PN junction diodes allow current to flow in one direction but not the other. When forward biased, the diode conducts fully and current flows. When reverse biased, the diode blocks current flow. Ideal diodes have no resistance and no voltage drop when forward biased, and infinite resistance when reverse biased. Diode characteristics include forward voltage drop, maximum current and power dissipation, and reverse breakdown voltage. Diodes are specified based on these operating limits and parameters.

1. PN junction diodes
Department of Electrical & Electronics Engineering, Amrita School of Engineering

2. PN Junction Diode
• Allows current to flow in one
direction but not the other
• The anode connects to the p-
type material, the cathode to
the n-type material of the
diode.
Department of Electrical & Electronics Engineering, Amrita School of Engineering

3. Forward Biased Diodes
• The component is biased so that the anode is more
positive than the cathode.
• The diode conducts fully when VF is approximately
0.7 V (for silicon) or 0.3 V (for germanium).
• The value of IF depends on the circuit voltage and
resistance values.
Department of Electrical & Electronics Engineering, Amrita School of Engineering

4. Reverse Biased Diodes
• The component is biased so that the cathode is more
positive than the anode.
• The voltage across the diode is approximately equal
to the applied voltage (V ).
• The diode current is approximately 0 A (as indicated
by the ammeter).
Department of Electrical & Electronics Engineering, Amrita School of Engineering

5. Ideal diode characteristics
• When reverse biased (open switch), the diode:
– Has infinite resistance.
– Blocks current.
– Drops the applied voltage across its terminals.
 When forward biased (closed switch), the diode:
 Has no resistance.
 Does not limit current.
 Has no voltage drop across its terminals.
Department of Electrical & Electronics Engineering, Amrita School of Engineering

6. Current through Ideal diode
I = 10 mA
Department of Electrical & Electronics Engineering, Amrita School of Engineering
I = 0 mA

7. Problem #1
1. Find the values of I and V in the circuits shown below.
Assume diodes to be ideal.
(a)
I = 2mA, V = 0V
Department of Electrical & Electronics Engineering, Amrita School of Engineering
(b)
I = 2mA, V = 0V

8. Characteristics of Junction diode
Forward-bias region
# Cut-in voltage - below
which, minimal current
flows
- approximately 0.5V
# Fully conducting
region – region where
Rdiode is approximately
equal zero
– between 0.6 and
0.8V
Diode current,
Department of Electrical & Electronics Engineering, Amrita School of Engineering

9. Characteristics of Junction diode
Reverse-bias region
# Saturation current-
constant current in
reverse direction
i = - Is
# Breakdown – when
VD << 0
Department of Electrical & Electronics Engineering, Amrita School of Engineering

10. Graphical Analysis Using Exponential Model
VDD  ID R VD
Department of Electrical & Electronics Engineering, Amrita School of Engineering
VD  VDD  IDR
• load line and diode
characteristic intersect
at operating point

11. Diode Temperature dependence
The reverse saturation
current Is will double in
magnitude for every 10°C
increase in temperature
Department of Electrical & Electronics Engineering, Amrita School of Engineering
The forward voltage drop
decrease by approx. 2 mV
for every 1°C increase in
temperature

12. Diode Specifications
Department of Electrical & Electronics Engineering, Amrita School of Engineering
• Forward voltage Vf
• Maximum forward current If
• Reverse saturation current
• Reverse voltage
• Peak Repetitive Reverse Voltage VRRM (or)
• Peak Inverse Voltage PIV
• Maximum power dissipation
• Capacitance levels
• Operating temperature range

13. Diode Specifications
• Peak Repetitive Reverse Voltage VRRM
 VRRM is the maximum reverse voltage that a diode can
withstand.
 When VR > VRRM , diode reverse current (IR) increases
rapidly as the depletion layer breaks down.
• Average Forward Current (IF ) – The maximum
allowable value of dc forward current for a diode.
• Forward Power Dissipation ( PD(max) ) – The maximum
possible power dissipation of the forward-biased diode.
F
Department of Electrical & Electronics Engineering, Amrita School of Engineering
F
V
I 
PD(max)

14. Diode Specification Sheets
Department of Electrical & Electronics Engineering, Amrita School of Engineering

15. Diode Specification Sheets
Department of Electrical & Electronics Engineering, Amrita School of Engineering

16. Diode Specification Sheets
Department of Electrical & Electronics Engineering, Amrita School of Engineering

17. Diode Specification Sheets
Department of Electrical & Electronics Engineering, Amrita School of Engineering

18. Diode Specification Sheets
Department of Electrical & Electronics Engineering, Amrita School of Engineering

19. Types of Diodes
Department of Electrical & Electronics Engineering, Amrita School of Engineering

20. Diode Testing
Department of Electrical & Electronics Engineering, Amrita School of Engineering

21. Diode Testing
Department of Electrical & Electronics Engineering, Amrita School of Engineering

22. Diode Testing
Department of Electrical & Electronics Engineering, Amrita School of Engineering

23. Diode Testing
Department of Electrical & Electronics Engineering, Amrita School of Engineering