Author Topic: Dave's EEVblog #577 Precision 1 A Current Source  (Read 2362 times)

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Offline XpLanR4mI

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Dave's EEVblog #577 Precision 1 A Current Source
« on: June 22, 2015, 03:32:13 am »
I'm looking to build a 1 amp current reference Source to be used to calibrate a Data Acq. system. I like the #577 blog, but would like to know if someone might know of an alternate to the Vishay 4-terminal VPR221ZT 1R2500 0.02% current sense resistor, not Vishay, or an alternate circuit which might offer similar specs. The input impedance for the Current transformer is 1M and has 0.1% accuracy so I want to maximize it's capability.

   Thanks :)

Offline zlymex

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Re: Dave's EEVblog #577 Precision 1 A Current Source
« Reply #1 on: March 08, 2016, 11:10:30 am »
Sorry to bring this up, I thought it might be a common interest on how to choose a current sensing resistor of 1A or above.

Firstly, I have made an ultra-stable 1A current source prior to Dave's video, using similar Vishay precision shunt(Vishay VHP4 0.1 Ohm). I achieve this sub-ppm short term stability also by lowering the shunt resistance, low noise opamp and especially heat management combined.

Secondly, lower the sensing voltage from 1.25V to 0.2V/0.25V will increase the stability significantly. the voltage reference needed can be divided from a 1.25V or 2.5V Vref. Thus, an 0.2 Ohm or 0.25 Ohm resistor is required for 1A current source. For 2A or 10A current sensing, the voltage can be further reduced to 0.1V.

Thirdly, make a large heatsink for the sensing resistor. I often use the aluminium case for the heatsink.

Fourthly, move the power MOS(probably the most heat generator) outside the case like I did. Also the power supply could be a separate unit. Mine is battery powered.

And lastly, some none-Vishay sense resistors
1. Alpha Electronics, they make very good shunt resistors widely used among Japaneses instruments.
2. Isabell**, famous for precision shunt, their PBV is nice for current sampling.
3. Dale resistors, 2 wire, if the requirement is not very tight
4. Use parallel. ex 20 foil resistors of 5 Ohm, similar to Fluke A40B, where they use 960 foil resistors to measure 100A current.

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