A while ago I showed this power supply kit, which I ordered from ebay. It was being advertised as an LM317 0-15V 0-5A adjustable power supply kit and it looked promising. Upon receiving the kit and taking a closer look theres 2 thing to mention, one the power supply is not based on the LM317 but on the TL431, they used TL431s instead of op-amps in this power supply design and two there isn’t much documentation about this power supply.
The components used are low quality but that is to be expected from these cheap kits coming from china so no surprises there. If you would like to use some better quality parts I would suggest replacing the electrolytic’s and the TL431s with ones sourced from known sources. Also a nice upgrade would be to use some 10 turn pots instead of the supplied ones to get some finer adjustment. But I just used the originally supplied parts to see what kind of results we get with those.
Get the TL431 power supply from these links:
Here is a screenshot with the signal measured right on the bulk filtering capacitor (4700uF). Looks like this might be the cause of the 100Hz oscillation we we’re seeing on the output.
Here is a screenshot with the current overshoot. The power supply was set for CC 50mA and I suddenly shorted the output through a 1ohm resistor. The scope probe was placed across the resistor leads on the low side ( 1mV = 1mA ). As we can see we have a huge spike of current that could potentially fry an LED connected on this power supply. However the spike lasts less than 1mS which is good and I have observed similar behavior on my HP E3611A analog bench power supply.
Here is also a screenshot with the power supply regulating the current at 50mA in CC mode. This doesn’t look right at all.
