I'm having an issue with some cheap BUCK modules that aren't doing what I've expected.
unregulated 24VAC output of a main transformer.
Tested, the transformers unloaded output is about 28VAC.
8.5V @ 120mA (Completed circuit at max continuous draw)
(There is a 5V linear reg in my circuit.)
Module in use: LM2596HVS
This appears to be the same module.
Cap. Ratings are the same.
My Inductor is a 470uH, the one in the listing is 330uH.
From reading the switcher's datasheet, my needs appear well within the stated Specs.
The module works fine for a time. Eventually (1 - 3 Hours), it shuts itself down.
The shut-down appears controlled. If I remove the source supply and reattach, the module starts to function again.
When I first remove the source supply, I briefly get the output back on and working. Lasts maybe 1/2 second, before running out the Caps, presumably.
I've worked the issue to the module itself - My rectification, fuse, and other safety circuitry is not the problem.
Testing has been done with more than 1 module.
My last tests were powering a standalone module from a stable 40VDC, to simulate the expected peak from the transformer, while attaching a dummy load to draw a steady 130mA.
This has eliminated the problem as being from my circuit.
I have finger checked the temperature on the module while its running. After at least 30 min, there is no significant heat. THe LM2596HVS itself is only slightly warm. I believe this was a stable temperature, as I checked many times and it always felt the same.
Any assistance would be appreciated.
I'm open to using some other sort of voltage dropping method.
As the current need is quite low, I thought maybe to try to use a Zener or voltage divider, but haven't done the math yet, as I'm still hoping to make this module work.
PS - My circuitry works fine continuously using USB power. I didn't have any issues until I tried to attach to the actual supply.