Why would you need a precision 1A current source? - Page 1
Forum section: electronics / beginners

author: bsodmike
author_rank: Regular Contributor
timestamp: February 24, 2020, 01:08:14 pm
content: Hi all,Having watched Dave's series on building a precision 1A current source, what are real-world examples for needing something like this?Thanks!

author: Gyro
author_rank: Super Contributor
timestamp: February 24, 2020, 01:58:02 pm
content: Measuring very low value resistors. 1mR at 1A gives a reasonably measurable 1mV voltage drop.'Resistors' doesn't just mean resistors btw, it could be wiring, PCB traces (and shorts) switch contacts, windings, etc.

author: exe
author_rank: Unknown
timestamp: February 24, 2020, 02:05:48 pm
content: In the era of digital calibration one would want astablecurrent source.

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 24, 2020, 02:07:59 pm
content: to check current measurement device such as DMM is within spec (Transfer Standard)

author: BravoV
author_rank: Super Contributor
timestamp: February 24, 2020, 02:16:33 pm
content: Quote from: Gyro on February 24, 2020, 01:58:02 pmIn the old days when I only have a cheap DMM, not the fancy 4 wires measurement, the diy 1A current source was handy for testing crappy power cord.

author: exe
author_rank: Unknown
timestamp: February 24, 2020, 02:27:06 pm
content: Quote from: Mechatrommer on February 24, 2020, 02:07:59 pmIsn't it better to check values at the top of the range? Say, for a 3A range, to check a full-scale error, one would want a 2.9A source, or 3A source if DMM supports "overrange"...

author: Vovk_Z
author_rank: Super Contributor
timestamp: February 24, 2020, 06:51:00 pm
content: If you know how to build precision 1 A current source - you can build 3 A source too.And 1 A is very universal value and is ok for 2-4 A ranges.

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 24, 2020, 08:22:24 pm
content: yeah but building good reference need good T&M equipments in the first place, hobbiests can build whatever they like.

author: angrybird
author_rank: Regular Contributor
timestamp: February 24, 2020, 10:43:23 pm
content: Any good LED driver is a constant current source. This control scheme is more complex (more rewarding to understand!) than a typical run of the mill voltage mode converter.You don't need high end test equipment to build and calibrate a current source, just a decent multimeter with good accuracy in the mV range and a precision shunt. Your accuracy is only limited by the meter.

author: Yansi
author_rank: Super Contributor
timestamp: February 24, 2020, 11:21:57 pm
content: Nope.How about verifying temperature stability? How about short- and long-term stability of the source (noise, drift)? Single simple multimeter measurement won't cut it.

author: angrybird
author_rank: Regular Contributor
timestamp: February 24, 2020, 11:27:17 pm
content: Sorry I wasn't clear. I was talking about characterizing the output current. You don't need high end test equipment to do this. You can get a precision shunt for a rather good price, and from there your accuracy of measurement is limited only by your multimeter, and maybe the small temperature coefficient of the shunt (though I would presume that most people at home are in "room temperature".

author: bsodmike
author_rank: Regular Contributor
timestamp: February 26, 2020, 04:01:14 pm
content: Quote from: Mechatrommer on February 24, 2020, 08:22:24 pmMy thinking exactly; I've got a couple Fluke DMMs but I don't have a trusted source to reference/verify a 1A precision source. I'm planning on building one soon though (as a learning exercise).

author: bsodmike
author_rank: Regular Contributor
timestamp: February 26, 2020, 04:02:14 pm
content: Quote from: angrybird on February 24, 2020, 10:43:23 pmAha, good to know, thanks!