Question

Determine the current through the diode, when the switch is in position 1, 2& 3. Assuming op-amps initially nulled.

(a) Io (LED) =4.01mA; Io (Zener) =4.01mA; Io (rectifier) =8.33mA

(b) Io (LED) =25mA; Io (Zener) =4.01mA; Io (rectifier) =4.01mA

(c) Io (LED) =16.67mA; Io (Zener) =16.66mA; Io (rectifier) =4.01mA

(d) Io (LED) =8.33mA; Io (Zener) =8.33mA; Io (rectifier) =8.33mA

The question was asked in an internship interview.

Question is from Voltage to Current Converter with Floating and Grounded Load topic in section Operational Amplifier Applications of Linear Integrated Circuits

Answer 1

The accurate choice is (d) Io (LED) =8.33mA; Io (Zener) =8.33mA; Io (rectifier) =8.33mA

Let me simplify it: All the diodes are connected one after another in the feedback path. Therefore, current through the diode remains same. Io =Vin/R1 =1.5/180 =8.33mA.