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kislay verma
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Join Date: Jun 2012
Location: Guwahati,India
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Current Sensing

08/02/2012 2:11 AM

I am making a buck converter designed for a fixed value of output current (10-15A).

For this I have to make a current sensor circuit which senses the current and feeds to PWM controller. The problem is to make a current sensors.Please suggest ways for sensing such high currents and that can be fed into a micro-controller which can accept only voltage in the range of 0-3.3V.

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satendrakumart
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Join Date: May 2011
Posts: 61
Good Answers: 1
#1

Re: current sensing

08/02/2012 5:44 AM

Use a "shunt resistor" as used in ammeters in series with your load.

or a DCCT (series resistor used in DC Drives for current feedback)
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Winfield Hill
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#2

Re: Current Sensing

08/02/2012 9:15 AM

Most of us use low-value resistors, you can get 0.01 ohms or lower (DigiKey offers down to 4mΩ). 10mΩ would give you a reasonable 150mV drop at 15A, and dissipate under 0.5W for a 15A ramp at 50% duty cycle. That's a Rohm 2512 size, 2W part in the photo.

What controller ICs are you thinking of using?

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leveles
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Join Date: Jan 2008
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#3

Re: Current Sensing

08/02/2012 10:43 PM

Winfield is correct for the milliohm resistors. However, the Ground's resistance and ground bounce has to be taken into account.

On the other hand, Hall effect sensor output is readily adiusted with resistors. And Its current sensitivity is set by its distance to the wire.
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WAWAUS
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Join Date: Aug 2010
Location: Melbourne, Australia
Posts: 740
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#4

Re: Current Sensing

08/02/2012 11:20 PM

suggest you search 'high side current shunt' or ' low side current shunt'
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sawmilleng
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Join Date: Dec 2006
Location: In the sticks of the Central Kootenays, BC, Canada
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#5

Re: Current Sensing

08/02/2012 11:53 PM

Use a Hall effect sensor. They are set up for the job and you can purchase one in the current range you require. Go to Digi-Key or similiar suppliers and search for "Hall effect current sensor" Or search Globalspec!

Jon.
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uli_newBuilder
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Join Date: Dec 2009
Posts: 87
Good Answers: 5
#6

Re: Current Sensing

08/03/2012 4:51 AM

Hello, there are god recommendations to use a shunt resistor to measure the current. High power, low ohmic shunt resistors are hard to get and expensive.

But you can use an off the shelf Power Mosfet - make sure that via the gate drive voltage it is fully conductive and -viola- you have a high power resistor with a low resistance / sufficient power rating which is given by the selected MOSFET type. 4mOhms - no problem, just look through the catalog for Rds_on. And in most cases this is really cheaper and easier to get than comparable passive components. or power sensor ICs.
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WAWAUS
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Location: Melbourne, Australia
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#8
In reply to #6

Re: Current Sensing

08/05/2012 7:01 PM

We use current sense resistors in the range 0.01 to 0.2 Ohms frequently enough to be able to say that they are readily available from Digikey, Mouser, etc and are NOT expensive.
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The Shadow
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Join Date: May 2012
Location: Sutter buttes - East 50 miles you found me
Posts: 59
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#7

Re: Current Sensing

08/03/2012 8:07 AM

Why make what you can buy cheap?

Go to the link below and check these out.

http://www.veris.com/Category/Current-spcMonitoring.aspx

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leveles (1); satendrakumart (1); sawmilleng (1); The Shadow (1); uli_newBuilder (1); WAWAUS (2); Winfield Hill (1)

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