Why would you need a precision 1A current source?

[bsodmike]

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!

[Gyro]

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.

[exe]

In the era of digital calibration one would want a stable current source.

[Mechatrommer]

to check current measurement device such as DMM is within spec (Transfer Standard)

[BravoV]

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.

In 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.

[exe]

to check current measurement device such as DMM is within spec (Transfer Standard)

Isn'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"...

[Vovk_Z]

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.

[Mechatrommer]

yeah but building good reference need good T&M equipments in the first place, hobbiests can build whatever they like.

[angrybird]

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.

[Yansi]

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.

[angrybird]

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".

 

[bsodmike]

yeah but building good reference need good T&M equipments in the first place, hobbiests can build whatever they like.

My 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).

[bsodmike]

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.

Aha, good to know, thanks!