1. Diodes
Pictures are redrawn (with some modifications) from Introductory Electronic Devices and Circuits By
Robert T. Paynter

2. Objectives Identify the terminals of a pn-junction diode.
List and describe the three diode models.
List main parameters of the pn-junction diode.
Discuss the basic operating principles of the zener diode.
List main zener diode parameters.
Discuss the basic operating principles of light-emitting diode (LED).

3. Fig 2.1 PN-junction diode schematic symbol.
Anode
Cathode p n

4. Fig 2.2 Forward-biased diodes.

5. Fig 2.3 Reverse-biased diodes.

6. Table 2.1 Diode Model Summary.
Applications
Ideal
Circuit troubleshooting
Practical
Mathematical circuit analysis
Determining suitability of a diode for a given application
Complete
Circuit development (engineering)
Special-case circuit analysis
Explaining differences between predicted and measured circuit values

7. Fig 2.4 Characteristics of ideal diode.

8. Fig 2.5 Example 2.1.

9. Fig 2.6 Example 2.2.

10. Fig 2.7 Ideal diode characteristics.
Forward bias
Reverse Bias
Biasing polarities
Equivalent switch state ON
OFF
Device resistance
Zero
Infinite
Device current
A-to-K current determined by external resistance and voltage
A-to-K voltage
Equal to the applied voltage
(+)
(-)
(-)
(+) IF

11. Fig 2.8 Diode characteristic curves.

12. Fig 2.9 Effect of VF. Value Ideal Practical VF 0 V 0.7 V VR1 5 V 4.3 V
5 mA
4.3 mA

13. Fig 2.10 Example 2.3 & 2.4.

14. Percentage of Error where X = the measured value
X’ = the calculated value
From Fig. 2.9,

15. Fig 2.11 Example 2.5.

16. Fig 2.12 Example 2.6.

17. Fig 2.13 Example 2.7.

18. Fig 2.14 Peak reverse voltage (VRRM).

19. Fig 2.15 Applying AC voltage to a diode circuit.

20. Fig 2.16 Example 2.8. Diode part number Peak reverse voltage 1N4001 50
100
1N4003
200
1N4004
400
1N4005
600
1N4006
800
1N4007
1000

21. Fig 2.17 Example 2.9 (average forward current I0).
Choose a diode with average forward current I0 at least 20% greater than the actual average current.

22. Fig 2.18 Example 2.10 (Forward Power Dissipation PD(max)).
Choose a diode with forward power dissipation PD(max) at least 20% greater than actual power dissipation.

23. I0 and PD(max) relationship
where I0 = the limit on the average forward current
PD(max) = the forward power dissipation rating of the diode
VF = the diode forward voltage (0.7V for Si)

24. Example 2.11.
A diode has a forward power dissipation rating of 500 mW. What is the maximum allowable value of forward current for the device?

25. Fig 2.19 Complete-model diode curve.
Forward operating region
Reverse operating region (also called the reverse breakdown region)

26. Example 2.12.
Determine voltage across diode in Fig for the values of IF = 1 mA and IF = 5 mA. Assume that the value for RB = 5 W.
IF = 1 mA:
IF = 5 mA:
Bulk resistance has a significant effect on voltage drop across diode terminals when the forward current is large.

27. Diode Equation (Accurate Model)
where
where
The equation is not valid in the reverse breakdown region.

28. Reverse Current
Diode reverse current (IR) consists of two parts: saturation current (IS) and surface leakage current (ISL).

29. Fig 2.21 Effect of reverse current.

30. Fig 2.22 Diode capacitance.

31. Fig 2.23-24 Temperature effects on diode operation.

32. Fig 2.25 The 1N400X series specifications.
See “1N400X.pdf”
Current rating (I0) of 1N400X is 1 A. For rating of 3 A, use 1N540X instead.

33. Table 2.2 Diode Maximum ratings.
Discussion
Peak repetitve reverse voltage, VRRM
Maximum allowable reverse voltage.
Nonrepetitive peak reverse voltage, VRSM
Maximum allowable value of a single event reverse voltage. (VRSM > VRRM)
RMS reverse voltage, VR(rms)
VR(rms) = VRRM
Average rectified forward current, I0
Maximum average diode current.
Nonrepetitive peak surge current, IFSM
Maximum allowable value of forward current surge. (30A for 1N400X)
Operating and storage junction temperature, TJ or Tstg
Temperature that diode can withstand.

34. Fig 2.26 Diode packages.

35. Table 2.3 Diode electrical characteristics.
Maximum forward voltage drop, VF
Maximum value that VF will ever reach.
Maximum full-cycle average forward voltage drop, VF(AV)
Maximum average forward voltage.
Maximum reverse current, IR
Usually given at various temperature. The rating is valid for all reverse dc voltage below VRRM.
Maximum full-cycle average reverse current, IR(AV)
Maximum average value of IR.

36. Fig 2.27 Diode selection guide.
See handout.

37. Fig 2.28-30 Zener characteristics.

38. Fig 2.31 Determining Zener impedance.

39. Fig 2.32 Zener equivalent circuits.
Ideal: ZZ = 0
Prac.: ZZ > 0

40. Example 2.13 Zener diode.
A 1N754A Zener diode has a dc power dissipation rating of 500 mW and a nominal Zener voltage of 6.8 V. What is the value of IZM for the device?

41. Fig 2.33 Specification of 1N4370A series (Zener diodes).
See “1N4370A Series.pdf”

42. Fig 2.34 Zener selector guide.
See handout.

43. Fig 2.35-37 Light emitting diodes.
LED symbol

44. Table 2.4 Common LEDs. Elements Forward voltage (VF) Color Emitted
GaAs
1.5 IF = 20 mA
Infrared (invisible)
AlGaAs
1.8 IF = 20 mA
Red
GaP
2.4 IF = 20 mA
Green
AlGaInP
2.0 IF = 20 mA
Amber (yellow)
AlGaInN
3.6 IF = 20 mA
Blue

45. Fig 2.38 A LED needs a current-limiting resistor.

46. Fig 2.39 Multicolor LED.

47. Fig 2.40-42 Diode testing. Forward bias Reverse bias
This button is for diode testing.
Reverse bias

48. Fig 2.43 Common diodes. Rectifier Zener LED Schematic symbol
Bias for normal operation
Switched back and forth between forward and reverse.
Reverse
Forward
Normal VF
Si: VF = 0.7 V
Ge: VF = 0.3 V
VF = 0.7 V (not normally operated)
Normal VR
Equal to applied voltage.
Equal to VZ.
Primary factors to consider for device substitution
I0 and VRRM ratings.
PD(max) and VZ ratings.
VF(min), IF(max), and VBR

49. DC Load Line
Load line eq.:

50. Summary PN-junction diodes. Three diode models. Diode specifications.
Zener diodes.
Zener circuits.
Light-emitting diodes (LED).