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Power supply duel_5v/15v from 230:15v 1amp transformer

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sajsaj220

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Along with subject and ckt attached,
why getting 19.5v(more than tranformer sec rating) insted of 15v.

The measurement of volt as follows with digital meter:
The tr sec o/p-> 15.96v,
o/p-1 ->>5.2v
o/p-2 ->>19.5v


tnx Power supp_5v_15v.JPG

Can u explain the fact behind it and do i get ~15v.
 

if the 230V is a little high, you'll get a little more on the 15 V side

15V RMS is 21.2 V peak
one diode drop through the bridge, a second diode drop through D1,
and a third diode drop on the return through the bridge yields 21.2 V - 3(0.7 V) = 19.1V

you need to put a load across C5 to see anything besides the peak voltage
diode D1 and capacitor C5 act as a peak detector, so you are seing the peak voltage

how much current should the 15 V supply provide?
connect R = 15V / (expected current in amps) across C5

you might want a three terminal regulator after C5 to provide regulated 15V
as you did for the 5V supply
 

Hi,

Most transformer and power supply ratings are at full power load .... not without load.

Klaus
 

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