inductance of SMD 2W milliohm resistor

zilog · 30th August 2006, 11:54 AM

I am trying to choose between using 47 mOhm SMD resistors (2W) and corresponding current sensing shunts for overcurrent sensing in a class d output stage. Shunts have very low inductance (basically just 20 mm of straight wire), but what is the inductance of the typical SMD resistor (how are they internally constructed)?

I have bad experience when it comes to inductance in axial 47 mOhm "non-inductive" resistors, so I want to know if my design is forced to use expensive shunts, or if I can manage with resistors without too much sacrifice in inductance.

sawreyrw · 30th August 2006, 10:06 PM

The inductance of wire over a grond plane should be well under 20 nH/inch, so the inductance of a 2W SMD is negligable. (I can't imagine this is a wirewound resistor.)

jackinnj · 30th August 2006, 11:10 PM

and don't forget that the impedance of the inductive part is swamped by the d.c. resistance and that the PCB material becomes conductive around a few hundred MegaHertz due to parasitic capacitance

30th August 2006, 11:54 AM	#1
zilog diyAudio Member Join Date: Oct 2005	inductance of SMD 2W milliohm resistor I am trying to choose between using 47 mOhm SMD resistors (2W) and corresponding current sensing shunts for overcurrent sensing in a class d output stage. Shunts have very low inductance (basically just 20 mm of straight wire), but what is the inductance of the typical SMD resistor (how are they internally constructed)? I have bad experience when it comes to inductance in axial 47 mOhm "non-inductive" resistors, so I want to know if my design is forced to use expensive shunts, or if I can manage with resistors without too much sacrifice in inductance.

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30th August 2006, 10:06 PM	#2
sawreyrw diyAudio Member Join Date: Apr 2006 Location: Minnesota	The inductance of wire over a grond plane should be well under 20 nH/inch, so the inductance of a 2W SMD is negligable. (I can't imagine this is a wirewound resistor.)

30th August 2006, 11:10 PM	#3
jackinnj diyAudio Member Join Date: Apr 2002 Location: Llanddewi Brefi, NJ	and don't forget that the impedance of the inductive part is swamped by the d.c. resistance and that the PCB material becomes conductive around a few hundred MegaHertz due to parasitic capacitance

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