Products > Test Equipment

Cheap bench power supply?

<< < (4/10) > >>

slybunda:
any options for powering small stuff like mosfets and led's and microcontrollers for a little while on a breadboard? usb powerbank and some sort of buck/boost converter possible?

shapirus:

--- Quote from: slybunda on January 28, 2024, 09:43:05 pm ---any options for powering small stuff like mosfets and led's and microcontrollers for a little while on a breadboard? usb powerbank and some sort of buck/boost converter possible?

--- End quote ---
I got one of these ~3 years ago: https://www.aliexpress.com/item/1005005145280146.html and coupled it with an old school transformer+bridge+caps AC/DC PSU (I thought I needed this kind of galvanic isolation at the time).
It works fine.
I charged batteries with it many times, because nobody told me it was a bad idea. Just as expected, no issues whatsoever (though it does consume a little bit of current, like few mA, when it's off and you apply voltage to its terminals).
Voltage regulation is off by ~10 mV. Current regulation struggles to work correctly up to about 25-35 mA, but it glitches on the safe side: sometimes it goes into CC mode and lowers voltage when it's not yet necessary. Higher than that, it works well.

One caveat in this configuration: because of the capacitive coupling between the transformer's windings, there is considerable AC voltage between either of the terminals and mains earth or a human. Of course they are in phase, so it's proper DC between the two of them, and it's a very high impedance source, but I did kill a few MOSFETs with this voltage (connect source to one of the PSU terminals, touch gate, bingo). It would make sense to add a PE connection to optionally tie one of the terminals (negative) to mains earth to avoid these issues.

The only scenario so far when I needed anything else has been when more than one power rail was required. In these cases a proper multi-channel (2 or better 3) lab PSU would be much more convenient.




Noise at 15V output with a 1.2k resistor as load, 5us/div horizontal, 10mV/div vertical:



KungFuJosh:

--- Quote from: shapirus on January 28, 2024, 10:30:02 pm ---I got one of these ~3 years ago:

--- End quote ---

Those are great. I use one of those in my FUtracer curve tracers. I usually get this version: https://www.amazon.com/gp/product/B01LWXAC5E/

I haven't tried this one yet, but it looks interesting for people that need more voltage: https://www.amazon.com/dp/B0C89F4XJY/

shapirus:
BTW, speaking of noise, you should not necessarily rely on power being clean. If the circuit you develop requires very clean power, then adding filters is on you. If your device will be powered by e.g. a USB port, then you can expect any sort of noise in power input, and you need to filter it anyway.

If you need to test some components etc. and make precise measurements that can be affected by the PSU's switching noise, then it's easy to add filtering between the PSU and the circuit, including, if necessary, a linear regulator. I really see no point in requiring that your bench PSU should necessarily be a linear one. Switching converters, even cheap ones, should be fine for most cases.

shapirus:

--- Quote from: KungFuJosh on January 28, 2024, 10:40:20 pm ---I haven't tried this one yet, but it looks interesting for people that need more voltage: https://www.amazon.com/dp/B0C89F4XJY/

--- End quote ---
Yeah it looks quite good, and it's btw a lot cheaper (about $35) on Ali. I might build a second unit to serve as a second channel, will see. However when you add the price of an AC/DC PSU... it may well be that getting the ready made one (I am sure they make ones already with a case and AC/DC supply) will cost the same, if not less, not to mention that it's easier. Building my first one was fun, but it was just enough of that particular kind of fun for me :).

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod