# Op amp calculation

Assuming that the op amp and the diode are ideal (for op amp: infinite input impedance and 0 output impedance, for diode: 0 voltage drop):

D1 is open <=> $$V_i \frac{R2}{R1}>E$$

• case 1 (D1 closed):

$$V_i < E\frac{R1}{R2}$$

$$V_o = -V_i \frac{R2}{R1}$$ (It's a simple inverter)

• case 2 (D1 open):

$$V_i > E \frac{R1}{R2}$$

$$Vo = -V_i \frac{R2||R3}{R1} -E \frac{R2||R3}{R3}$$

How do you get the last relation (case2, Vo=...) ?

where $$R1||R2 = \frac{R1 \cdot R2}{R1+R2}$$

• Gotta love those "ideal" 741 opamps. Jan 30 '13 at 18:12
• Those "ideal" diodes are pretty sweet, too. Jan 30 '13 at 18:29
• They are limited edition... Jan 30 '13 at 20:07

## 1 Answer

Is this homework problem from your superposition chapter? Short E, solve for Vo in terms of Vin. Short Vin, solve for Vo in terms of E. The final answer you have there could be simplified..