Author Options:

How to supply voltage to a circuit which requirs +12v, +5v and GND Answered

I need to know how to supply voltage to a circuit which requirs +12v, +5v and GND. The circuit is a Pic Programmer. Im sorry if this is a stupid question, but im kinda new to electronics and would appreciate any help provided.

Please look at the circuit attached below. Thanx


The forums are retiring in 2021 and are now closed for new topics and comments.

9 years ago

Just use a 7812 for the 12V supply, and a 7805 regulator for the 5V supply. Very easy, the circuits are are on the datasheets. You can then use any power supply from 13 - 30 volts to power the circuit.

Jack A Lopez
Jack A Lopez

9 years ago

It looks like those pictures came from here:

And that page does contain some explanation of how this thing is supposed to work.  I just thought I'd mention that page for completeness, in case anyone is wondering where the circuit diagrams came from.

Regarding the power supply:  You want +12V, +5V, and ground. 

Coincidentally those are the same voltages used by most desktop computer hard drives. Or at least that's true at the time of this writing.

A quick and dirty way to power this pic programmer would be to just run a cable from the computer power supply, the one supplying power to the same computer that parallel port is attached to.  One way to do this is via a spare hard drive power cable, e.g. the kind that coverts the power connector for an IDE drive to a SATA drive. Hack one end of it off, and connect it to the wires going to your circuit. The red wire is +5. The yellow is +12. The two black wires are both ground.

The only reason I can think of that might be a bad idea, is if the circuit(s) attached to this programmer cannot be trusted to keep their current consumption within reasonable bounds.  What I'm saying here is that if a short were to happen to occur on this circuit, e.g. if +5 got temporarily shorted to ground, then it would cause the computer power supply to panic and shut off, and that sort of thing would be somewhat traumatic for the computer, and maybe annoying for the user.

Another alternative is to find an inexpensive {+5V, +12 V, gnd} power supply, preferably a small brick-shaped one.  And these are sold for the purposes of powering external hard drives.  Hopefully you can find one of these locally, or in your junk box.  I attached some pictures, just to show what these things look like.

Regarding your circuit diagram, the first picture, the wires from your power supply {+5V, +12 V, gnd} are going to get connected to the nodes labeled {+5V, +13.5 V, gnd} , respectively.

From that same diagram, I am guessing the nodes {Vcc, Data, Vpp, and also gnd} are pins on the PIC microprocessor. 

The IC U1, SN7407N, is some flavor of  hex buffer, you know 6 buffers.  Those are the six triangle shaped things on the diagram.

The following site:
is helpful for looking up unfamiliar parts, like the SN7407N, the 2N3906 transistors,
just so that you know what pin does what, and what each one looks like as a little black plastic box.