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Diode is the simplest semiconductor device. It’s a two-terminal device

Diode. Diode is the simplest semiconductor device. It’s a two-terminal device. Basic operation. Ideal diode conducts current in only one direction and acts like open in the opposite direction. Characteristics of an ideal diode: Conduction region. Conduction region

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Diode is the simplest semiconductor device. It’s a two-terminal device

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  1. Diode Diode is the simplest semiconductor device. It’s a two-terminal device

  2. Basic operation Ideal diode conducts current in only one direction and acts like open in the opposite direction

  3. Characteristics of an ideal diode: Conduction region Conduction region - the voltage across the diode is zero - the current near infinite - the diode acts like short

  4. Characteristics of an ideal diode: Non-conduction region Www.cpe.kmutt.ac.th/~sanan Non-conduction region - all of the voltages is across the diode - the current is zero - the diode acts like open

  5. Semiconductor materials Two types of materials used in development of semiconductor are Silicon(Si) and Germanium(Ge) Doping is a process to add impurity(such as Antimony(Sb) or Boron(B)) to Si or Ge to make two types of semiconductor materials: n- type material: make Si(or Ge) more negative (has “free” electrons) p- type material: make Si(or Ge) more positive (has “holes”) Joining n-type and p-type materials makes a p-n junction diode

  6. P-n junction diode “electrons” in n-types material migrate across the junction to p-type material and forms a so-called “depletion region” around the junction.

  7. No bias condition

  8. Reverse bias condition

  9. Forward bias condition

  10. Actual diode characteristics

  11. Zener region

  12. Resistance levels • DC or Static resistance • AC or Dynamic resistance • Average AC resistance

  13. DC or Static resistance

  14. AC or Dynamic resistance Forward bias region: • The resistance depends on the amount of current(ID) in the diode. • The voltage across the diode is fairly constant(26 mA for 25 C). • rB ranges from a typical 0.1 Ohms for high power device to 2 Ohms for low power, general purpose diodes. Reverse bias region: • The resistance is infinite. The diode acts like an open.

  15. AC or Dynamic resistance(cont’d)

  16. Average AC resistance

  17. Diode specification sheets

  18. Other types of diodes • Zener diode • Light emitting diode (LED) • Diode arrays

  19. Zener diode

  20. Light emitting diode (LED)

  21. Diode arrays

  22. Diode equivalent circuits • Piecewise linear model • Simplified model • Ideal device

  23. Piecewise linear model

  24. Simplified model

  25. Ideal device

  26. Determine VDQ, IDQ and VR if (a) E = 20 V, R = 1 kOhms (b) E = 10 V, R =10 kOhms

  27. (a) E=20V, R = 1k: E = VD + VR = VD + RID Try VD = 0.5 = 19.5 mA = 19.5/1000 ID = (E - VD)/R From the graph, at ID = 19.5 mA, VD = 0.9 V Try VD = 0.9 = 19.1 mA = 19.1/1000 ID = (E - VD)/R Therefore, ID = 19.1 mA, VD = 0.9, VR = 19.1 V (b) E=10V, R = 10k: Try VD = 0.5 = 0.95 mA = 9.5/10000 ID = (E - VD)/R From the graph, at ID = 0.95 mA, VD = 0.55 V Try VD = 0.55 = 0.94 mA = 9.45/10000 ID = (E - VD)/R Therefore, ID = 0.94 mA, VD = 0.55, VR = 9.45 V

  28. Load-line analysis

  29. Example: Simple diode circuit

  30. Example: Simple diode circuit Find VDQ, IDQ, and VR if (a) E = 10 Volts, R = 1 kOhms (b) E = 10 Volts, R = 2 kOhms (c) Repeat (a) using the approximate equivalent model for the Si diode. (d) Repeat (b) using the approximate equivalent model for the Si diode. (e) Repeat (a) using the ideal diode model. (f) Repeat (b) using the ideal diode model.

  31. Example: (a) E = 10 Volts, R = 1 kOhms Y-intercept = E/R = 10 mA Slope = -1/ R = 1 mA/V From the load-line: IDQ = 9.15 mA VDQ = 0.82 V VR = IDQ x R = 9.15 V

  32. Example: (b) E = 10 Volts, R = 2 kOhms Y-intercept = E/R = 5 mA Slope = -1/ R = 0.5 mA/V From the load-line: IDQ = 4.6 mA VDQ = 0.78 V VR = IDQ x R = 9.2 V

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