Question

nsider the circult shown on the right. a) Which diodes are forward biased and which are reverse biased? b) Assume 0.7 V drop across each forward- D1 -5V biased diode and find Vo. +5V D2 Vo +5VD3 -5V D4 Two ideal diodes are placed in a circuit shown on the 2. D1 120 D2 60 Va right: a) Determine which diodes conduct and which R 18 5.4V 5V ones do not b) Assume D1 and D2 both conduct. Find Va and shown that your assumption was correct c) Would your answer depend on the value of R? d) What is the maximum value of R above which D2 opens? Determine and sketch vo (t) if vi (t) 15 sin(2n60t) V for the following circuit assuming the 3. diode is ideal.

Answer 1

a) ufor diode D., Voltage across d. +5-(-5) = lov 100)0.7v (Assunung cutting voltage 0.7] D, is forward biased & sig for diode D₂, Voltage across D2 = (+5)-(+5)= ov OV <0.7V so do is reverse biased. lig for diode Da, Voltage across D3 = (+5)-(+5)= OV OVLO.TV So, Iz is reverse biased. (iv) for diode Du, +5-(-5) = lov lov) 0.7V so, Dy is forward biased.

(6) As diode d, and Dy are forward- biased, replace them with shy circuit with 0.7 Voltage and replace Dz and Do by open cire +5V Ť +5voo P P T Vo= -5+ (670) Vo= – 4.3v Vo will be - 4.3 v.

for checking biasing condition, first find out voltage across diode if comes out to be greater than cuttin voltage it is forward biased ,otherwise it is reverse biased. By using this criterion,D₁ and D4 will be forward biased and D₂ AND D₃ are reverse biased.