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DIY electronic load

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Mosaic

Well-Known Member
Hi All:
I am designing a DC electronic load (perhaps up to 4A @ 30VDC) and I hope to add Constant current, Voltage & Power via a data logging uC approach.
4A = 16W dissipation via a 1 ohm , current sense, load resistance. Perhaps 5 parallel 5W wirewound, 1 ohm units used here.
A half amp 'low' range with a 10 ohm 5 W wire-wound load as a current sense => 10mV per mA for op amp amplification to feed the uC ADC.
Also with a resettable minimum voltage trip off and external cmos logic start & stop load triggers.
I hope to use it for general PSU design load testing and battery mAh profiling.

I want mA accuracy in the half amp range, which means a decent low offset, precision , current sense, op amp. I am open to suggestions please.

I did locate this one:
https://www.jameco.com/Jameco/Products/ProdDS/904798.pdf
@ a tiny 1 uV typical input offset, but only 2.7V - 5.5V supply

and this one ..about 60uV to 90 uV (grade C) typical input offset with a 5V - 15V supply.
https://www.jameco.com/Jameco/Products/ProdDS/239169.pdf

With a 10mV / mA signal does the LT1013CP seem adequate to feed the uC ADC an amplified current sense V?
It's about half the price of the 1uV offset OPA.
 
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5 parallel 1 ohm resistors give 0.2 ohms resistance. Is that what you want?

The LT1013C has a maximum offset of 0.3mV at room temp. That would give a maximum error of 30uA with a 10mV / mA sensitivity. Is that adequate for your needs?

Unless you are building a bunch of these I wouldn't think the cost of the op amp would be a significant factor.
 
I meant 5, 5 ohm current sense units.:(

Thx for your input!
 
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Could you just close a constant current loop in hardware then just set current with the micro. Then the op amp offset isn't amplified.
The sense resistor could be a little problem, but could probably be calibrated if it's a onesie.
 
I simulated a 150Khz PWM 'load' smoothed via an inductive pi filter as a means to decrease heating in the LOAD Fets.
I notice for a 120Hz DC ripple input that there is a phase change with the current vs voltage. Would this be of significance in doing CC, CV and CR for a single phase system?
 
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