On Mon, 21 Apr 2008 23:45:48 +0100, Eeyore wrote:
> mick wrote:
>
>> +/- is from a 6.3v winding, bridge rectified & with a reservoir cap. It
>> should be about 7.8v in theory.
>
> Care to run your calculations for that 7.8V past us ?
>
Vac * SQRT2 - 2*Vfwd
I used the (approximate) formula:
6.3 * 1.4 - 2*0.5 = 7.82V
which allows 0.5v Vfwd for each rectifier diode. (Assuming a bridge rec
into a reservoir capacitor). I know this is often assumed to be 0.6V
each, but many rectifiers will be below this - particularly the larger
ones. You could use schottky diodes to keep it as low as poss, but I
doubt if you need anything more than a standard 5 or 6A bridge rec.
You also get a little more voltage as SQRT2 is 1.414, but who am I to
argue? ;-)
You only get 0.62 *Iac as Idc so watch the secondary current rating...
--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info
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