[Single chip notes] practical circuit for op amp current detection

1. Low-end op amp current detection method:

Analyze the principle:

Using the virtual short characteristics of the op amp , we get:

V ₊ = V- _；

Using the virtual-off characteristic of the op amp , there is no current flowing through the input and output. So the currents flowing through R3 _and R6 are _equal .

(V_OUT-V_-)/R₃ = V_-/R₆；

From the above two equations, we can get

V_OUT = V₊ * (R₃ + R₆)/R₆；

And there is:

V ₊  = I * R ₈ ；

So have:

I =V₊ / R₈ = V_OUT * R₆/(R₃ + R₆)/R₈；

The current is converted in this way, the resistance of several resistors is adjusted, and V _out can be sampled by the ADC of the microcontroller.

2. High-end current detection circuit

The ultimate purpose of this circuit to detect the current is to obtain the relationship between V _OUT and V ₁ and V ₂ on the figure .

Let's analyze the input first, the virtual break can be seen:

V ₊ /R ₇  = （V ₂ -V ₊ ) / R ₅；

Imaginary short gets:

V ₊ = V- _；

The current of one path of the input negative is equal:

（V_--V_OUT)/R₁ = （V1-V-)/R₂；

Usually when using this circuit there are R ₁  = R ₇ , R ₂  = R ₅ .

The above formula includes:

V_OUT = (V₂-V₁)*R₁/R₂；

V₂-V₁ = I*R₄;

so 

I = V_OUT*R₂/(R₁*R₄) ;

The above is to record and share the content.

By Urien February 26, 2018 11:00:07