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Chapter 10

Chapter 10. Diodes. Semiconductors. Germanium 32 protons Silicon 14 protons Most commonly used. Atomic Physics. How many electrons can be in the ground state of an atom? Answer: 2 (s level) ...in the first excited state? Answer: 8 (s and p levels) …in the second excited state?

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Chapter 10

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  1. Chapter 10 Diodes

  2. Semiconductors • Germanium • 32 protons • Silicon • 14 protons • Most commonly used

  3. Atomic Physics • How many electrons can be in the ground state of an atom? • Answer: 2 (s level) • ...in the first excited state? • Answer: 8 (s and p levels) • …in the second excited state? • Answer: 8 (s and p levels)

  4. Valence Electrons • Valence electrons are electrons in the outermost shell of the atom that can participate in forming chemical bonds with other atoms. • How many valence electrons does Silicon have? • Answer: 4

  5. How many electrons are needed to fill the outermost energy level of Silicon? • Answer: 4 • 2-D representation of Silicon Crystal • How many valence electrons does Phosphorus (15P) and Aluminum (13Al) have? • Answers: 5 and 3

  6. Diodes • Conduct electricity in one direction • Two terminal devices • anode and cathode • Primarily made of silicon

  7. DopingThe adding of impurities • n-type crystal • e.g. Silicon doped with Phosphorous • negative charge carriers • electrons • p-type crystal • e.g. Silicon doped with Aluminum • positive charge carriers • vacancy or hole

  8. Diodes Circuit Symbol p-type n-type

  9. Flapper Valve Analogy Flapper Valve Analogy

  10. Diode Characteristics • Forward-Bias Condition • Good Conductor • Reverse-Bias Condition • High Resistance • I versus V Plot • Ideal Diode and Real Diode • “Knee” and Breakdown Voltage • Three Regions

  11. Shockley Equation • Shockley Equation on Excel • Common LED have a maximum recommended current of 20mA. • What resistor value is needed in series with an LED and a 5-Volt power supply so that the LED does not burn up?

  12. What does the circuit symbol for an LED look like?

  13. Diode Circuits • rec·ti·fi·erPronunciation: 'rek-t&-"fI(-&)rFunction: nounDate: 1611: one that rectifies; specifically: a device for converting alternating current into direct current • Half-Wave Rectifier • Full-Wave Rectifier • Bridge Rectifier

  14. Smoothing Capacitors • Ripple Voltage (Vr) • DC Component (VDC) • Ripple Factor

  15. Concept Test • Is a high or low value for the ripple voltage DV desirable? • Answer: Low • What are three ways to achieve low ripple voltages? • Answers: • Low Current • High Frequency • High Capacitance

  16. Zener Diodes • Zener Diodes are intended to operate in the breakdown region. • Manufacturers set the breakdown voltage by modifying the doping. • Zener diodes can make good voltage regulators. • Circuit Symbol • Clarence Zener once visited SFA.

  17. What is a Zener diode? How do the circuit symbols for a diode and a Zener diode differ? • Zener diodes are intended to operate in the breakdown region -usually as voltage regulators. • Manufacturers set the breakdown voltage by careful doping.

  18. How do you convert AC to DC? AC Input Diode Rectifier Smoothing Capacitor Voltage Regulators remove the ripple. DC Output Voltage Regulator

  19. Concept Question • What components to you need to convert a 110-Volt AC signal to a 9-Volt DC signal? • Answers: • Transformer – to step down the voltage • Diodes – to rectify the waveform (make +) • Capacitor – to smooth the rectified waveform • Voltage Regulator – to remove the ripple • Note that the device connected to this 9-Volt power supply acts as a resistor. • For this reason the device is sometimes called the “load” or “load resistance”.

  20. Example Questions 10.32, 35 Homework Questions? 10.55, 56, 57, 35

  21. What is an ideal diode? • An ideal diode is a perfect conductor with zero voltage drop in the forward bias direction… • …and a perfect insulator in the reverse bias direction.

  22. What element from the periodic table are diodes made of? • Silicon

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