🚀 go-pugleaf

In article <C1AH65.KGp@acsu.buffalo.edu>, v064mcqs@ubvmsb.cc.buffalo.edu (NEIL GANDLER) writes:
> 
>     Im designing a small power supply. I would like to know if using a 12v
> center tap transformer when full wave rectified and smoothed be more than
> 15 volts to allow a 12 volt regulator 7812 work properly. From my understanding
> the 78 series regulators need a 3 volt difference atleast. 
> 
> 		Neil Gandler

Yes you do need about that margin for the 7812 to reg properly.  
Depending upon 1) the amount of current you plan to draw, and 2)
the size of your (cap input) filter capacitor (the larger the better),
you may be O.K.  Also, depending upon the source of the Xfmr, just
because it's labeled 12 v does not necessarily mean it will produce
12.0 v rms with no load, often they produce slightly more.  The filter,
under no-load will charge to about 1.4 times the rms value minus the
diode drop, which for a silicon bridge will be about 1.3 v.
With modest loads, you can expect about 1.2 times the rms value and be
safe.  The internal resistance of the secondary can also enter into
it at high current values.

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