Ok, so I dont know where else this would go other then here. And since I know that the majority of you know what in the hell you're talking about when it comes to schematics and electrical work, I come here now for your help.

I have a schematic for a variable output DC power supply, it fits my needs perfectly, however it is missing a few things that I would like to add to it, I just dont know where to add them... The schematic is this:

I am wanting to add a momentary switch to complete the circuit the circuit and turn the voltage on, on top of having the "on/off" switch. Im wanting to have a 1/4" jack to plug the momentary switch into.

I would also like to add a 12V fan to the circuit that comes on when the main power switch is turned on to help cool the circuit down.

Then I would also like to 1/4" jacks to output the current to.

If this seems a bit stupid or whatever, I really do apologize but I am wanting to try to build a power supply and I am at a bit of a loss at adding the things I would like it to have, so any help you guys can give me would be greatly appreciated.
Why do you want a killswitch? (This is essentially what a momentary power interruptor amounts to).

You won't need a fan. Heatsinking the voltage regulator is good enough.

You'd be better off using BOSS style barrel plugs. Afaik, there is no such thing as a pedal (or anything else) that gets power from a 1/4" jack.
Its not a pedal, its a 120V power supply. (I just didnt know where else to put this since it regards building something). I know the heat sink should be good enough for keeping the voltage regulator cool, but I want to be even more secure in it by adding the fan. The "kill switch" is for a foot pedal. Its basically going to be a tattoo power supply, so I want a momentary switch jack for plugging in a footswitch.
I'll draw you up a diagram in a second..

a quick look doesnt tell me what voltage that's providing at the output (variable based on that 5k pot there?), so I won't show you where to get 12v for the fan in the diagram, but...after taking a harder look it shouldnt be unbelievably hard to figure out..
Yeah its a variable output circuit... With the stock schematic its supposed to be between 1.5-35V.
To be honest I wouldn't go through the trouble of building a circuit for a 12VDC power supply for the fan. A heatsink should be fine.
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hope it makes sense to you...

like I said, idk off the top of my head where you'd get 12v to power the fan, but you could have a seperate supply to it ...maybe just get a 10:1 power transformer, 4 diodes for another full wave rectifier, and a couple of filtering caps..

..anyway, I just drew in a little tab that says '+12v', so ..you can get your fan's power from wherever, really.. but like jim said, you probably wont need it, anyway..

i'm tired, so sorry if anythings unclear.. just ask
Im not sure that it is worth building a variable PSU is worthwhile. My personal preference would be to connect a 12 volt transformer (not a wall wart, a raw transformer) into a full wave rectifier and smooth at with some capacitors. At this point, without doing any calculations, I guess the voltage will be 15VDC. Then use a 7812 or 7809 regulator to get 12v/9v out.

Whichever circuit you build, avoid using fans. They will add noise onto the power supply as well as making audible noise. You should be fine with just a heatsink of the appropriate size on the lm317 or 78xx regulator. A fan should be a last resort.
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^he's already said that the main power output of this thing is for a tattoo machine of some sort, so noise doesn't really seem like much of a problem..
but yeah, the way I suggested to get 12v to the fan is the same as what you said.. (transformer, full wave recto, filter caps)

TS, you don't really need a fan, like most people have said. if you still think you'll need one, going the transformer route would probably be your best bet, I'd say..
You already have a on/off switch.

Swap the values of C1/C4. The pre regulator filtering should be bigger than the most. I would use 470mF, 100mF personally.

If your really worried about heat (you really shouldn't be) you can heatsink the regulator to the enclosure. Just make sure you use a mica insulator and double check the regulator is not connected to the enclosure in any way.

Edit: James there are a few errors in your diagram, might want to double check it.
Last edited by kurtlives91 at Aug 12, 2009,
Damn... I knew I could count on you guys for help. I appreciate all the replies all ready...

The circuit in the schematic above comes in a kit. I was looking at it because the kit was only like $16 and it has all the components, pcb, and it does have a pretty big heat sink. But it said in the description and on the pdf file that was with it that it was a transformerless option to a variable output power supply. However, I have taken apart my current power supply to have a look at it and see how it works and it does use a transformer.

Im pretty sure that a transformer keeps things better regulated then a circuit without a transformer, so Im a little skiddish now about what circuit to go with for the main power supply circuit because I dont want to screw up my tattoo machines because they are pretty expensive. But the only reason I would like to try making my own power supply is because the high end ones (which mine isnt) are anywhere from $299+ and I really dont want to spend that much on something that I could possibly make myself. All of the high end models have a voltage meter built in, 10 turn pot, fans (because the power supplies themselves can become hot after long sessions), the footswitch jack, and 1 or 2 output jacks that are switchable from one to the other. I would like to incorporate all of those things if possible, I just dont really know how to blueprint the schematic to make it all work.
Quote by music_mike
Its not a pedal, its a 120V power supply.

This is NOT a 120v power supply. Do not connect this to the mains !

So Im not too sure what your trying to do, but an LM317/338 will not replace a transformer.

You cant use audio jacks for power. It will short when inserted.

There a reason why something costs $300, probably high current. But some supplys are so cheap now, you could get something better for $10.

So what voltage and current do you need? and I assume its mains input from what you have said so far.
Last edited by Kramdra at Aug 12, 2009,
Quote by Kramdra
This is NOT a 120v power supply. Do not connect this to the mains !

So Im not too sure what your trying to do, but an LM317/338 will not replace a transformer.

Yes I know. What I meant by everything I have typed is that the circuit is for a 120V wall charge to be converted down to a variable voltage output (between 1.5 and 33) at about 5 amps. The circuit comes in a kit form from a respectable dealer so Im sure that it has been blueprinted and tested to make sure that it does what it says it will.
You cant use audio jacks for power. It will short when inserted.

I never said that I wanted to use audio jacks for power. The power will come from a wall outlet. The audio jacks are for use of "plugging in" a momentary style footswitch and another audio jack to be the output for a tattoo machine clipcord. The audio jacks would just serve as a means of completing the circuit and outputing the power.
There a reason why something costs $300, probably high current. But some supplys are so cheap now, you could get something better for $10.

They arent expensive because they are high current. In fact the current is fairly mild. They are so expensive because they are an "industry specific" piece of equipment which means they can charge more for them. Parts to build them arent really that expensive, but since they are made specifically for a small demographic of people they tend to be astronomical in price.
So what voltage and current do you need? and I assume its mains input from what you have said so far.

The voltage has to be variable on the output, between 1.5/3 to 18/20. In tattooing you dont really use voltages less then 3 or more then 18 but a little cushion never hurts. The amperage can be anywhere from 2 to 5 amps. Usually 2 amps is perfectly fine for what we do.

So hopefully that helps answer what ever I was unclear on. It was late last night and I was kind of rushing through it when I typed.
This is not electrical advice, but advice nonetheless.
If you will be using this tattoo machine on people, especially as a business, then you should think hard before building your own equipment. If your homemade power supply fails and a customer were to be injured and sue you, you will bear all responsibility. If a commercial (industry spec) unit fails on you, you have much more legal protection. Just something to think about.
Last edited by cedricsmods at Aug 12, 2009,
ok I understand better what your trying to do - and a linear chip like that just wont work. If you need a 3-20v range at that current, it will make too much heat.

Look for a switching regulator they are extremely cheap, but maybe not for an adjustable one, just becuase they are not very commonly needed.

Or you could use a voltage follower - linear but cheap, or PWM like switching but doesn't work with all things

And when I said about audio jacks, I meant for any power, becuase the contact in the socket will bridge the insulator on the plug and short out your DC supply. This is not a problem for audio.
Last edited by Kramdra at Aug 12, 2009,