AUT 242

1. AUT 242 Chapter 14 Electronic Fundamentals

2. OBJECTIVES After studying Chapter 14, the reader will be able to: • Prepare for ASE Electrical/Electronic Systems (A6) certification test content area “A” (General Electrical/Electronic Systems Diagnosis). • Identify semiconductor components. • Explain precautions necessary when working with semiconductor circuits. • Discuss where various electronic and semiconductor devices are used in vehicles. • Describe how to test diodes and transistors. • List the precautions that a service technician should follow to avoid damage to electronic components from electrostatic discharge.

3. Anode Base Bipolar transistor Burn in Cathode CHMSL Clamping diode Collector Control current Darlington pair Despiking diode Diode Doping Dual inline pins (DIP) Emitter ESD FET Forward bias Gate Germanium Heat sink Holes Hole theory Impurities Integrated circuit (IC) Inverter Junction Light emitting diode (LED) MOSFET NPN transistor NTC N-type material Op-amps Photodiodes Photons Photoresistor Phototransistor Peak inverse voltage (PIV) Peak reverse voltage (PRV) PNP transistor P-type material PWM Rectifier bridge Reverse bias SCR Semiconductors Silicon Spike protection resistor Suppression diode Thermistor Threshold voltage Transistor Zener diode KEY TERMS

4. SEMICONDUCTORS • Semiconductors are materials that contain exactly four electrons in the outer orbit of their atom structure and are, therefore, neither good conductors nor good insulators. • EXAMPLES OF SEMICONDUCTORS • CONSTRUCTION • N-TYPE MATERIAL • P-TYPE MATERIAL

5. SEMICONDUCTORS • N-type material. Silicon (Si) doped with a material (such as phosphorus) with five electrons in the outer orbit results in an extra free electron.

6. SEMICONDUCTORS • P-type material. Silicon (Si) doped with a material, such as boron (B), with three electrons in the outer orbit results in a hole capable of attracting an electron.

7. What Is the Hole Theory? • Current flow is expressed as the movement of electrons from one atom to another. In semiconductor and electronic terms, the movement of electrons fills the holes of the P-type material. Therefore, as the holes are filled with electrons, the unfilled holes move opposite to the flow of the electrons. This concept of hole movement is called the hole theory of current flow. The holes move in the direction opposite that of electron flow. For example, think of an egg carton, where if an egg is moved in one direction, the holes created move in the opposite direction.

8. What Is the Hole Theory? • Unlike charges attract and the current carriers (electrons and holes) move toward the junction.

9. DIODESCONSTRUCTION • A diode is an electrical one-way check valve made by combining a P-type material and an N-type material. • The word diode means “having two electrodes.” • Electrodes are electrical connections: The positive electrode is called the anode; the negative electrode is called the cathode. • The point where the two types of materials join is called the junction.

10. DIODESCONSTRUCTION • A diode is a component with P-type and N-type materials together. The negative electrode is called the cathode and the positive electrode is called the anode.

11. DIODESOPERATION • The N-type material has one extra electron, which can flow into the P-type material. • The P type has a need for electrons to fill its holes. • Diode connected to a battery with correct polarity (battery positive to P type and battery negative to N-type). Current flows through the diode. This condition is called forward bias.

12. DIODESOPERATION • Diode connected with reversed polarity. No current flows across the junction between the P-type and N-type materials. This connection is called reverse bias.

13. DIODESOPERATION • Diode symbol and electrode names. The stripe on one end of a diode represents the cathode end of the diode.

14. What Is the Difference Between Electricity and Electronics? • Electronics usually means that solid-state devices are used in the electrical circuits. Electricity as used in automotive applications usually means electrical current flow through resistance and loads without the use of diodes, transistors, or other electronic devices.

15. Burn In” to Be Sure • A common term heard in the electronic and computer industry is burn in, which means to operate an electronic device, such as a computer, for a period from several hours to several days. • Most electronic devices fail in infancy, or during the first few hours of operation. This early failure occurs if there is a manufacturing defect, especially at the P-N junction of any semiconductor device. The junction will usually fail after only a few operating cycles.

16. Burn In” to Be Sure • What does this information mean to the average person? When purchasing a personal or business computer, have the computer burned in before delivery. This step helps ensure that all of the circuits have survived infancy and that the chances of chip failure are greatly reduced. Purchasing sound or television equipment that has been on display may be a good value, because during its operation as a display model, the burn-in process has been completed. The automotive service technician should be aware that if a replacement electronic device fails shortly after installation, the problem may be a case of early electronic failure.

17. ZENER DIODESCONSTRUCTION • A zener diode is a specially constructed diode designed to operate with a reverse-bias current. • OPERATION • A zener diode acts as any diode in that it blocks reverse-bias current, but only up to a certain voltage. • Above this certain voltage (called the breakdown voltage or the zener region), a zener diode will conduct current without damage to the diode.

18. HIGH-VOLTAGE SPIKE PROTECTIONCLAMPING DIODES • (a) Notice that when the coil is being energized, the diode is reverse biased and the current is blocked from passing through the diode. The current flows through the coil in the normal direction. • (b) When the switch is opened, the magnetic field surrounding the coil collapses, producing a high-voltage surge in the reverse polarity of the applied voltage. • This voltage surge forward biases the diode, and the surge is dissipated harmlessly back through the windings of the coil.

19. HIGH-VOLTAGE SPIKE PROTECTIONCLAMPING DIODE APPLICATION • A diode connected to both terminals of the air- conditioning compressor clutch used to reduce the high voltage spike that results when a coil (compressor clutch coil) is de-energized.

20. HIGH-VOLTAGE SPIKE PROTECTIONCLAMPING DIODE APPLICATION • Spike protection diodes are commonly used in computer-controlled circuits to prevent damaging high voltage surges that occur any time current flowing through a coil is stopped.

21. HIGH-VOLTAGE SPIKE PROTECTIONDESPIKING ZENER DIODES • A zener diode is commonly used inside automotive computers to protect delicate electronic circuits from high-voltage spikes. • A 35 volt zener diode will conduct any voltage spike resulting from the discharge of the fuel injector coil safely to ground through a current-limiting resistor in series with the zener diode.

22. HIGH-VOLTAGE SPIKE PROTECTIONDESPIKING RESISTORS • A despiking resistor is used in many automotive applications to help prevent harmful high-voltage surges from being created when the magnetic field surrounding a coil collapses when the coil circuit is opened.

23. DIODE RATINGS • SPECIFICATIONS • DIODE VOLTAGE DROP

24. DIODE RATINGS • SPECIFICATIONS • Most diodes are rated according to: • Maximum Current Flow (forward biased) • How much current can it take before it fails. • 1 to 5 amperes for most automotive applications. • PIV (peak inverse voltage) or PRV (peak reverse voltage) • How much reverse bias voltage can the diode stand before it fails.

25. DIODE RATINGS • DIODE VOLTAGE DROP • The voltage drop across a diode is about the same as the voltage required to “forward bias” the diode. • Geranium diode = .3 to .5 Vdc • Silicone diode = .5 to .7 Vdc • When testing with a DVOM in the diode-check position most diodes will show a .5 to .7 voltage drop.

26. LIGHT-EMITTING DIODESOPERATION • All diodes radiate some energy during normal operation. • Most diodes radiate heat because of the junction barrier voltage drop (typically 0.6 volt for silicon diodes). • Light emitting diode (LED) radiate light when current flows through the diode in the forward-bias direction.

27. LIGHT-EMITTING DIODESOPERATION • A typical light-emitting diode (LED). • Normally a 300 to 500 ohm, 0.5 watt resistor is required to be attached in series with the LED, to control current flow to about 0.020 A (20 mA) or damage to the P-N junction may occur.

28. LIGHT-EMITTING DIODESNEED FOR CURRENT LIMITING • If an LED were connected across a 12 volt automotive battery, the LED would light brightly, but only for a second or two. • Excessive current (amperes) that flows across the P-N junction of any electronic device can destroy the junction. • A resistor must be connected in series with every diode (including LEDs) to control current flow across the P-N junction.

29. How Does an LED Emit Light? • An LED contains a chip that houses P-type and N-type materials. The junction between these regions acts as a barrier to the flow of electrons between the two materials. When a voltage of 1.5 to 2.2 volts of the correct polarity is applied, current will flow across the junction. As the electrons enter the P-type material, it combines with the holes in the material and releases energy in the form of light (called photons ). The amount and color the light produces depends on materials used in the creation of the semiconductor material. • LEDs are very efficient compared to conventional incandescent bulbs, which depend on heat to create light. LEDs generate very little heat, with most of the energy consumed converted directly to light. LEDs are reliable and are being used for taillights, brake lights, daytime running lights, and headlights in some vehicles.

30. Photodiodes - Purpose • Photodiodes are often used to transmit/receive information. • Photo diode receives light signal from an led in the steering wheel to transmit information from the wheel mounted push buttons. • Photodiodes may be used in conjunction with LED’s in the engine for crank position sensors and/or ignition triggers.

31. PHOTODIODESPURPOSE AND FUNCTION • Typical photodiodes. • They are often built into a plastic housing so that the photodiode itself may not be visible.

32. PHOTODIODESCONSTRUCTION • Symbol for a photodiode. The arrows represent light striking the P-N junction of the photodiode.

33. Either symbol may be used to represent a photoresistor. PHOTORESISTORS • A photoresistor is a semiconductor material (usually cadmium sulfide) that changes resistance with the presence or absence of light. • Dark = High resistance • Light = Low resistance

34. Photoresistors - Uses • Photoresistors are often used in self-dimming mirrors and to control headlight dimmer relays

35. SILICON-CONTROLLED RECTIFIERSCONSTRUCTION • A silicon-controlled rectifier (SCR) is commonly used in the electronic circuits of various automotive applications. • An SCR is a semiconductor device that looks like two diodes connected end to end.

36. SILICON-CONTROLLED RECTIFIERSUSES OF AN SCR • SCRs can be used to construct a circuit for a center high-mounted stoplight (CHMSL) .

37. THERMISTORSCONSTRUCTION • A thermistor is a semiconductor material such as silicon that has been doped to provide a given resistance. • When the thermistor is heated, the electrons within the crystal gain energy and electrons are released.

38. THERMISTORSUSES OF THERMISTORS • A thermistor is commonly used as a temperature-sensing device for coolant temperature and intake manifold air temperature. • Symbols used to represent a thermistor.

39. RECTIFIER BRIDGESDEFINITION • A rectifier bridge is a group of diodes that is used to change alternating current (AC) into direct current (DC). • This rectifier bridge contains six diodes; the three on each side are mounted in an aluminum-finned unit to help keep the diode cool during alternator operation.

40. TRANSISTORSPURPOSE AND FUNCTION • A transistor is a semiconductor device that can perform the following electrical functions. • Act as an electrical switch in a circuit • Act as an amplifier of current in a circuit • Regulate the current in a circuit

41. TRANSISTORSPURPOSE AND FUNCTION • CONSTRUCTION • TRANSISTOR SYMBOLS • HOW A TRANSISTOR WORKS • HOW A TRANSISTOR AMPLIFIES FIGURE 14–22 Basic transistor operation. A small current flowing through the base and emitter of the transistor turns on the transistor and permits a higher amperage current to flow from the collector and the emitter.

42. Construction • A transistor is similar to two back-to-back diodes that can conduct current in only one direction. • A transistor will allow current flow if the electrical conditions allow it to switch on, in a manner similar to the working of an electromagnetic relay.

43. Is a Transistor Similar to a Relay? • Yes, in many cases a transistor is similar to a relay. • Both use a low current to control a higher current circuit. • A relay can only be on or off. A transistor can provide a variable output if the base is supplied a variable current input.

44. Comparison between the control (low current) and the high current circuits of a transistor compared to a mechanical relay. Is a Transistor Similar to a Relay?

45. TRANSISTORS • The center section of a transistor is called the base; it controls current flow through the transistor • The three parts of a transistor are the emitter (E), the base (B), and the collector (C).

46. TRANSISTORSPURPOSE AND FUNCTION • Basic transistor operation. A small current flowing through the base and emitter of the transistor turns on the transistor and permits a higher amperage current to flow from the collector and the emitter.

47. What Does the Arrow Mean on a Transistor Symbol? • The arrow on a transistor symbol is always on the emitter and points toward the N-type material. The arrow on a diode also points toward the N-type material. To know which type of transistor is being shown, note which direction the arrow points. • PNP: pointing in • NPN: not pointing in

48. TRANSISTOR GAIN • A transistor can do more than switch on and off when the base is triggered. Most transistors can also amplify. • In an NPN transistor, for example, if the base voltage is higher than emitter voltage (by about 0.6 volt or more), current will flow from collector to emitter.

49. HOW A TRANSISTOR AMPLIFIES • A transistor can amplify a signal if the signal is strong enough to trigger the base of a transistor on and off. • The resulting on–off current flow through the transistor can be connected to a higher-powered electrical circuit.

50. What Is a Darlington Pair? • A Darlington pair consists of two transistors wired together. This arrangement permits a very small current flow to control a large current flow. • The Darlington pair is named for Sidney Darlington, an American physicist for Bell Laboratories from 1929 to 1971. • Darlington amplifier circuits are commonly used in electronic ignition systems, computer engine control circuits, and many other electronic applications.