Capacitors Diodes Transistors. PC200 Lectures. Terry Sturtevant. Wilfrid Laurier University. June 4, 2009

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1 Wilfrid Laurier University June 4, 2009

2 Capacitor an electronic device which consists of two conductive plates separated by an insulator

3 Capacitor an electronic device which consists of two conductive plates separated by an insulator value, capacitance, is proportional to the surface area of the plates and inversely proportional to the distance between the plates

4 Capacitor an electronic device which consists of two conductive plates separated by an insulator value, capacitance, is proportional to the surface area of the plates and inversely proportional to the distance between the plates measured in Farads

5 Capacitor an electronic device which consists of two conductive plates separated by an insulator value, capacitance, is proportional to the surface area of the plates and inversely proportional to the distance between the plates measured in Farads Farads are big

6 Capacitor an electronic device which consists of two conductive plates separated by an insulator value, capacitance, is proportional to the surface area of the plates and inversely proportional to the distance between the plates measured in Farads Farads are big usually microfarad (µf) or picofarad (pf) values are used

7 Capacitor uncharged

8 Capacitor charging; charge on opposite plates is equal and opposite.

9 Capacitor charging; charge on opposite plates is equal and opposite.

10 Capacitor charged; no more change

11 purpose is to store electrical charge.

12 purpose is to store electrical charge. current starts large, voltage starts at zero

13 purpose is to store electrical charge. current starts large, voltage starts at zero as charge is stored, voltage increases and current decreases until the voltage equals the applied voltage, when current becomes zero

14 A capacitor s voltage may not exceed the maximum for which it is rated. Big capacitors often have low maximum voltages.

15 A capacitor s voltage may not exceed the maximum for which it is rated. Big capacitors often have low maximum voltages. Capacitors may retain charge long after power is removed.

16 A capacitor s voltage may not exceed the maximum for which it is rated. Big capacitors often have low maximum voltages. Capacitors may retain charge long after power is removed. For safety, large capacitors should be discharged before handling.

17 A capacitor s voltage may not exceed the maximum for which it is rated. Big capacitors often have low maximum voltages. Capacitors may retain charge long after power is removed. For safety, large capacitors should be discharged before handling. Place 1kΩ 1kΩ resistor across the terminals to discharge.

18 A capacitor s voltage may not exceed the maximum for which it is rated. Big capacitors often have low maximum voltages. Capacitors may retain charge long after power is removed. For safety, large capacitors should be discharged before handling. Place 1kΩ 1kΩ resistor across the terminals to discharge. High voltage capacitors should be stored with terminals shorted.

19 I = 0 R Q = 0 V c = 0 V s t = 0, switch open

20 I = V s /R R Q = 0 V c = 0 V s t = 0, switch closed

21 I < V s /R R Q > 0 V s > V c > 0 V s t RC

22 I = 0 R Q = CV s V c = V s V s t >> RC

23 Some capacitiors are unpolarized (like resistors);

24 Some capacitiors are unpolarized (like resistors); i.e. they can be placed either way in a circuit.

25 Some capacitiors are unpolarized (like resistors); i.e. they can be placed either way in a circuit. Other types, (such as electrolytics ), must be placed in a particular direction

26 Some capacitiors are unpolarized (like resistors); i.e. they can be placed either way in a circuit. Other types, (such as electrolytics ), must be placed in a particular direction (indicated by a + sign at one end.)

27 Some capacitiors are unpolarized (like resistors); i.e. they can be placed either way in a circuit. Other types, (such as electrolytics ), must be placed in a particular direction (indicated by a + sign at one end.) Big capacitors ( 1µF ) are usually electrolytic.

28 Non-polarized capacitor

29 Polarized capacitor connected the right way

30 Polarized capacitor connected the wrong way

31 Don t do this!!!

32 LEDs Diode an electronic device which passes current in one direction only

33 LEDs 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

34 LEDs 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

35 LEDs Negative pressure; no flow possible

36 LEDs No pressure; resistance to flow is large

37 LEDs Small pressure; resistance to flow decreases

38 LEDs Medium pressure; resistance to flow still decreasing

39 LEDs High pressure; resistance to flow small

40 LEDs Very high pressure; resistance almost zero

41 LEDs + - Diode symbol and physical appearance

42 LEDs off off V 0.7 I small; changes slowly

43 LEDs off on V 0.7 I large; almost independent of V

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

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

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

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

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

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

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

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

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

53 LEDs The resistor can go before or after the LED.

54 LEDs The resistor can go before or after the LED.

55 LEDs Reverse-biased, the LED won t light up.

56 LEDs Reverse-biased, the LED won t light up.

57 Bipolar Junction Field Effect There are several types of transistor; each is a three terminal device.

58 Bipolar Junction Field Effect There are several types of transistor; each is a three terminal device. The most common types of transistors are BJTs and FETs.

59 Bipolar Junction Field Effect There are several types of transistor; each is a three terminal device. The most common types of transistors are BJTs and FETs. are often used in voltage dividers to act as variable resistors.

60 Bipolar Junction Field Effect

61 Bipolar Junction Field Effect collector

62 Bipolar Junction Field Effect collector emitter

63 Bipolar Junction Field Effect base collector emitter

64 Bipolar Junction Field Effect V s V i 0.7 V o V s if V i 0.7 I c 0 if V i 0.7

65 Bipolar Junction Field Effect V s V i 0.7 V o V s if V i 0.7 I c 0 if V i 0.7

66 Bipolar Junction Field Effect V s V i > V o = V s I c R if V i > 0.7 I c I b if V i > 0.7

67 Bipolar Junction Field Effect BJTS are current amplifiers; a small base current controls a much larger collector/emitter current.

68 Bipolar Junction Field Effect BJTS are current amplifiers; a small base current controls a much larger collector/emitter current. You should always have a base resistor with a BJT!

69 Bipolar Junction Field Effect FETS are voltage amplifiers; a small gate voltage controls a much larger drain/source current. Actually it s the voltage between the gate and the source which matters.

70 Bipolar Junction Field Effect

71 Bipolar Junction Field Effect drain

72 Bipolar Junction Field Effect drain source

73 Bipolar Junction Field Effect gate drain source

74 Bipolar Junction Field Effect V supply V gs V o I 0 if V gs V gson E (ehancement mode) FET

75 Bipolar Junction Field Effect V supply V gs V o = V DS E (ehancement mode) FET

76 Bipolar Junction Field Effect V supply V gs = 0 gate V o V supply if V gs < V gson E (ehancement mode) FET

77 Bipolar Junction Field Effect V supply V gs V gson gate V o = V DS > 0 if V gs V gson E (ehancement mode) FET

78 Bipolar Junction Field Effect V supply V gs >> V gson gate V o = V DS 0 if V gs >> V gson E (ehancement mode) FET

79 Bipolar Junction Field Effect FETS are voltage amplifiers; a small gate-source voltage controls a much larger drain/source current.

80 Bipolar Junction Field Effect FETS are voltage amplifiers; a small gate-source voltage controls a much larger drain/source current. You do not use a gate resistor with an FET!

81 Bipolar Junction Field Effect FETS are voltage amplifiers; a small gate-source voltage controls a much larger drain/source current. You do not use a gate resistor with an FET! All FETs work in enhancement mode; some also work in depletion mode.

82 Bipolar Junction Field Effect V supply V gs = 0 gate V o = V DS > 0 if V gs = 0 D (depletion mode) FET

83 Bipolar Junction Field Effect V supply V gs V o 2 I 0 if V gs V th < 0 V gs has to be negative to turn off. D (depletion mode) FET

84 Bipolar Junction Field Effect V supply V gs V o = V DS 0 if V gs >> 0 D (depletion mode) FET

85 Bipolar Junction Field Effect V supply V gs 0 gate V o = V DS > 0 if V gs 0 D (depletion mode) FET

86 Bipolar Junction Field Effect V supply V gs >> 0 gate V o = V DS 0 if V gs >> 0 D (depletion mode) FET