techniques for sensing fairly small currents (<1A)

"Michael"

** No.

Try looking for " Hall effect sensors " and current transformers.

The former operate with AC and DC currents while the latter are AC only.

Both are non contact ( aka galvanically isolated) sensing methods.

...... Phil

Hi Phil - I should mention I'm only interested in DC current sensing.

I'm aware of hall effect current sensing - but isn't that only viable for large currents? A quick google only finds parts designed for larger current ranges than what I'm interested in.

-Michael

"Michael" "Phil Allison"

** Most linear Hall effect sensors work down to the 1 mA level, just ne - Lem, Honeywell etc.

All YOU need do is run a few turns of insulated wire through the hole to increase the sensitivity.

...... Phil

Keep in mind that many other components, such as FETs, can look a lot like resistors, and the addition of a dedicated part may not be necessary.

Why do you prefer high-side to low-side?

Hmm, this is a valid point. The power board will just be stepping down a large DC voltage to various smaller DC voltages - so there very well might be a good component to grab a current reading from. I'll have to look into that further when the design is farther along.

So that I can use a shared ground.

-Michael

IANEE, but not really counter-intuitive IMO. He wants the grounded side of his stuff to all be at the same potential, ground. :-) If all his stuff ran on a kajillion volts, he probably wouldn't want the grounds to all be thousands of volts apart from each other. ;-)

High side current sensing requires more complicated circuitry than sensing at ground, but if that's what you want here are a couple of ideas. I'm praying the ASCII comes out ok, because I'm using groople and they seem to have eliminated the fixed font feature. Thank Winfield Hill for the first one and Fred Bloggs for the second.

• -----+--- Rsense ----+---->

. | | . Rc | . +------------, | . | __ | | . c\| / +|--' | . NPN |---< | | . e/| \_-|-----' . | . Rload . | . - -----+-------------------->

. . .---------------------. R1 . | | 1.24V - (Vled-Vbe)*----- . | | R2+R1 . ----+-----[Rs]------+-------> I= ---------------------- . | | | Rs* R2/(R1+R2) . | | | . | | | . | [R1] | . | LM185 | | . --- | | . / \ -------------+ --- . --- | \ / led . | | --- . [R4] [R2] | . | | | . | | | . +---------------' | . | | . | | . | | . >| | . |-------------------+ . /| | . | | . +---> to comp [R3] . | | . [Rc] | . | | . --- --- . .

Exactly. Even though everything is fairly low voltage, I still have a number of supply lines on the same board. If I were to sense ground currents I'd have to have a separate ground for each voltage - while now I just have one big ground plane.

-Michael

Yep- that's basically it, convert the current to a voltage with something called a resistor. The actual circuitry to do this will be a function of your intended use. For example are you monitoring for a trip or foldback threshold , or are you monitoring for a measurement to be displayed, or are you monitoring for some other purpose, and if so, then how much range do you need i.e. 10:1, 100:1, 1000:1 etc. As usual we will be standing by to give you the best possible answer, as well as including a compendium of 10,000 ascii art drawings of typical circuits if that's what you desire. We aim to please you in every way possible and eagerly await your evaluation of our performance, maybe even declaring one or the other of us a "winner," the ultimate purpose of our existence...

Hi Michael I have used some highend sensor-ic's from Maxim try search for high end sensors at maxim.. they can do what you need. alex

Hmm - unfortunately I cannot declare you the winner, as you just restated my original question as a statement, with a condescending tone as an added bonus. Better luck next time!

-Michael

AWWWWWWWWWWWWWWWWWW...shucks!

a power board that needs to monitor currents on a

Hi Alex - that sounds like exactly what I'm using right now. I'm using MAX4372H high side current amplifiers. I would just prefer to find a solution that didn't require shunt resistors.

-Michael