Desktop power supply 4.0V - Page 1
Forum section: electronics / beginners

author: Mp3
author_rank: Frequent Contributor
timestamp: July 20, 2020, 08:23:01 am
content: I am looking to design a small power supply to turn a battery only device into a mains powered one,the battery is 4.15VDC at full and 3.7v when it stops working.so my goal is power it with good consistent 4.0v.It will pull around 30w generally, never more than 40wShould i get a 5v switching psu and adjust it close to 4.0 as it will go or should i use a 12v switching and use a diode+resistor?my understanding is that i could get away with better efficiency using the 12v and a resistor, but i'd be worried about pushing so much wattage through it.I don't have EE training but my gut feeling is that's not a good way to do it.

author: kjr18
author_rank: Regular Contributor
timestamp: July 20, 2020, 08:55:14 am
content: I think most of these metal boxed meanwell power supplies have some voltage regulation, not sure how much you can take it down. If you could find one like that, you could use it. Other thing you could try: get some other power supply (even laptop power supply would do), and connect it to suitable buck converter.

author: MarkF
author_rank: Super Contributor
timestamp: July 20, 2020, 09:14:55 am
content: 40W @ 4V is a big ass power requirement for a battery operated device.Were you using a car battery?That would require a 10A output. Are you sure of your requirements?The smaller the different between you input and output voltage; the less power (heat) your power supply will need to dissipate. However, you do need a few voltages for proper regulation.

author: magic
author_rank: Super Contributor
timestamp: July 20, 2020, 11:33:42 am
content: 10A is where I would expect to see synchronous rectification. This may or may not work right if you reduce output voltage to 4V, depending on the FETs they used.Not sure how you want to reduce 12V to 4V with a diode and resistor?

author: Mp3
author_rank: Frequent Contributor
timestamp: July 21, 2020, 03:35:57 am
content: Quote from: magic on July 20, 2020, 11:33:42 amNeither do i , that's why i'm asking here in Beginners forumI don't know of any buck converter which can handle a throughput of 7-10A, is that a safer method?I was thinking of those mean well supplies with the adjustable 5V, but if i go that method, i should probably just buy a LRS-350-4.2 and call it a day.As long as I can push around 30W at 4V, i will be good.

author: bdunham7
author_rank: Super Contributor
timestamp: July 21, 2020, 03:51:47 am
content: Can your device tolerate power supply noise?

author: MarkF
author_rank: Super Contributor
timestamp: July 21, 2020, 05:42:56 am
content: Quote from: Mp3 on July 21, 2020, 03:35:57 am- You can't drop 12V to 4V with a zener diode and resistor at those current levels. Well, not entirely true but I wouldn't do it here.- Just purchase the 4.2V supply you mentioned. Get a supply that is designed for your requirements. I don't know why you would consider anything else since they make them. And you will spend just as much going a different route.- It is unlikely the voltage adjustment on a 5V supply will allow that much adjustment.

author: Zero999
author_rank: Super Contributor
timestamp: July 21, 2020, 10:20:06 am
content: What device is it? Do you have the user manual/data sheet? Perhaps it might work from a standard voltage such as 4.5V?