Pointers on Power Supply Design - Page 1
Forum section: electronics / beginners

author: jdutky
author_rank: Regular Contributor
timestamp: December 16, 2020, 04:11:33 am
content: I need a small power supply to provide a few tens of milliamps of current and selectable voltages of +/- 50 V, +/- 25 V, and +/- 10 V and I'm having a really hard time finding pre-built units that will do the 50 V range. My first thought was to build a simply linear supply using a center tap transformer to produce +/- 55 V from wall power, filter and rectify that, and produce the other voltages using DC/DC converters but I'm finding that I'm at the (very modest) limits of my skill and knowledge.Does anybody have any recommendations for books or web sites that would be a good introduction to power supply design, or maybe have any COTS products that might be a good fit for the +/- 50 V stage?I'm willing to build my own transformer, if I must (it would be nicer to find one ready made that I wouldn't need to worry about hooking up to wall power), and I'm willing to study whatever I need to in order to understand the subject. I've already got a basic understanding of electronics, but I feel like dealing with wall current is dangerous and likely has hidden depths.-- Jeff Dutky

author: ledtester
author_rank: Super Contributor
timestamp: December 16, 2020, 07:11:18 am
content: Here's a thread with some ideas:https://www.diyaudio.com/forums/power-supplies/5727-voltage-37-negative-regulator.htmlAs mentioned, there is a high-voltage version of the LM317 which goes to 60V -- the LM317HV and you can still get them.A high-voltage version of the LM337 is harder to find (and only goes to -47 V anyways), but the above thread refers to high-voltage design ideas starting on page 12 of this National LM317 datasheet:https://media.digikey.com/pdf/Data%20Sheets/National%20Semiconductor%20PDFs/LM317L.pdfOne example -- a "Short Circuit Protected 80V Supply" using a LM317:You probably can just invert this to get a regulated negative voltage using an LM337.

author: jdutky
author_rank: Regular Contributor
timestamp: December 16, 2020, 11:32:09 am
content: Cool, I ordered some LM317HVs and LM337s pretty easily. Sadly, that leaves me without a -50 V rail, but maybe I can do without that.Is there a reason that there are no negative voltage regulators with greater than -37 V outputs?The linked thread is a little over my head, but gives me plenty of terms to start googling on. It looks like I need to buckle down and understand how to use the LM317.Thanks.

author: rdl
author_rank: Super Contributor
timestamp: December 16, 2020, 06:26:23 pm
content: Is it not possible in this case to use two LM317HV in series? I've seen it done with regular LM317s to make a +/- 12 volt supply.

author: james_s
author_rank: Super Contributor
timestamp: December 16, 2020, 06:30:12 pm
content: If you have a transformer with two independent secondaries that should work, I mean they don't make special negative voltage batteries, you just wire two in series and call the joint between them "ground".

author: ledtester
author_rank: Super Contributor
timestamp: December 16, 2020, 09:33:44 pm
content: Quote from: rdl on December 16, 2020, 06:26:23 pmYeah - can work if the supplies are independent. In general it might not work and/or there are regulation issues:https://www.analog.com/en/analog-dialogue/studentzone/studentzone-july-2017.html#

author: ledtester
author_rank: Super Contributor
timestamp: February 07, 2021, 08:04:07 am
content: FesZ Electronics on youtube just did a video on how the high-voltage designs on pages 12 and 13 of the LM317 datasheet work including suggestions for improvements and a LTSpice simulation:DIY - High voltage linear regulator based on the LM317 - Part 1https://youtu.be/Qud914PqlqsLM317 datasheet:https://media.digikey.com/pdf/Data%20Sheets/National%20Semiconductor%20PDFs/LM317L.pdfAlso look for follow-up videos: Parts 2 and 2b.