Electronics > Beginners
Transformer voltage for dual power supply (+12V / -12v)
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Ian.M:
Yes, as I thought, the best option is to move the bridge or discrete diodes off-board.   Just link the outer pins of the bridge footprint, each to the nearest middle pin and Sec1 becomes bridge +, and Sec2 becomes bridge -

Using individual Schottkys isn't too horrible if they are isolated tab packages - just bolt them down with a dab of heatsink compound, and wire them up to a nearby tagstrip.  Its probably worth putting Kapton tape on the chassis under the diode legs so they cant short to the chassis if they ever get bent down.
belzrebuth:
Could you recommend a particular schottky package that would fit my needs?

I've never used those so I'm a bit clueless on what to get.
I've only seen them on SMPS power supplies I think..
Audioguru:
I haven't looked at the waveform of my mains electricity for many years. I betcha it has its peaks squashed by all the full wave rectifiers and filter capacitors in nearly everything I have turned on most of the time. Then the formula about the peaks are 1.414 times the RMS voltage goes out the window and your LM317 powered from a 12V transformer and rectification will have poor voltage regulation.
Does your mains electricity have a voltage drop each time the refrigerator or air conditioner turns on? Mine doesn't because the transformer feeding mine and a few other homes is next door.
Audioguru:

--- Quote from: belzrebuth on August 26, 2018, 10:34:12 am ---Most bridge rectifier packages state Vf of about 1V.
--- End quote ---

For each diode. A bridge rectifier has two diodes in series so the voltage drop is 2V.
belzrebuth:
I've just discovered that I also have two identical toroids (also 12V).
These output 13.8V unloaded.

They're 50VA each so I could maybe try those two for a 2x12V substitute.
I think I have other transformers laying around too but they're not toroids..

I really need to get the psu board populated in order to perform some hands-on tests (I could monitor the voltage while turning the air conditioner on for example).
Getting a new transformer is not that expensive but I wouldn't mind trying if what I've already have works..
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