diode switching times
TRANSCRIPT
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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