Electronics > Beginners
Transformer voltage for dual power supply (+12V / -12v)
belzrebuth:
Hi all,
I've got a 2 x 12VAC toroid transformer and was wondering if the 12VAC will be enough for a symmetric 12V power supply.
I've already got the pcb for the dual power supply and it requires LM317/LM337 regulators so I can't use low dropout regulators (except maybe if the pinout is the same).
Can I use this transformer to make a dual 12V power supply?
ocset:
Yes 12vac is 17vpk.
subtract 2v for the diode bridge.....down to 15v.....subtract a bit for winding voltage drop.....your down to 12V...so you should be ok as long as your winding voltage drop is not too much.
belzrebuth:
Thanks!I'll try it then.
Here's the power supply I'm talking about..
http://musicfromouterspace.com/analogsynth_new/POWERSUPPLY2009/POWERSUPPLY2009.php
It states that'll work with a 2x12 transformer for 12 volt output.
I'm a bit skeptical about the 10,000uF capacitors though..
I find their value a bit too much for the power supply's amperage rating..
I want the lowest ripple possible but still..
I thought that 4x4700uF at 25V would do the job nicely..
I think there was a formula for calculating the required capacitance for the max current draw..
Zero999:
I'd say it's marginal, especially for any sizeable current draw. Use Schottky diodes to reduce the voltage drop and you stand more of a chance, even with the LM317 and LM337.
drussell:
--- Quote from: belzrebuth on August 25, 2018, 05:14:10 pm ---Hi all,
I've got a 2 x 12VAC toroid transformer and was wondering if the 12VAC will be enough for a symmetric 12V power supply.
I've already got the pcb for the dual power supply and it requires LM317/LM337 regulators so I can't use low dropout regulators (except maybe if the pinout is the same).
Can I use this transformer to make a dual 12V power supply?
--- End quote ---
\$12.0 * {\sqrt{2}} = 16.97\$
(As others have stated while I was trying to discover how to post with MathJax... :) )
You'll really need to check the actual voltage. If it is slightly higher than 12 at load, you'll probably be fine. The old 12.6v filament transformers were usually just enough to get actual 12 volt DC regulated at full load with a 7812, etc. non-LDO regulator. YMMV.
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