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ALPHA BREATHING

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Diode switching times

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Diode switching times

Input waveform &Diode circuit

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Forward Recovery Time

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Diode Switching time

a) Till t1, diode forward biased ,forward voltage VFis applied. RLis high,drop in RL> drop in diode. current IF= VF/RL, neglect diode R

b) At t1,voltage is reversed (-VR).No of minority carriers take to reduce frompn-pn0to zero . due to this at t1current reverses and remains at that reverse

value

IRtill the minority carrier concentration reduces to 0.current is

IR=VR/R till t2.

c) From t2on wards, diode voltage starts to reverse and diode current starts

to decrease. at t=t3diode state completely gets reversed and attain steadystate in reverse bias condition.

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Storage Time(ts)

During time t1to t2, the minority charge carriers remain stored and decrease

slowly to zero.

Transition Time(tt)The time from t2to t3,time required by the diode current to reduce to its

reverse saturation value.

Reverse Recovery Time(trr)

The total time required by the diode which is the sum of tsand ttto recover

completely from the change of state.

trr=ts+tt

trr depends on RC time constant ,where Ctransition capacitance of diode

Total switching time trr limits on the maximum operating frequency of the

diode.

To minimize the effect of reverse current, the time period of the operating

frequency must be at least 10 times trr

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Example

Calculate the maximum operating frequency of a diode

whose reverse recovery time is 9ns.

Solution

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Puzzles

Ram gets 148 marks for 20 questions.

The pattern is he get 10 marks for the right

answer and3 marks for the wrong answer.

Can you guess how many of his answers were

correct?

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SUMMARY

Diode switching times

Introduction

Characteristics Transition time

Storage time

Reverse recovery time Diode resistance

Definition , V-I characteristics, Dynamic

resistance