# What will be the output voltage of an Op-amp inverting adder.

## What will be the output voltage of an Op-amp inverting adder for the input voltages V1=-10V, V2=+10V, V3= +5V and resistances R1= 600K Ω , R2= 3000K Ω & R3= 2M Ω if the feedback resistance is considered to be 2M Ω ?

a. -38.3V

b. 38.3V

c. 40V

d. -40 V

Correct Answer : a. -38.3V

**Explanation :**

Given data:

V1= -10V, R1= 600k

V2= 10V, R2= 300K

V3= 5V, R3= Rf=2M

The output voltage of an inverting adder or summer circuit is evaluated by,

V_{o}= -(K_{1}V_{1} + K_{2}V_{2} + K_{3}V_{3})

where, 'K' represents the constant gain factor.

K_{1}= R_{f}/ R_{1} = 2M/ 600K= 2000K/ 600K = 3.33

K_{2} = Rf / R2 = 2M/300K = 2000K/ 300K = 6.66

K_{3} = R_{f} / R_{3} = 2M/ 2M = 1

Therefore, V_{o} = -(K_{1}V_{1} + K_{2}V_{2} + K_{3}V_{3})

= -[ 3.33 x (-10) + 6.66 x (10) + 1 x 5]

= - [ -33.3 + 66.6+ 5]

= -38.3 V

Hence, the final output value of voltage of an inverting amplifier is nothing but summation of all input voltages estimated to be in terms of negative voltage of about -38.3 V.