We’ve all seen those cheap bench power supply units (PSUs) for sale online, promising specifications that would cost at least a hundred dollars or more if it were a name brand model. Just how much of a compromise are these (usually rebranded) PSUs, and should you trust them with your electronics? Recently [Denki Otaku] purchased a cheap unit off Amazon Japan for a closer look, and found it to be rather lacking.
Major compromises include the lack of an output power switch, no way to check the set current limit without shorting the output, very slow drop in output voltage while adjusting due to the lack of a discharge circuit, and other usability concerns. That’s when the electrical performance of the PSU got tested.
Right off the bat a major issue in this cheap switching mode PSU is clear, as it has 200 mV peak-to-peak noise on its output, meaning very little output filtering. The maximum power output rating was also far too optimistic, with a large voltage drop observed. Despite this, it generally worked well, and the internals – with a big aluminium plate as heatsink – look pretty clean with an interesting architecture.
The general advice is to get a bench PSU that has features like an output power button and an easy way to set the voltage and current limits. Also do not connect it to anything that cares about noise and ripple unless you know that it produces clean, filtered output voltages.
I’m kinda surprised we haven’t seen a USB-C PD plus some control and display logic, sold as a “variable bench power supply” in one of these housings yet. Seems like, for lower voltage and current, they’d be trivial to make. Guess I’ll put that one on my build list.
but we have: https://hackaday.io/project/194295-pocketpd-usb-c-portable-bench-power-supply
We have, there are builds. I’ve also been eyeing the toolkitrc p200, which is not exactly the same, but a cool device anyway
I have a multi-USB charger with both USB-PD and QC3.0 that I use when I just need to power a device with a barrel jack, or when the main bench power supply is already in use. Though for the USB power supply, I only have fixed value trigger cables for it, nothing to take advantage of PD3.0.
My bench is getting a makeover soon, and I’m thinking that I might do something with a spare ATX power supply. There have are times I really could have used multiple voltages, despite lacking in current limiting or even metering. I have a 1980s/90s Motorola adjustable supply when I need that, but it’s single output.
I’ve watched too many DiodeGoneWild videos, I don’t really trust anything cheap that uses mains power.
Sometimes I use a second hand Amazon switching power supply. Other times I use the one built in to my Chinese rework station.
When I work on something old that I think won’t be happy about the noise, I fire up the ancient Heathkit power supply. I hope I don’t have to fix it many more times. Germanium power transistors aren’t as plentiful as they once were.
I have never found one of them that has a third party listing.
I have a $40 (Amazon) one branded Hyelec. It has the output switch and reads the max current setting until loaded. It also seems to do the max rated current and voltage for short periods at least. Never had occasion to go longer. The voltmeter is about 3% different from my (also low dollar) meters. But, especially for the money, I’m pleased so far.