[sdiy] Transformer question

[Simon Brouwer]

Hi Paul,

Paul Perry schreef:
> I'm sure the 15AC would be fine.
> 15v AC gives peak 22v rectified, plenty of room for the rectifier
> diode drops & the regulator headroom.

It would, with an ideal transformer. But practical transformers in a PSU
behave quite differently than one might expect.

A useful rule of thumb for regulated power supply with LM78xx and similar:
take secondary voltage 3 volts higher than the desired output voltage.
2x18V is exactly right for a regulated 2x15V PSU.

-- 
Vriendelijke groet,

Simon Brouwer
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