Looking for simple current sensing circuit... :)

Much more info required. Give us a complete explination of what is involved e.g. do you want to detect current flowing in a wire, and if so, what is the 'normal' flow? 240v AC, 9v DC, a few microamps from a phono stylus, what?

Without a complete explination (hint: write at least two paragraphs) we can't help you.

Hi there, thanks in advance, I haven't really worked out what current is going to be flowing yet, but at the moment I'm estimating 12V DC at 40-50W, but yeah, it'll be monitor current through a wire, in this instance may be the 12VDC supply line, let me know if you find anything! Thanks!

On Mon, 3 Oct 2005 14:31:56 +1000, "Bill T" put finger to keyboard and composed:

The above circuit is a comparator that tells you when a certain current threshold has been exceeded. Is that all you need, or do you want a readout of the actual current?

If the former, then a simple circuit such as the following may suffice:

PNP transistor E C +V o--|---\___/-----> to overload indicator | | | R | | |-Rs--|------> to load

Note that you will lose up to 0.6V across sense resistor Rs. If the max current is to be 5A, then choose Rs = 0.12 ohm, 5W+.

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.

that'll be all over the place with transistor (expect a 4:1 beta variation from a single manufacturer), temperature and no doubt sock colour.

** Individual transistor beta will have no effect, the circuit operates on device Vbe - you arrogant sheep shagger.

Temperature will increase the sensitivity by 2mV ( or 16mA in this case ) per degree C - likely a trivial amount.

Bet *YOU* have socks of different colours as sizes on each foot.

........ Phil

depends on the load really. If you want an astonishingly crude circuit, then use this one. Beta does count, because the current flowing into the "sensing circuit" is one beta'th of the load current.... say you use a grounded resistor, and a comparator. Then the actual trip point will depend strongly on Beta.

it *wont* provide a nice crisp "switching" action. but often rough enough is good enough.

google SED, there are plenty of good ways to solve this problem. use a single supply opamp with an input common-mode range that includes the

+ve rail. Convert the I*Rsense voltage into a current with a pnp transistor and a resistor. Then feed that current into a grounded resistor, and voila - high-side current sensing. Nice and accurate, stable and repeatable.

Nah, barefoot.

I thought your RMS current meter was pretty good, Phil. Its not quite what I needed though, and I kinda got busy....

Cheers Terry

** Bullshit - you are a pathetic loser.

** Really desperate sheep shagger crapology.

** What **** utter **** bullshit.

** Wot about the gumboots you shove the ewe's hind legs into ?

** Can I expect to see your clones on the NZ market soon ??

........... Phil

What about MAX721, MAX722

On Tue, 04 Oct 2005 16:00:07 +1300, Terry Given put finger to keyboard and composed:

With respect, I think you are having a brain fart. The circuit will do just fine if the OP's requirements aren't too stringent. At the very least it satisfies his requirement for simplicity.

If OTOH he wants something with all the bells and whistles, then he could adapt this design by modifying the front end:

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.

Thanks for the replies guys, I'll been busy, when I'll have time I'll give it a try and see how it goes... thanks