Answer to Question #205762 in Electrical Engineering for Pavithra

Question

Design a circuit find the sum of 2 input voltages V1 and V2 op-amp may be used in inverting mode

Answer 1

Employing the circuit below to get $V_{out}=-K_1*V_1+K_2*V_2$ for a reasonable gains with positive values of K₁ and K₂ .

$V_{out}=-V_1(\frac{R_3}{R_1})+V_2(\frac{R_4}{R_2+R_4})(\frac{R_1+R_3}{R_1})$

Assuming K₁=1 and K₂=2 are your requirements, define R₁=R₃ with a suitable value.

With this limitation, you must construct K₂ with R₂=0, thus link V₂ straight to the (+) input, rendering R₄ obsolete and allowing R₄ to be deleted.

In a nutshell, the answer is to connect V₂ to the (+) input terminal directly and set R₁=R₃.

In reality, this circuit is frequently used with R₁=R₂ and R₃=R₄ to provide a balanced subtractor with gain R₃/R₁=R₄/R₃ in each input, i.e., Vout=(R₃/R₁)* (V₂-V₁).