op_amp_problem6 - Sample problems Topic Operational Amplifiers Statement of problem The opamps in the circuit are ideal 90k 120k 15k 5V ia 1k 5V 30k

Sample problems Topic: Operational Amplifiers Statement of problem The opamps in the circuit are ideal. - + - + a i 5 V − 5 V − 5 V 5 V 400 mV 30 k Ω 120 k Ω 1 k Ω 90 k Ω 15 k Ω 500 mV (a) Find a i . (b) Find the value of the right source voltage for which 0 a i = . Solution (a) The idea is to find out output voltages of the two opamps, and then to find out the current in between. The left opamp is virtually grounded, so the current flowing through the left source is 1 500 33.3 15 mV i A k μ − = = − Ω Then its output voltage is obtained using KVL 1 1 90 3 o v i k V = − × Ω = (1) Repeating the same process for the right source and opamp, its output voltage is obtained