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Need a little help on circuit for 120VAC to 12VDC

irishluck

Mar 12, 2014
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Hi guys,

I just need a little help here.

I need to find a schematic for a circuit on 120VAC to 12VDC converter
I don't need a lot of amps. I think at most would be 5A. But I just need to get a schematic with the proper parts
to build this.

Any help would be great!
 

Minder

Apr 24, 2015
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Do you need regulation?
1 -120v - 9v secondary 70va transformer.
1- 10 amp bridge rect.
1- 1000μf capacitor.
1- 7812 (if regulation needed).
M.
 

irishluck

Mar 12, 2014
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What do you mean by regulation?

I'm still learning a lot about electronics right now. I'm in school here at PCI in kcmo to get my associates in electronics technology.
Unfortunately we haven't gotten to a lot of stuff yet.
Just started our AC portion of school. Alot to learn!

The circuit just needs to be basic using a 120vac that needs to put out 12vdc.
It will be on for about 10 hours a day if that means anything?
 

Minder

Apr 24, 2015
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The components I listed will output ~12VDC but not regulated without a electronic regulator IC such as the 7812 mentioned, without it the 12v could fluctuate slightly with load and AC source voltage drop, it all depends what you are using the 12v for and type of device.
Example DC motor, lamps or LED's do not need regulation.
M.
 

BobK

Jan 5, 2010
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The components I listed will output ~12VDC but not regulated without a electronic regulator IC such as the 7812 mentioned, without it the 12v could fluctuate slightly with load and AC source voltage drop, it all depends what you are using the 12v for and type of device.
Example DC motor, lamps or LED's do not need regulation.
M.
Only if you can handle 12V peak with 12V ripple!

1000uF is way too small for 5A output. Try 22000uF to get about 1V ripple. And use a 12V transformer and a regulator.
Bob
 

Minder

Apr 24, 2015
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. And use a 12V transformer and a regulator.
Bob
Regulator still only needed depending on 12v device driven!
Also if unregulated 12vac secondary will give approx. 16vdc
M.
 

BobK

Jan 5, 2010
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Only with no current drawn. I simulated it with a 9V AC source. With a 1000uF cap it peaks at 11.4V and goes all the way down to 0. You are not going to get 12V 5A from a 9V transformer. The peak voltage is 12.76 and the 2 diodes in the bridge will drop about 2V at 5A.



Bob
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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Another point, @irishluck -- if you're new to electronics, perhaps you should consider the safety aspects of a circuit which connects to the mains.

If you can grab an old PC power supply, you will find you have an instant 12V power supply (along with other voltages) which may be capable of 25A or more,
 

ver chan

Jun 27, 2015
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dont forget to use fuse to provide protection for your project, and if it will run for almost 10 hours a day, put an exhaust fan to drives out excess heat. try to visit e-gizmo.com to view some schematic or engineersgarage.com
 

Arouse1973

Adam
Dec 18, 2013
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I beg to differ, I have used the 78H12A up to 5a, no problem.
There are a few examples out there also.
M.

Ok M yes that one will allow 5 Amps. But you said originally 7812, most people regard this as a 1.5 Amp device.
Thanks
Adam
 

BobK

Jan 5, 2010
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Beginners are well advised to purchase a COTS (Commercial Off-The-Shelf) bench power supply with voltage and current controls and meters for both. The last thing you need when learning electronics is an unreliable power supply for your experiments. If you want to do any analog work, purchase a ±15 V DC bench supply too.
I disagree with this. When I was first starting out, building power supplies was a good exercise for me and produced something actually useful. I still have a 5V 7805 power supply and a ±12V power supply made from zeners as pass transistors that still work 40 years later.

Bob
 

hevans1944

Hop - AC8NS
Jun 21, 2012
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I disagree with this. When I was first starting out, building power supplies was a good exercise for me and produced something actually useful. I still have a 5V 7805 power supply and a ±12V power supply made from zeners as pass transistors that still work 40 years later. ...
When I started out, about 1950 or so, I had to beg money from my mom or my grandmother for dry cell batteries to do simple electrical experiments. There was little opportunity for a six year old child to earn money by working. But I soon "graduated" to building power supplies from salvaged transformers and selenium rectifier stacks. It was ten years later before I could afford the new-fangled silicon diodes and silicon controlled rectifiers. Still later, while in my late teens, I built a variable voltage-regulated vacuum tube power supply, still using salvaged parts (mostly from TVs by then), for my first amateur radio transmitter as well as for bench use. That was the last time I did any serious work with vacuum tube electronics design for almost another twenty years. There were many power supply projects in between.

Did I learn anything from constructing power supplies? You bet I did. I also learned that if I could afford to purchase one, I could get on with my electronics hobby much easier and quicker! Hence my recommendation to beginners: there will be plenty of opportunities to build power supplies, and you definitely need to learn how to do that, but if you want to learn electronics you need a reliable, stable, power supply right now. Purchase a good one now and you will use it forever. Learn later how to build custom power supplies for your projects. Well, maybe not too much later... sooner is better, but get the basics down pat first. Ohm's Law, Kirchoff's Laws, calculating DC voltages and currents in arbitrary series and parallel circuit will all help you design robust power supplies.

That's just my opinion, and I can't argue that @BobK has a valid opinion that is the exact opposite. After all, we both took the same route when starting out but have arrived with different opinions. As always, your mileage (or kilometers) may differ. Just remember the whole point is to have fun. Without the fun part you may end up just having a job.

Hop
 

davenn

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Sep 5, 2009
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I beg to differ, I have used the 78H12A up to 5a, no problem.
There are a few examples out there also.
M.

you never mentioned 78H12 in your other post --- naughty naughty

and even if you did ... the device seems to be non existent .... cant event get a datasheet for it
its mentioned all over google but they are all dud links
 

hevans1944

Hop - AC8NS
Jun 21, 2012
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Seems this part originated in Asia, possibly Taiwan. Good luck finding a distributor. I did find a datasheet.
 

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Minder

Apr 24, 2015
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And the point of whether regulation is even needed, without detail of the nature of the actual load required to be operated??
M.
 
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