12V power supply. Since I had wanted to turn one of my fixed PSU into variable (or multi-output), I jumped in and applied the mod.

The chosen unit is my "rms K132" linear PSU:

It contained a 7812 regulator produced in mid 1987. Since it never needed a repair, the unit should be ~27 years old! That's when I started on 27 MHz Citizen Band. I remember the price was a linear function of amperage: 2A = 20'000 (good old) Lire; 5A = 50'000 Lire. By the way, 20000 L@1988 ~= 20 €@2015.

The idea: replace the 2A 7812 linear regulator with an adjustable switchng board of equal continous current capacity. I used a board based on LM2596-ADJ and it fits comfortably given the large PCB and the amount of free volume inside the PSU.

One more change was to replace the red LED with a yellow one, as a warning sign that the PSU is NOT 12V anymore.

For the LED strip I tuned it down to 10V, and I probably go even lower. The FT817 receiver does not complain of this switching PSU since there is no added noise vs my usual RTX PSU.

DISCLAIMER. This operation was made inside an high-voltage AC unit. ALWAYS disconnect the power cable from the AC socket and dischage the large capacitor before touching anything inside it. I will not take responsibility for injuries or damage to anything/anyone if you decide to replicate or reproduce what I have shown above.