A month or so ago a guy posted a plea on the Facebook group that he had these pallets of these 12VDC, 1.5 amp switch mode wall warts and he was desperate to get rid of them or he would have to throw them in the trash. He said he would take any reasonable offer and he gave his seller name on eBay. So I thought I should help him out and I bought a couple dozen. Turned out he recognized me from the FB group, so instead of sending a couple dozen, he sent me a full carton of 84!
So I got the carton and I decided that I might be able to open them up and make a change to the resistors to lower the output voltage to 9V. When I opened one up, I found that the wall warts didn’t use the typical TL431 to regulate the voltage; instead they used a feedback winding, and in order to modify the output voltage, the number of turns of this feedback winding would have to be changed. That would be very difficult, so I had to find another way.
I’ve been getting a lot of adverts from Temu and one of them showed a buck regulator PCB that uses an LM259S switching regulator IC. They’re good for a few amps, so I bought two dozen of them. They were less than $2 apiece. Fast forward to June 16, and I received them today. They have a three digit digital voltmeter and a 10k multiturn trimmer pot to adjust the output voltage. The pcb acts as the heatsink for the LM2596 which has its tab soldered to the PCB. It uses a 47 uH enclosed high current SMD inductor. It uses a 220 uF surface mount electrolytic capacitor to filter the switched output. I recently bought some tiny 2.2 uF MLCC capacitors that have very low ESR so I can solder one or more of these in parallel with the 220 uF to filter out more of the switching pulses. Also I have a box of Fair-Rite 2673002402 RF interference suppressor sleeves that I can thread the output wires through to filter out even more of the switching pulses.
