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Current Sensing Circuit Concepts and Fundamentals

Authored on: Jul 5, 2010 by Yang Zhen

Technical Paper / Application Note

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This application note focuses on the concepts and fundamentals of current sensing circuits. It introduces current sensing resistors, current sensing techniques and describes three typical high-side current sensing implementations with their advantages and disadvantages.



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GREATTerry Posted Jul 20, 2010

I personally think this is just an entry level circuit discussion article with very limited information. The article just mention about the sense resistor approach while there are indeed many other current methods that wasn't discussed. Besides, building instrumentation amplifier (IA) with discrete op-amp is not as easy as the simple equations. There are many other practical stuff (including layout) that must be considered. There are many monolithic IA that can do a much better. For high side sensing, there are also some specially design current sense amplifiers that are even better then an IA.

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David Ashton Posted Jul 31, 2010

Terry...someone is listening to you...see http://www.eetimes.com/design/automotive-design/4010355/Understand-low-side-vs-high-side-current-sensing

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rabisnkr Posted Oct 8, 2010

Yep Terry, agree with you. Thanks Asho-#1. Wish someone would take it to the next logical level. We have a need for current sensing in an application where, due to device dimensions, the actual "processing" has to be done a few meters away from the sensor per se. Been a nightmare, given the electrically noisy environment in which this is supposed to operate. Any pointers?

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rickyc Posted Aug 18, 2010

thanks

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Technology trends Posted Aug 19, 2010

hi whether it is possible to connect this circuit with an wireless network

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sby Posted Aug 25, 2010

I concur with GREAT-Terry. This article barely passes as students' term paper. Not mentioning dedicated products for current measurement is unacceptable. On the positive side, this is at least an objective article rather than the sale pitch by Maxim pointed out by Asho_#1.

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jmpearson Posted Aug 25, 2010

Whereas the resistor approach may be fine for some applications, I implemented a better solution for my 300KHz, +/-150V, 1000W half bridge application. A small gapped powdered iron core with a hall effect sensor stuck in the gap with a few windings (opposite directions)worked great and was cheap. Put this module in between the high & low side FETs on the output of the bridge to measure bridge current in either direction. The Hall Effect sensor output fed into a general purpose ground-referenced op amp to scale the voltage to whatever you needed. It was fast enough to use for overcurrent protection, didn't introduce any additional resistance, and generated a nice robust output voltage in proportion to the bidirectional half-bridge current.

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asangoi Posted Aug 26, 2010

Here's a simple and cost-effective solution to high-side current sensing. http://www.supertex.com/pdf/datasheets/HV7801.pdf No complex instrumentation amps needed!

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DHambley Posted Aug 27, 2010

For a kid right out of college, this article may confirm that the basic op-amp circuits he learned are valid. For real-world applications however, the article does not educate the reader. Problem areas such as the inductance of low-R CS resistors when used for high-bandwidth sensing, for example, are not even mentioned.

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n9wbj Posted Sep 1, 2010

Thank You

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Bhola_#1 Posted Sep 19, 2010

Good article for entry-level graduate to play with some simulator such as LTspice or other spice simulator to get more indepth knowledge of circuits.

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Canop Posted Sep 22, 2010

Really good article thanks!

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Robotics Developer Posted Sep 22, 2010

I would like to thank both the poster of this article and those who contributed both pointers and questions! It really helps to get multiple points of view on a subject. Reading the application note and following the other links gave me a better appreciation for what designers are up against.

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Larry0 Posted Sep 23, 2010

Exide has been using low side sesnsin in their automotive battery chargers for years.

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Scientist Posted Oct 14, 2010

some lab stuff with it?

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t.alex Posted Nov 21, 2010

Even though simple and fundamental, I believe the article is worth reading, especially for someone who is not so familiar with the analog aspect of designs.

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Robotics Developer Posted Dec 13, 2010

I would say a nice general overview of current sensing topologies, thanks! I wonder how much the circuit outputs would be affected by say high frequency switching (say PWM based motor control) and back EMF from motor operation. Would filtering be needed or just helpful in these situations with motors/PWM switching?

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Jonathan Allen Posted Jan 21, 2011

I am not sure what the author means by "low to medium current" but for the past 100 years, companies like Weston and Simpson have been making current sensing shunts with full scale voltage drops of 50 mV for for current ranges up to at least 1000 amps.

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ultimateanalog Posted Sep 4, 2011

The article is very good and helpful, many guys just overlooked the fudamentals which actually is the most important thing. Thanks for the posting.

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Chuck Sampson Posted Apr 4, 2012

The title of the article is "Current Sensing Concepts and Fundamentals". What part of concept and fundamentals do people not understand? I think those people were looking for the article "Advanced Current Sensing Techniques" which I haven't found yet. Actually I could and probably should write one. Anyway, nice article.

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Robotics Developer Posted Jun 13, 2012

Well I am sure that an Advanced Current Sensing Techniques article would be most helpful, I would be very happy with an article titled: " Practical real life current sensing/measurements implementations (in noisy environments - maybe also?)"

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Phluph Posted Jun 28, 2012

... Um, so what's with this spate of articles on par with high-school level electronics 101? For what is covered - good job but, is someone trying to make up for what is no longer really taught in college (for late starters) anymore? Ya know, analog stuff?

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