Author Topic: Why would you need a precision 1A current source?  (Read 610 times)

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Offline bsodmike

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Why would you need a precision 1A current source?
« on: February 24, 2020, 01:08:14 pm »
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!
 

Offline Gyro

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Re: Why would you need a precision 1A current source?
« Reply #1 on: February 24, 2020, 01:58:02 pm »
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.
« Last Edit: February 24, 2020, 02:00:46 pm by Gyro »
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Online exe

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Re: Why would you need a precision 1A current source?
« Reply #2 on: February 24, 2020, 02:05:48 pm »
In the era of digital calibration one would want a stable current source.
 

Online Mechatrommer

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Re: Why would you need a precision 1A current source?
« Reply #3 on: February 24, 2020, 02:07:59 pm »
to check current measurement device such as DMM is within spec (Transfer Standard)
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Online BravoV

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Re: Why would you need a precision 1A current source?
« Reply #4 on: February 24, 2020, 02:16:33 pm »
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.

Online exe

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Re: Why would you need a precision 1A current source?
« Reply #5 on: February 24, 2020, 02:27:06 pm »
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"...
 

Offline Vovk_Z

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Re: Why would you need a precision 1A current source?
« Reply #6 on: February 24, 2020, 06:51:00 pm »
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.
 

Online Mechatrommer

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Re: Why would you need a precision 1A current source?
« Reply #7 on: February 24, 2020, 08:22:24 pm »
yeah but building good reference need good T&M equipments in the first place, hobbiests can build whatever they like.
if something can select, how cant it be intelligent? if something is intelligent, how cant it exist?
 
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Offline angrybird

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Re: Why would you need a precision 1A current source?
« Reply #8 on: February 24, 2020, 10:43:23 pm »
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.
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Online Yansi

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Re: Why would you need a precision 1A current source?
« Reply #9 on: February 24, 2020, 11:21:57 pm »
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.
 

Offline angrybird

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Re: Why would you need a precision 1A current source?
« Reply #10 on: February 24, 2020, 11:27:17 pm »
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".

 :D
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Offline bsodmike

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Re: Why would you need a precision 1A current source?
« Reply #11 on: February 26, 2020, 04:01:14 pm »
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).
 

Offline bsodmike

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Re: Why would you need a precision 1A current source?
« Reply #12 on: February 26, 2020, 04:02:14 pm »
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!
 


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