INA 122 as current shunt monitor

Discussion in 'General Electronics Chat' started by dmta, Jun 15, 2013.

  1. dmta

    Thread Starter Member

    Mar 24, 2013
    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 !!!!!!!!!!!!!!!!
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    It wont as your diodes only drop the supply by 1.4V, so your current in the sense resistor R3 is 3.4Amps.

    You need to build the circuit on page 9, figure 6 of the datasheet.
  3. GopherT

    AAC Fanatic!

    Nov 23, 2012
    What do you expect it to do? What device(s) on your circuit board is the equivalent of I1 (current source)?

    Is the current source able to generate some type of function on your simulation?

    Also, you are missing the resistor between pins 1 and 8 that sets your gain.

    36 v is the ABSOLUTE MAXIMUM supply voltage. The simulated one will be ok but any transients on your real circuit board can render a real chip useless.
  4. dmta

    Thread Starter Member

    Mar 24, 2013
    Thank you to both of you.

    Dear Dodgydave and GopherT,

    This is to measure motor current draw in a brushed DC motor drive (H bridge) application. I wanted to use the high side configuration because from what I read (in the internet) people have said it to be not good (my knowledge in this matter is very limited).

    I will be using PWM frequencies not less than 10kHz. So I would like to ask is it ok to do the low side measurment?