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

 

[ericgibbs]

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

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.?

 

[dmta]

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 ?

 

[ericgibbs]

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.

 

[ChrisP58]

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.

 

[dmta]

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