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Design of low current sensor from 50mA to 2A

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areebaa

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hi, I would like to sense the current from a path where a current of 50mA to 2 A is flowing to the load. Can I use simple differential amp with gain across the Rsense =20mohm or is there any contemporary design help.
thanks
 

Assuming this is dc measurement ?

It then depends on if the current shunt is located in the negative or the positive side of the supply, and if positive, how high the dc voltage is.

There are some very nice current shunt amplifiers available from Maxim and Linear Technology, but which one to use depends on the specific application.
 

thank you for your reply actually I would like to measure load current in a dc-dc buck converter.
sequence is
buck output --Rsense 20m ohm ---load 6 ohm---gnd


Assuming this is dc measurement ?

It then depends on if the current shunt is located in the negative or the positive side of the supply, and if positive, how high the dc voltage is.

There are some very nice current shunt amplifiers available from Maxim and Linear Technology, but which one to use depends on the specific application.
 

How about a MAX471 ?

https://pdfserv.maximintegrated.com/en/ds/MAX471-MAX472.pdf

These are listed as not for new designs, but are still available. The advantage is that they are available in an 8 pin plastic DIP. There are plenty of alternatives but most if not all are in very small surface mount packages.

**broken link removed**
 

Hi,

If you can tolerate 500mW of power dissipation at 2A then choose a shunt value of:

R = P / (I x I) = 0.5W / (2A x 2A) = 125mOhms. (Or some other value in this range)

(Use a shunt rated for 1W at least, to avoid high shunt temperature)

This gives a 6 times better (higher) shunt signal than the 20mOhm shunt. Therefore offset errors have less influence.

Klaus
 
Good idea Klaus.

And if you decide to do it that way, a jfet op amp has an input common mode voltage that includes the positive supply rail.
 

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