Is powere from a PSU fine to use with most MCU's - Page 1
Forum section: electronics / beginners

author: samarth
author_rank: Contributor
timestamp: October 17, 2021, 12:47:38 pm
content: I have an old PSU lying around gathering dust. I thought about using it as a cheap bench power supply.Is it safe for me (and by extension my mcu (an atmega 328) to use that power?Anything I should be worried about?Regards,SR`

author: wraper
author_rank: Unknown
timestamp: October 17, 2021, 01:03:20 pm
content: What PSU, ATX from a PC? If yes, it would be fine if you use standby 5V rail. The main PSU in them do not like to operate without substantial load applied though.

author: samarth
author_rank: Contributor
timestamp: October 17, 2021, 01:12:10 pm
content: Quote from: wraper on October 17, 2021, 01:03:20 pmYes, an old two star (i think?) 400-something watt PSU, circa early 2010's i think.Quote from: wraper on October 17, 2021, 01:03:20 pmI have been shorting the power line to ground (just soldered it and heat shrink-wrapped it). A post I read somewhere (not sure where, been a long time), suggested that that would work fine.If you have any better ideas, please let me know. I understand that it can get dangerous(?), and am probably wasting electricity...Regards,SR

author: wraper
author_rank: Unknown
timestamp: October 17, 2021, 01:29:46 pm
content: If there is no significant load attached to both 5V and 12V rails, there may be disbalance in voltages. Say 5V rail outputs 4.5V and 12V rail outputs 13V. Also many of them just shut down almost immediately if there is no load. Not to say the main power rails can output a very high current, so you experience a significant danger of things burning or blowing up is something goes wrong.

author: samarth
author_rank: Contributor
timestamp: October 17, 2021, 01:36:26 pm
content: Oh dear.Would I be wiser in coughing up for a power rail then?SR

author: perieanuo
author_rank: Frequent Contributor
timestamp: October 18, 2021, 07:57:45 am
content: yes, it's fine, with one observation: if it starts without load on 5V rail, that's ok (just ground the green wire if i'm not mistaken, the fourth one from that big mobo connector)https://www.overclockersclub.com/guides/atx_psu_startup/second observation: it's overkill to power 200mA load with 20A power supplysmps are ok for microcontrollers if they are correctly designed, (almost) all current devices are powered from smps, so the need to use analog supply is a myth, except sensitive applications you'll maybe never see on your desk

author: DavidAlfa
author_rank: Super Contributor
timestamp: October 18, 2021, 01:09:32 pm
content: They already have internal loads (resistors) to help balancing the outputs. I've never seen any shutting down without load.Just send the green wire to gnd (black) to turn it on.In any case, they have voltage supervisors that will turn It off if any voltage goes out of control.For very low power, 1A or so, you can use the standby 5V (purple), it's always enabled, no need to turn on the power stage.

author: wraper
author_rank: Unknown
timestamp: October 18, 2021, 02:42:54 pm
content: Quote from: DavidAlfa on October 18, 2021, 01:09:32 pmThy often have resistors but they do not provide a load high enough that PSU works well.

author: rstofer
author_rank: Super Contributor
timestamp: October 18, 2021, 04:00:45 pm
content: It may not be a good solution for import but something like this can work pretty well.https://www.sparkfun.com/products/12867

author: ledtester
author_rank: Super Contributor
timestamp: October 18, 2021, 06:04:30 pm
content: Quote from: perieanuo on October 18, 2021, 07:57:45 amExactly.You can power a MCU with batteries. When high power is needed usually you can split the circuit into a low power control circuit and the higher power part.Example: an MCU can control a string of LED lights via a transistor. The MCU can be powered by batteries and the LEDs via a high wattage power supply. You can do a lot of testing and debugging of the MCU without hooking it up to the LEDs.Another reason not to use such a powerful supply is that if something goes wrong it can deliver 20A into your circuit. Find a supply which is appropriately sized for your application.

author: perieanuo
author_rank: Frequent Contributor
timestamp: October 19, 2021, 06:47:43 am
content: Quote from: DavidAlfa on October 18, 2021, 01:09:32 pmi repaired hundreds, there are models i was forced to put some light bulb to start them. if you haven't see one it doesn't mean they doesn't exist

author: David Hess
author_rank: Super Contributor
timestamp: October 19, 2021, 04:18:28 pm
content: I would check the output regulation with an oscilloscope with little or no load, and add a minimum load on the 5 and 12 volt outputs as appropriate.