INA 122 as current shunt monitor

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 !!!!!!!!!!!!!!!!

dmta said:

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 !!!!!!!!!!!!!!!!

Click to expand...

hi,
One point is you have no Rg resistor on pins #1 and #8.

E.

EDIT:
do you have more details of the shunt reg?.
what is limiting the current to 0.5A.?

Hi ericgibbs thank you for the reply.

According to the IC schematic given in the datasheet this should work fine without a Rg resistor. But anyway I put a 200k (which gives a gain of 6) and simulated in multisim. Still it is not the right O/P.

BTW when I do this it works


The data sheet says "Signal Input Terminals, Voltage(2) ....................... (V–)–0.3V to (V+)+0.3V" Does this mean that the inverting and non inverting inputs can go upto 35.9V in my case ?

hi,
The input range should be OK.

Check page #7 of the datasheet for the value of RG. A value of 200K is far too high.

TI makes a dedicated current shunt monitor amps. I am using an INA195 for a project right now. It has a common mode range from -16 to +80V, regardless of the operating voltage.

I'm running it at +5V power, but measuring the current through a resistor at +14Volts.

Thank yoy chris !!!!!

I would love to use something like that but since it is a SMD device I didn't like it. But it is high time to move into SMT I guess !!!!!!!!!!!!!!