Electrical – Transient analysis of op-amp circuit

operational-amplifiertransient

What is the expression of V if V(0) = 4V?

schematic

simulate this circuit – Schematic created using CircuitLab

I am unable to proceed further after forming the following equation:
-v/R1=(v-V)/R2+C1dv/dt

Best Answer

Let the op amp output voltage be \$v_o\$

At the inverting input, \$v^-=0\$ since it's a virtual earth.

Therefore, KCL at the \$ v^-\$ node gives:

$$ C\frac{dv_o}{dt}+\frac{v_o}{R_2}=0$$ or $$ \frac{dv_o}{dt}+\frac{v_o}{R_2C}=0$$

Solving this ODE:

$$ v_o=Ae^{-t/R_2C}$$

Initial condition: $$ t=0,\: v_o=4$$

Hence \$A=4\$, and:

$$ v_o=4e^{-t/R_2C}=4e^{-2t}$$