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Author Topic: Is it safe to use the L78M05 to regulate 24 VAC ?  (Read 213 times)
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I used a bridge rectifier with four 1N4007 diodes to rectify 24VAC. I want to use the L78M05 regulator along with some capacitors before and after the regulator to get a 5VDC out. Is it safe to use the regulator for such an application? (in its datasheet it states clearly that the absolute maximum rating for its DC input voltage is 35 volts)
24 VAC RMS = 34 VAC peak to peak (24/0.707 = 33.9)
34 - 1.4V (forward voltage drop of the diodes) = 32.6V
32.6V is very close to 35V
in addition a non fully loaded transformer rated for 24VAC tends to have a higher voltage.

Thank you very much people
Regards
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I would say your pushing the limits,

for every 100 mA, your regulator has to dissipate about 3 watts,
     if your not using 100 ma, then , the diodes are unlikely to drop a full 0.7 volts, so your even more over the limit.

try using a DCDC converter off the good old ebay
   a few dollars,

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