Quick ways to sanity-check a switching PSU

[Alan]

You’ve got a bench supply that seems solid on paper, but you’re not quite ready to trust it. Before you put your valuable boards at risk, it’s a good idea to put it through its paces. How do you go about checking for sag, ripple, and stability in your switching supplies?

 

[TheOhmBreaker]

First, I hook up a dummy load and keep an eye on the voltage reading. Then, I check for ripple using the scope. If everything looks steady under load, I feel pretty confident about it.

 

[groundedguru]

My initial move is to load it up, push it a bit, and scope the output.
If the signal doesn’t dip, spike, or resemble a heartbeat monitor, then it’s fit for my bench.

 

[Ohmwardbound]

I really put it to the test with resistors, monitoring any sag on the meter, and zooming in with the scope to check for ripple. If it handles that well, it gets the green light to power my important gear.

 

[barfle]

Looking back, I see that this is about switching supplies. Thevariac would probably make things act up until it hit about 80Vac input. But…

When I built my bench supply, I was trying a few new ideas, so although I was pretty sure it would work, it was a new design.

I powered it up, no load, with a variac, watching the output voltage increase until it reached my regulator setting, then continuing until I got to 120V on the variac. Then I increased the load until I hit my current limit setting.

It all worked, and it’s still my low-voltage (24 max) go-to on the bench, 40 years on. One of my better projects!