1. PN-Junction Diode Characteristics
Forward Bias --- External battery makes the Anode more positive than the Cathode --- Current flows in the direction of the arrow in the symbol.
Reverse Bias --- External battery makes the Cathode more positive than the Anode --- A tiny current flows opposite to the arrow in the symbol.

2. Graphical PN-Junction Diode V-I Characteristic
Forward Bias Region
Reverse Bias Region
Reverse breakdown

3. Mathematical Approximation

4. Ideal PN Junction Diode V-I Characteristic
Forward Bias – Short Circuit
Reverse Bias – Open Circuit

5. Diode Reverse Recovery Time
ta is the time to remove the charge stored in the depletion region of the junction
tb is the time to remove the charge stored in the bulk semiconductor material

6. Reverse Recovery Characteristics Soft Recovery
Reverse recovery time = trr = ta+tb
Peak Reverse Current = IRR = ta(di/dt)

7. Reverse Recovery Characteristics Abrupt Recovery
Reverse recovery time = trr = ta+tb
Peak Reverse Current = IRR = ta(di/dt)

8. Series-Connected Diodes
Use 2 diodes in series to withstand higher reverse breakdown voltage.
Both diodes conduct the same reverse saturation current, Is.

9. Diode Characteristics
Due to differences between devices, each diode has a different voltage across it.
Would like to “Equalize” the voltages.

10. Series-Connected Diodes with Voltage Sharing Resistors

11. Series-Connected Diodes with Voltage Sharing Resistors

12. Series-Connected Diodes with Voltage Sharing Resistors
Is = Is1+IR1 = Is2+IR2
IR1 = VD1/R1
IR2 = VD2/R2 = VD1/R2
Is1+VD1/R1 = IS2+VD1/R2
Let R = R1 = R2
Is1 + VD1/R = Is2 +VD2/R
VD1 + VD2 = Vs

13. Example 2.3 Is1 = 30mA, Is2 = 35mA VD = 5kV
(a) – R1=R2=R=100kΩ, find VD1 and VD2
(b) – Find R1 and R2 for VD1=VD2=VD/2

14. Example 2.3 (a)

15. Example 2.3 (a) simulation

16. Example 2.3 (b)

17. Example 2.3 (b) simulation