INA 122 as current shunt monitor

[dmta]

Hi all,

I want to use the INA122 as a current shunt amplifier. I have attached the schematic here. I want to know before I connect this to power whether it is correct or not. The two diodes are to drop the voltage to the + and - pins by about 1.2V

BTW when I simulate the circuit it does not work !!!!!!!!!!!!!!!!

 

[FvM]

The common mode range is exceeded in the circuit, instead of adding more artificial voltage drop, you should better use a dedicated high side current sense amplifier. 36 V supply is INA122 maximum rating, good design praxis suggest to choose a lower actual supply voltage.

 

[schmitt trigger]

You are missing the gain resistor. That could be the reason it does not work.

Having said that, instrumentation amplifiers have excellent CMRR, but have much tighter constraints with respect to valid common-mode ranges; and they vary with the gain setting. There are tables which show this in the datasheet.

So, as FVM mentions, a dedicated high side current sense amp would be a better option.

 

[zuzu]

I used a dedicated INA169 with excellent results, up to 42V. For lower Vdd use INA149. There are also very good circuits from Linear and others (Zetex, etc).
If you insist with some AO, check AN105 - Current Sense Circuit Collection from Linear

 

[dmta]

Hi everyone thank you for replying. I wanted to use this IC because it was from TI (free samples) and the fact that is through hole. Looks like I will have to go for a SMD chip.

Regards