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

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Presentation on theme: "Diode Diode is the simplest semiconductor device. It’s a two-terminal device."— Presentation transcript:

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
- 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
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

18 Diode specification sheets

19 Other types of diodes Zener diode Light emitting diode (LED) Diode arrays

20 Zener diode

21 Light emitting diode (LED)

22 Diode arrays

23 Diode equivalent circuits
Piecewise linear model Simplified model Ideal device

24 Piecewise linear model

25 Simplified model

26 Ideal device

27

28

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

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

31 Load-line analysis

32 Example: Simple diode circuit

33 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 (e) Repeat (a) using the ideal diode model. (f) Repeat (b) using the ideal diode model.

34 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

35 Example: (b) E = 10 Volts, R = 2 kOhms
Y-intercept = E/R = 5 mA Slope = -1/ R = 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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