Emergency zero to five V source.

[mixedgas]

Every once in a while some one contacts me who does not do electronics for a living with a emergency need for a schematic.
These I do in Windows Paint, and I refer to them as done in " Walleye Vision.". See the Movie Hotshots Part Deux for the quote.
It refers to a wide eyed fish from my home state of Ohio.

NOTE: Mega Edit,

I'm in Florida when I posted this, chasing after a wonderful gal.
I didn't have time to draw, but I always help my friends in need.
So I get a nice PM and attached was a proper drawing.

EKeefe took the time to do it up right, and that is what is attached.


Steve

[glorocks]

Sometimes you do them on napkins.

[dnar]

Thats how Spinal Tap design their stage sets.

[glorocks]

It might be prudent to put some bypass caps around the reg. chip, especially if the leads are longer than a few inches. A 1 uF tantalum at the input and a .1 uF ceramic on the output would be about minimum. I always put both on the input and output of the regulator.
J

[Photonbeam]

Is there really a chance for oscillations when the input is a battery?

[mixedgas]

Is there really a chance for oscillations when the input is a battery?

No, not all. He's not loading it and I've never had. '05 oscillate.

Steve

[The_Doctor]

It's likely got internal circuitry aimed at making it really easy to use, so while it's a high gain device its sensing input is solidly grounded. I doubt it could oscillate unless that wire was a long one, allowing inductive or capacitative coupling. When fixed regulators are used to make higher voltages than the lowest possible (equal to rated volts), oscillation may be a risk, depending on how resistors are used.

If the output really isn't to be loaded, then a current limit resistor feeding a 5V1 zener might be enough, it has the lowest temperature coefficient of any voltage zener in its standard range, and if the 0.1V extra matters, a small fixed resistance on the high side of the pot could eat that. Better yet, a couple of 2.5V references in series replacing the zener..

[dilbert]

Even on batteries if that's the 'original' 1970's 7805 then the decoupling cap on the output is recommended for stable operation. Some more recent variants & LT's don't need hence the confusion.

[mixedgas]

Even on batteries if that's the 'original' 1970's 7805 then the decoupling cap on the output is recommended for stable operation. Some more recent variants & LT's don't need hence the confusion.

The sole purpose of this was to create a simple quick source. Not a bench instrument.

LM7805 is cheaper then a Zener + Resistor.
Sad but true.

The person who needed this has determined his laser is analog.

GAME OVER.

Steve

[dnar]

I am glad this is cleared up, the OP had me wondering what drugs you were on!