Running Regulators in Parallel... - Electronic Circuits Projects Diagrams Free

ronnyelectron · 21st October 2009, 12:35 AM

Hi, I'm Ron, just a hobbyist.

My question is:

Is it possible to run more than one voltage regulator off of one power transformer secondary?

Example.....24vac/1A secondary full wave bridge rectified.... can this DC go to a 7805 for a 5v circuit and a 7812 for 12v?

Thanks!
Ron

Boncuk · 21st October 2009, 02:30 AM

You can do this, but consider that the LM7805 has to dissipate a lot of power. (It has to kill 19V!)

If the current draw of the 12V regulator + the current draw of the 5V regulator is below 1A you might reduce the LM7805 power dissipation by connecting both regulators in series.

That way the LM7805 just has to kill 7V.

Plan for a heatsink of both regulators.

Boncuk

Sceadwian · 21st October 2009, 02:32 AM

Yes. But you're limited to 1amp total current draw.
That's wasting a HUGE amount of power though, almost 2/3rds of your entire power simply as heat. Bad circuit design, SMPS or a different set up would make much more sense.

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21st October 2009, 12:35 AM	#1
ronnyelectron	Running Regulators in Parallel... Hi, I'm Ron, just a hobbyist. My question is: Is it possible to run more than one voltage regulator off of one power transformer secondary? Example.....24vac/1A secondary full wave bridge rectified.... can this DC go to a 7805 for a 5v circuit and a 7812 for 12v? Thanks! Ron

21st October 2009, 02:30 AM	#2
Boncuk	You can do this, but consider that the LM7805 has to dissipate a lot of power. (It has to kill 19V!) If the current draw of the 12V regulator + the current draw of the 5V regulator is below 1A you might reduce the LM7805 power dissipation by connecting both regulators in series. That way the LM7805 just has to kill 7V. Plan for a heatsink of both regulators. Boncuk __________________ Proper Planning Prevents Piss Poor Performance

21st October 2009, 02:32 AM	#3
Sceadwian	Yes. But you're limited to 1amp total current draw. That's wasting a HUGE amount of power though, almost 2/3rds of your entire power simply as heat. Bad circuit design, SMPS or a different set up would make much more sense. __________________ "Because I be what I be. I would tell you what you want to know if I could, mum, but I be a cat, and no cat anywhere ever gave anyone a straight answer, har har."