Looking for current sensing IC - Electronic Circuits Projects Diagrams Free

DWE&C · 8th June 2007, 03:33 AM

I'm looking for an IC or other small inexpensive device that will detect a 12V DC current flow of perhaps as much a 2 amps. I'm just formulating ideas and have not gotten to the point of actually calculating or measuring the current. Device doesn't need to measure the current, just needs to detect current.
All help appreciated.

justDIY · 8th June 2007, 03:40 AM

what do you mean detect?

if it's 12v DC, just hang NPN transistor from it, referenced to ground (if you use a bjt be sure to use a generous base resistor) - when current is present, the transistor will turn on, no current, transistor off

alternately you could hang an optoisolater from the 12vdc (again, resistor) - current, opto output low, no current, opto output high (assuming a typical inverted opto)

I don't think DC can be sensed from induction, so you'll have to put a shunt in series with the load to actually measure the current.

I2R tells us 2 amps will generate 400mW across a 100mOhm shunt, dropping 200mV - hook that into an op-amp and boost the voltage a bit and you've got a simple ammeter

Sceadwian · 8th June 2007, 03:46 AM

Sensing the voltage drop across the load itself might be an option without a shunt. You need to more throughly qualify at exactly what point (how many Amps) you'll consider the load to be 'on' If the device has an idle current of 200ma's and you don't consider that on it needs to be taken into acount when measuring the circuit. If you can describe a couple impedance states (such as idle 200ma's of current startup 500ma's of current running 2amps) and what the power supply impedance is then it's just a matter of calculating the right voltage divider for a comparitor setup across the load.

on1aag · 8th June 2007, 06:19 AM

Hi DWE&C,

Take a look at these application notes:

http://www.maxim-ic.com/appnotes.cfm/an_pk/1180

http://www.maxim-ic.com/appnotes.cfm/an_pk/478

http://www.maxim-ic.com/appnotes.cfm/an_pk/3331

http://www.maxim-ic.com/appnotes.cfm/an_pk/3883

http://pdfserv.maxim-ic.com/en/an/AN3883.pdf

http://pdfserv.maxim-ic.com/en/an/AN3669.pdf

on1aag.

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8th June 2007, 03:33 AM	(permalink)
DWE&C	Looking for current sensing IC I'm looking for an IC or other small inexpensive device that will detect a 12V DC current flow of perhaps as much a 2 amps. I'm just formulating ideas and have not gotten to the point of actually calculating or measuring the current. Device doesn't need to measure the current, just needs to detect current. All help appreciated.

8th June 2007, 03:40 AM	(permalink)
justDIY	what do you mean detect? if it's 12v DC, just hang NPN transistor from it, referenced to ground (if you use a bjt be sure to use a generous base resistor) - when current is present, the transistor will turn on, no current, transistor off alternately you could hang an optoisolater from the 12vdc (again, resistor) - current, opto output low, no current, opto output high (assuming a typical inverted opto) I don't think DC can be sensed from induction, so you'll have to put a shunt in series with the load to actually measure the current. I2R tells us 2 amps will generate 400mW across a 100mOhm shunt, dropping 200mV - hook that into an op-amp and boost the voltage a bit and you've got a simple ammeter __________________ If you don't have a planet, what good are gold bars? want to contact me directly? gmail gordonthree check out my project website: http://projects.dimension-x.net Favorite numbers: 09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0

8th June 2007, 03:46 AM	(permalink)
Sceadwian	Sensing the voltage drop across the load itself might be an option without a shunt. You need to more throughly qualify at exactly what point (how many Amps) you'll consider the load to be 'on' If the device has an idle current of 200ma's and you don't consider that on it needs to be taken into acount when measuring the circuit. If you can describe a couple impedance states (such as idle 200ma's of current startup 500ma's of current running 2amps) and what the power supply impedance is then it's just a matter of calculating the right voltage divider for a comparitor setup across the load. __________________ "Because I be what I be. I would tell you what you want to know if I could, mum, but I be a cat, and no cat anywhere ever gave anyone a straight answer, har har."

8th June 2007, 06:19 AM	(permalink)
on1aag	Hi DWE&C, Take a look at these application notes: http://www.maxim-ic.com/appnotes.cfm/an_pk/1180 http://www.maxim-ic.com/appnotes.cfm/an_pk/478 http://www.maxim-ic.com/appnotes.cfm/an_pk/3331 http://www.maxim-ic.com/appnotes.cfm/an_pk/3883 http://pdfserv.maxim-ic.com/en/an/AN3883.pdf http://pdfserv.maxim-ic.com/en/an/AN3669.pdf on1aag.