EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: jdutky on December 16, 2020, 04:11:33 am
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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
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Here's a thread with some ideas:
https://www.diyaudio.com/forums/power-supplies/5727-voltage-37-negative-regulator.html (https://www.diyaudio.com/forums/power-supplies/5727-voltage-37-negative-regulator.html)
As 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.pdf (https://media.digikey.com/pdf/Data%20Sheets/National%20Semiconductor%20PDFs/LM317L.pdf)
One example -- a "Short Circuit Protected 80V Supply" using a LM317:
[attach=1]
You probably can just invert this to get a regulated negative voltage using an LM337.
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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.
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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.
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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".
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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.
Yeah - 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# (https://www.analog.com/en/analog-dialogue/studentzone/studentzone-july-2017.html#)
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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 1
https://youtu.be/Qud914Pqlqs
LM317 datasheet: https://media.digikey.com/pdf/Data%20Sheets/National%20Semiconductor%20PDFs/LM317L.pdf
Also look for follow-up videos: Parts 2 and 2b.