Current limiting with an visual indicator of overload

As far as I am aware AT PSU don't have any SC protection but ATX PSU do !

--
Best Regards:
                     Baron.

"OBones"

** The supply has a lamp ( ie a 12 volt, 21 watt car brake lamp ) in series with the output. ** Why not start with a lamp or two ? 6 volt for the 5 volt rail and 12 volt for them.

..... Phil

Wouldn't the voltage drop modify the output voltage even for low currents? I mean, the point is indeed to lower the voltage when there is a lot of current going through, even to the point that there is not enough voltage anymore for the circuit, but what about normal operating conditions?

Try this:

This even gives you an output current. You may have to amplify it depending on the light indicator you choose.

Regards

-- Bill Naylor

Electronic Kits for Education and Fun

** Nope.

Lamps have a low resitance at low current levels - about 12 times less than at rated current.

How do you think that lamps in series with model railway boxes work ??

BTW:

You are ***way*** over snipping.

Makes you look like a context shifter.

IE, the lowest scum on usenet.

..... Phil

that

Why not use a 7812 and 7805 to protect the supply against short- circuits ?

The light (in series with the supply) is the current limiter, in the system you describe. They work quite well, though of course they do not have a hard response (ie, if you are limiting to 5 amps at 5 volts, you're not going to have 4.9 amps at 5 volts - in particular, you won't have 5 volts out the far side of the lightbulb at 4.9 amps.) But for typical bench supply use, this is not usually a problem. In fact you can set up a lamp board where you switch in or out various bulbs based on what you expect the load to be (and thus where you want to limit the load to). Old fashioned but still works perfectly well.

Various versions of far more complex "modern" circuits could achieve a similar function with a harder response.

An ammeter (fairly inexpensive ones are not too hard to find) and a fuse or circuit breaker work perfectly well, too, without much complexity.

--
Cats, coffee, chocolate...vices to live by

You need some headroom (Vin > Vout) with those chips. The 7812 won't work with +12 Vin. You could use the

7805 with Vin of 12 volts, but you make extra heat in the chip with a 7 volt Vin-Vout difference.

Ed

they typically are, they'll shut down and need to be power-cycled if you short the +5 or +12

use an automotive headlamp in series with the 12V

for the +5V you'll probably want a lower voltage lamp.

you could use nichrome wire instead of lamps, it lights up with high current too!

Thanks for the suggestion, I'll look into it.

Thanks, it looks interesting, and the application notes around it provide a good starting point