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INA126, single power, differential ampifier problem.

James F.R Mars
Prodigy 10 points

Other Parts Discussed in Thread: INA126, INA213

Hello, 

I want to measure the current of Rsense. 

Rsense = 0.01 ohm, 

Vin+ (max) = 7~8V (when Ic =0), Vin+(min)= 2~3V (when Ic = max)

Vin- (max)= around(Vin+(max)- 0.0001V) (when Ic=0), Vin- (min) = around(Vin+(min) -0.015V) (when Ic=max)

I want to amplitude the voltage difference between Rsense and get a voltage range 0~5V for ADC from output of INA126. 

In the circuit above, I use single power, DC12V, I think it doesn't need the dual power.

My concept is that G=30, so Rg=3200 ohm.

I expected that result of Graph-2, but the result of measurement was Graph-3. ??? why?

When Ic=0, Vin+=7.5V, Vin-=7.44449V, --> Vo= 7.xxx V

When Ic=max, ---> Vo=2.25V around , ??? --> Graph-3.

Is there a problem in the circuit? 

Does it need a series resistor for Vin+ and Vin-, respectively, for current limit?

I need your help..

Thanks.

  • 0
    TI__Mastermind 25875 points

    Hello James,

    Please consider a current shunt monitor for this application.

    With instrumentation amplifier, output swing changes with common-mode voltage (see figures at bottom of page 4 in INA126 data sheet).

    Current shunt monitor output swing does not change with common-mode voltage.

    Please consider INA213. Gain is fixed at 50V/V, so decrease your shunt resistor accordingly.

    For power supply you can use 5V. It is better to interface with ADC since output of INA213 cannot exceed 5V.