possible to use Rds(drain to source) as a shunt to measure current across MOSFET?

Thread Starter

ak52

Joined Oct 15, 2014
195
Hello Everyone,

Would it be a good idea to use the internal Rds of a MOSFET as a high side shunt. or would it be better to get a dedicated shunt resistor separately to measure current passing though the MOSFET?

Thanks ,
AK
 

WBahn

Joined Mar 31, 2012
24,970
You need a resistance that is a known and stable value. It is unlikely that a channel resistance of a FET is going to qualify.
 

Bordodynov

Joined May 20, 2015
2,454
Some DC/DC stabilizers on-resistance of the transistor is used to limit the current.
In this case, voltage control is performed in the open transistor.
 

crutschow

Joined Mar 14, 2008
23,751
The Rds ON of a MOSFET varies significantly from unit-to-unit and also has a positive coefficient with the MOSFET junction temperature.
So Rds would not be good for the purpose of measuring the MOSFET ON current unless your accuracy requirements are very low.
 

WBahn

Joined Mar 31, 2012
24,970
Some DC/DC stabilizers on-resistance of the transistor is used to limit the current.
In this case, voltage control is performed in the open transistor.
But performing current limiting is very different from performing current measurement.
 
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