Question Details

Consider the circuit shown. Assume that the diode (D) is ideal. Given vs = 100sin(2π50t) V, Vdc = 50 V, and R = 10Ω, the average value of the current through the diode is A (Round off to two decimal places)


Options

A

1.09

B

5.21

C

1.5

D

0.44

Show Answer

Correct Answer :

Option A

1.09

Solution :

The correct option is 1.09.

Let us analyze the given circuit shown in the image. The circuit consists of an AC voltage source, an ideal diode, a resistor, and a DC voltage source connected in series. The parameters are:
AC voltage source: vs(t)=100sin(ωt) V where the frequency is f=50 Hz and ω=2πf.
DC voltage source: Vdc=50 V
Resistor: R=10Ω

Since the diode is ideal, it acts as a short circuit (ON state) when it is forward-biased and an open circuit (OFF state) when it is reverse-biased. The diode starts conducting when the AC source voltage vs(t) exceeds the DC voltage source Vdc:
vs(t)>Vdc
100sin(ωt)>50
sin(ωt)>0.5

This condition defines the conduction angle of the diode. Within the first cycle [0,2π], the diode conducts between the angles θ1 and θ2:
θ1=sin-1(0.5)=π6 rad=30°
θ2=π-θ1=5π6 rad=150°

When the diode is conducting, the current i(t) through the diode is given by applying Kirchhoff's Voltage Law (KVL) around the loop:
i(t)=vs(t)-VdcR=100sin(ωt)-5010=10sin(ωt)-5 A

When the diode is not conducting, the current is zero:
i(t)=0 for all other values of ωt in the period [0,2π].

The average value of the current through the diode over one complete cycle is:
Iavg=12πθ1θ2i(θ)dθ
Iavg=12ππ/65π/6(10sinθ-5)dθ

Evaluating the definite integral:
π/65π/6(10sinθ-5)dθ=[-10cosθ-5θ]π/65π/6
=(-10cos5π6-55π6)-(-10cosπ6-5π6)
Since cos(5π/6)=-32 and cos(π/6)=32:
=(1032-25π6)-(-1032-π6)
=103-20π6=103-10π3

Substituting the numerical values 31.73205 and π3.14159:
103-10π317.3205-10.4720=6.8485

Now, compute the average current Iavg:
Iavg=6.84852π6.84856.2831851.09 A

Thus, the average value of the current through the diode is 1.09 A.

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