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How to create dc input to dc 5v and 12v (two outputs) circuit? Answered

I need to create a circuit with two different output voltages but with a single input voltage. The output voltage must be 5v and 12v dc. The input voltage must be max 12v dc (for using 12v dc power adapter from ac mains).



Best Answer 3 years ago

Here you are


This was what I wanted, but there's something more. I want 750mA current on the 12v output and 1A-2A current on the 5v output. I assume the 5v output has about 1A current because of 7805, but what about the 12v one?

You can use the above circuit along with the LM317 connected as a current regulator.

Screen Shot 2014-11-20 at 7.41.53 pm.pngScreen Shot 2014-11-20 at 7.42.00 pm.png

If you are absolutely sure the input will never rise above 12.1vdc then get a 5Watt 12.2Volt zener and a 1/2 ohm 5w resistor.

There are 2A 5V regulators you can search for, but make sure you use a hefty heat sink to cool the 5v regulator.


3 years ago


which Zener and R1 resistor are proper on the Circuit ?

I cannot find any data of R1, Zener.


Good grief. With all due respect to the respondants, design and build something. Afaik, this is instructables, not a Chinese goods outlet store. What exactly does one learn by purchasing everything premade? (clue: absolutely Nothing good) It's in part what got America into the mess the rest of the world (and sadly, many who claim they're american) wanted us in in the first place. Dependant and incompetent.

Your point is strong

Kids are solder lazy

Slapping China bits together for a song

And software they are not able lately !

lol Second that ! there are some times you need a breakout board, and others you need some proto-board.

I would encourage you to stick with the LM-7805 (for 5V, less then 1A. All at about $1.50) As-per 12v, the adapter should provide the voltage you need. **Be cautious, a Switching Power Supply (Like most wall warts) will jump much higher then it's rated voltage for just a moment. After it stabilizes, you will get a constant voltage. Some electronics will tolerate this, many wont. I have ran many **12v** devices off a switching wall wart, with minimal issues. May I ask what device you are running off the 12v rail? It could help determine how best to tackle it.

And Iceng, I see what I believe is a Zeener Diode, may I ask what it is for? Is it there for stability, a rectifier or just for protection?

MMmmmotor power aside, it look nice, zeners are really very fast, and I do not believe authors 12v peak only. So it is a loose protection regulator loosing only o.375v...........

"MMmmmotor power" I will look at after I get over this cold :P but does the zeener help reduce the initial voltage spike in a switching power supply? I've been looking for a nice solution for this problem aside from a delay(X) + a Transisrot, or a Linier Regulator. akki5230 up there might apriciate the help :)

Yes it does, but for real surge protection try a TVS diode.

They have a large area PN junction which is a bit slower then a zener.

But a TVS diode can absorb 400 to 2500 watts.


I totally agree with you, I am not a guy who likes to use "ready-made" material/circuits. I really love to design my own and improving skills/knowledge... That's why I posted a question or I would have already bought from ebay...

Power two separate voltage regulators from the source, then deliver their out to two (or more) outputs.

I would have done this but I'm not sure what current would they provide because I need 750mA on 12v and 1 or 2A on the 5v output.

The 5V can be accomplished using the 7805 in a ?TO-3? (the big package) or buy suing one of those high output variant 3-terminal swithcing regulators.

the 2A load could be problematic for simply using a 78-series and will require a two stage regulator design (78-series followed by a bulk load transistor)

Afaik, the 78-series datasheets from National, etc have design ideas that include a boosted output design for extended loading, or at least they used to. If they're not embedded, then National et al have probably moved the design ideas to another doc.

Not saying a lazy, "buy" solution isn't efficacious, just well, you knwo. I said it already.

good luck

+1 to buy

Circuitry not willing

As easy as a sigh

And free shipping !

I bought one of those for controlling the voltage going from a computer power supply to some LED's that were originally set up to run on batteries.

Then I recently discovered something even better.


You can get the lights alone or you can get the power adapter with them. I got a set and was really amazed. The power adapter takes a DC input of up to 24 volts and regulates it to what the lights need. It comes with a remote that is RF and it can crank the voltage down so the lights are barely on. Not to mention also on /off functions and different modes including fades and strobe effects. It adds $2.00 to the cost of the lights so that makes it a 2 dollar unit.