Switching characteristics, diode capacitances

3. R.M.K COLLEGE OF ENGINEERING
AND TECHNOLOGY
DEPARTMENT OF ECE
EC8252-ELECTRONIC DEVICES
SECOND SEMESTER-I YEAR- (2020-2024 BATCH)
Mrs. P.Sivalakshmi AP/ECE
SESSION:10
DATE: 28.04.2021

4. Next session:
Transition & Diffusion capacitance
Switching Characteristics
Breakdown in PN Junction Diodes
Problems

5. Diode Switching Characteristics

6. DIODE SWITCHING TIMES
While changing the bias conditions, the diode
undergoes a transient response. The response of a
system to any sudden change from an equilibrium
position is called as transient response.
The sudden change from forward to reverse
and from reverse to forward bias, affects the circuit.
The time taken to respond to such sudden changes is
the important criterion to define the effectiveness of
an electrical switch.

7. The time taken before the diode recovers its
steady state is called as Recovery Time.
The time interval taken by the diode to switch
from reverse biased state to forward biased
state is called as Forward Recovery Time.
The time interval taken by the diode to switch
from forward biased state to reverse biased
state is called as Reverse Recovery Time.

8. Under Forward Bias
The majority carriers in P-type holes = Ppo
The majority carriers in N-type electrons =
Nno
The minority carriers in P-type electrons =
Open Circuited
Equilibrium
Minority carrier
concentration

9. Under Reverse Bias

10. Steady state at forward bias Steady state at reverse bias
Recovery time
Removing excess
minority carriers
near junction

12. Reverse Recovery Time

16. FACTORS THAT AFFECT DIODE SWITCHING TIMES
• Diode Capacitance − The PN junction capacitance
changes depending upon the bias conditions.
• Diode Resistance − The resistance offered by the
diode to change its state.
• Doping Concentration − The level of doping of the
diode, affects the diode switching times.
• Depletion Width − The narrower the width of the
depletion layer, the faster the switching will be. A
Zener diode has narrow depletion region than an
avalanche diode, which makes the former a better
switch.

17. APPLICATIONS
There are many applications in which
diode switching circuits are used,
such as
High speed rectifying circuits
High speed switching circuits
RF receivers
General purpose applications
Consumer applications
Automotive applications
Telecom applications etc

18. DIODE JUNCTION CAPACITANCE
In a p-n junction diode, two types of capacitance take place. They are,
1.TRANSISTION CAPACITANCE (CT) CT = dQ / dV
CT = ε A / W

19. 2.Diffusion capacitance (CD)
Forward bias of Transition capacitance
The formula for diffusion capacitance is CD
= dQ / dV ,