Diodes Zener diodes. Electronics Diodes. Terry Sturtevant. Wilfrid Laurier University. September 9, 2015

Transcription

1 Electronics Diodes Wilfrid Laurier University September 9, 2015

2 Diode an electronic device which passes current in one direction only

3 Diode an electronic device which passes current in one direction only diode starts to allow current in the forward direction when the voltage reaches around 0.6V

4 Diode an electronic device which passes current in one direction only diode starts to allow current in the forward direction when the voltage reaches around 0.6V If the voltage gets high enough in the reverse direction, the diode will conduct; reverse breakdown voltage

5 Negative pressure; no flow possible

6 No pressure; resistance to flow is large

7 Small pressure; resistance to flow decreases

8 Medium pressure; resistance to flow still decreasing

9 High pressure; resistance to flow small

10 Very high pressure; resistance almost zero

11 + - Diode symbol and physical appearance

12 anode + - Diode symbol and physical appearance

13 anode cathode + - Diode symbol and physical appearance

14 Signal diodes (one type)

15 Signal diodes (another type)

16 Diodes Power diodes (one type)

17 Diodes Power diodes (another type)

18 off off V 0.7 I small; changes slowly

19 off on V 0.7 I large; almost independent of V

20 V < V z reverse breakdown forward bias I small; changes slowly

21 reverse breakdown forward bias V z I large; almost independent of V

22 V s V D 0.7 V o V s 0.7 (assuming V s 0.7) Forward biased diode in a voltage divider

23 V s V o 0.7 (assuming V s 0.7) V D 0.7 Forward biased diode in a voltage divider

24 V s V o V s (assuming V s > 0) I 0 Reverse biased diode in a voltage divider

25 V s I 0 V o 0 (assuming V s > 0) Reverse biased diode in a voltage divider

26 One common use of diodes is for rectification, by putting diodes in a bridge circuit.

27 Here s the basic bridge.

28 - + B A The output is taken between A and B.

29 + - + B A - For one half of the cycle, these two diodes shown in green are forward biased, so they re on. (The others are off.)

30 - - + B A + For the other half of the cycle, the other two diodes shown in green are forward biased, so they re on. (The others are off.)

31 For both parts of the cycle, A is positive relative to B.

32 are a special case; they light up above a certain voltage. The voltage depends on the colour.

33 anode (+) cathode (-) The LED lights up when current flows from the anode to the cathode..

34

35 You must use a resistor to limit the current.

36 You must use a resistor to limit the current. Without a resistor, the LED will probably be destroyed.

37 The resistor can go before or after the LED.

38 The resistor can go before or after the LED.

39 Reverse-biased, the LED won t light up.

40 Reverse-biased, the LED won t light up.

41 Parameters One of the ways to produce a stable reference voltage, such as for an ADC or a DAC, is to use a Zener diode.

42 Parameters One of the ways to produce a stable reference voltage, such as for an ADC or a DAC, is to use a Zener diode.

43 Parameters One of the ways to produce a stable reference voltage, such as for an ADC or a DAC, is to use a Zener diode. V in

44 Parameters One of the ways to produce a stable reference voltage, such as for an ADC or a DAC, is to use a Zener diode. V in V out

45 Parameters One of the ways to produce a stable reference voltage, such as for an ADC or a DAC, is to use a Zener diode. V in R V out

46 Parameters One of the ways to produce a stable reference voltage, such as for an ADC or a DAC, is to use a Zener diode. V in R V out

47 Parameters Parameters

48 Parameters Parameters Zener voltage

49 Parameters Parameters Zener voltage required current

50 Parameters Parameters Zener voltage required current temperature sensitivity

51 Parameters Parameters Zener voltage required current temperature sensitivity variation with current (ac resistance)