Author Topic: op amp current sense amplifier.  (Read 323 times)

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Online m3vuv

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op amp current sense amplifier.
« on: December 21, 2018, 07:37:43 pm »
hi all,im after using an op amp as a current sense amp on a psu,30v max output,the op amps i have are jrc4558 ic's,the max supply voltage is 18v,i wanted to use them from the same power rail as the psu,obviously i cant do that,now the question is can i power it from say a lm 7824 reg?,the differential voltage is 30v max,can the voltage at the current sense resistor be higher than the op amp supply voltage?hope that makes sense,cheers m3vuv.
 

Online Zero999

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Re: op amp current sense amplifier.
« Reply #1 on: December 21, 2018, 08:33:55 pm »
What makes you think the JRC4558 is only rated to 18V? The data sheet says +/-22V, which is a total supply voltage of 44V.
https://img.ozdisan.com/ETicaret_Dosya/408213_9227758.pdf

The maximum differential voltage rating is 18V, so make sure the voltage between the inputs stays below that and it will be fine.

The common mode range doesn't include either supply rail and is specified at ±12V worst case, with a +/-15V supply, so the voltages at both input pins should be over 3V or more from either supply rail, for it to work properly. This means if the power supply voltage is 30V, the voltages at the inputs must range from 3V to 27V, in order for the op-amp to work. This could be an issue if the current sense resistor is on either rail. One way round this is to power the op-amp from the unregulated voltage and put the current sensor on the output, which will always be a few volts lower.
 

Offline Simon

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Re: op amp current sense amplifier.
« Reply #2 on: December 22, 2018, 03:21:39 am »
Please do not post the same topic twice!
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Varied stock of test instruments and components including EEVblog gear.
Also, if you want to get ripped off: https://www.ebay.co.uk/usr/simons_electronics?_trksid=p2047675.l2559
 


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