Switching Low Voltage with High Voltage

[Memphetic]

Hey guys. The problem is this: I need a source of 5V OR 12V (it has the ability to be both, depending on the application) to switch 5V.

I would use a LDO regulator, but I don't believe they switch fast enough - the source voltage is actually a digital data signal at 15k baud.

Another thing out the window would be a voltage divider - it would work if I was only working with 12V, but obviously, I wouldn't want it to divide the signal voltage if it's only a 5v source.

I can't think of a way to make an NPN work either... Perhaps I could use a voltage divider on the base to drop the voltage to 1/4 (so we'd be dealing with 1.25v and 3v instead).

Any ideas? Thanks!

[David_AVD]

Input switches an NPN transistor that in turn switches a PNP transistor to get you back to +ve switching.  Pretty standard arrangement.

[daveatol]

Or simply use a series resistor (to control max current) and clamping diodes (to clamp it to 5V).

[Paul Price]

If you take a minute to sketch and carefully describe what your circuit needs to do on a piece of paper and scan it into your computer you can easily create a .jpg or .png picture that would carefully explain what you are trying to do if you can bother attach it to your reply.

Your description of the problem is very vague and part of you description are very hard to understand, but a diagram like this with some words would help to very quickly solve this problem..