OBJECTIVES

2. OBJECTIVES After studying Chapter 14, the reader should 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 around 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 ESD.

3. 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. • When another material is added to a semiconductor material in very small amounts, it is called doping.

4. N-TYPE MATERIAL • N-type material is silicon or germanium that is doped with an element such as phosphorus, arsenic, or antimony, each having five electrons in its outer orbit. FIGURE 14-1 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.

5. P-TYPE MATERIAL • P-type material is produced by doping silicon or germanium with the element boron or the element indium. • These impurities have only three electrons in their outer shell and, when combined with the semiconductor material, result in a material with seven electrons, one electron less than is required for atom bonding.

6. P-TYPE MATERIAL FIGURE 14-2 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. HOW HOLES MOVE • 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 holes movement is called the hole theory of current flow.

8. HOW HOLES MOVE • The holes move in the direction opposite that of electron flow. FIGURE 14-3 Unlike charges attract and the current carriers (electrons and holes) move toward the junction.

9. SUMMARY OF SEMICONDUCTORS • The following is a summary of semiconductor fundamentals. • The two types of semiconductor materials are P type and N type. N-type material contains extra electrons; P-type material contains holes due to missing electrons. • In P-type semiconductors, electrical conduction occurs mainly as the result of holes (absence of electrons). • Hole movement results from the jumping of electrons into new positions. • Under the effect of a voltage applied to the semiconductor, electrons travel toward the positive terminal and holes move toward the negative terminal.

10. DIODES • 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.

11. DIODES FIGURE 14-4 A diode is a component with P- and N-type material together. The negative electrode is called the cathode and the positive electrode is called the anode.

12. DIODES FIGURE 14-5 Diode connected to a battery with correct polarity (+ to + and - to -). Current flows through the diode. This condition is called forward bias.

13. DIODES FIGURE 14-7 Diode symbol and electrode names. FIGURE 14-6 Diode connected with reversed polarity. No current flows across the junction between the P-type and N-type material. This connection is called reverse bias.

14. ZENER DIODES • A zener diode is a specially constructed diode designed to operate with a reverse-bias current. • Zener diodes can be constructed for various breakdown voltages and can be used in a variety of automotive and electronic applications, especially for electronic voltage regulators.

15. ZENER DIODES FIGURE 14-8 A zener diode blocks current flow until a certain voltage is reached, then it permits current to flow.

16. CLAMPING DIODES • Diodes can be used as a high-voltage clamping device when the power (+) is connected to the cathode (-) of the diode. • A diode connected across the terminals of a coil to control voltage spikes is called a clamping diode. FIGURE 14-9 (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.

17. CLAMPING DIODES • Diodes were first used on AC compressor clutch coils at the same time electronic devices were first used. FIGURE 14-10 Spike protection diodes are commonly used in computer-controlled circuits to prevent damaging high-voltage surges that occur anytime current flowing through a coil is stopped.

18. ZENER DIODE DESPIKING PROTECTION • Zener diodes can also be used to control high-voltage spikes and keep them from damaging delicate electronic circuits. FIGURE 14-11 A zener diode is commonly used inside automotive computers to protect delicate electronic circuits from high-voltage spike. A 35 volt zener diode will conduct any voltage spike resulting from the discharge of a coil safely to ground through a current-limiting resistor in series with the zener diode.

19. DESPIKING PROTECTIVE RESISTORS • All coils must use some protection against high-voltage spikes that occur when the voltage is removed from any coil. • Instead of a diode installed in parallel with the coil windings, a resistor can be used and is called a spike protection resistor. FIGURE 14-12 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.

20. DESPIKING PROTECTIVE RESISTORS • Resistors are often preferred for two reasons. • Coils will usually fail when shorted rather than open, as this shorted condition results in greater current flow in the circuit. • The protective diode can also fail, and diodes usually fail shorted before they blow open.

21. DIODE RATINGS • Most diodes are rated according to their maximum current flow in the forward-bias direction and their resistance to high voltage in the reverse-bias direction. • This rating of resistance to reverse-bias voltage is called the peak inverse voltage (PIV) rating, or the peak reverse voltage (PRV) rating.

22. DIODE RATINGS • Typical 1 ampere diodes use a code that indicates the PIV rating. • For example: • 1N 4001-50 V PIV • 1N 4002-100 V PIV • 1N 4003-200 V PIV • 1N 4004-400 V PIV • 1N 4005-600 V PIV

23. LIGHT-EMITTING DIODES • Light-emitting diodes (LEDs) radiate light when current flows through the diode in the forward-bias direction. FIGURE 14-13 Typical LED. The longer of the two electrodes of an LED is the anode. Some LEDs use equal-length electrodes, and determination of which electrode to connect to which polarity must be made using an ohmmeter or the “diode check” position of a digital meter.

24. PHOTODIODES • All P-N junctions emit energy, mostly in the form of heat or light such as with an LED. • Photodiodes are specially constructed to respond to various wavelengths of light with a “window” built into the housing. FIGURE 14-14 Typical photodiodes.

25. PHOTODIODES FIGURE 14-15 Symbol for a photodiode. The arrows represent lights striking the P-N junction of the photodiode.

26. 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

27. PHOTORESISTORS FIGURE 14-16 Either symbol may be used to represent a photoresistor.

28. VARISTORS • Varistors are resistors whose resistance depends on the level of voltage applied. • A varistor, or metal oxide varistor (MOV), operates similarly to two back-to-back zener diodes.

29. SILICON-CONTROLLED RECTIFIERS • 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. FIGURE 14-17 Symbol and terminal identification of an SCR.

30. SILICON-CONTROLLED RECTIFIERS FIGURE 14-18 Wiring diagram for a CHMSL.

31. THERMISTORS • A thermistor is a semiconductor material such as silicon that has been doped to provide a given resistance. FIGURE 14-19 Symbols used to represent a thermistor.

32. RECTIFIER BRIDGES • A rectifier bridge is a group of diodes that is used to change alternating current into direct current. • A rectifier bridge is used in alternators to rectify the alternating current produced in the stator (stationary windings) of the generator (alternator).

33. RECTIFIER BRIDGES FIGURE 14-20 This rectifier bridge contains six diodes; three on each side and mounted in an aluminum-finned unit to help keep the diode cool during generator (alternator) operation.

34. TRANSISTORS • 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. FIGURE 14-21 Bipolar transistors use P- and N-type materials to form the three parts of a transistor. The P- and N-type materials can be arranged either as a PNP transistor or an NPN transistor. The difference is in how the transistor is turned on or off. Positive voltage to the base turns on an NPN transistor whereas a lower or negative voltage is necessary to turn on a PNP transistor.

35. TRANSISTORS • The center section of a transistor is called the base; it controls current flow through the transistor FIGURE 14-22 The three parts of a transistor are the emitter (E), the base (B), and the collector (C).

36. TRANSISTORS FIGURE 14-23 The symbols and parts of a typical bipolar transistor. Notice that the arrow is always on the emitter and points toward the N-type material.

37. HOW A TRANSISTOR WORKS • 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.

38. HOW A TRANSISTOR WORKS FIGURE 14-24 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.

39. 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.

40. FIELD-EFFECT TRANSISTORS • Field-effect transistors (FETs) have been used in most automotive applications since the mid-1980s. • They use less electrical current and rely mostly on the strength of a small voltage signal to control the output.

41. FIELD-EFFECT TRANSISTORS FIGURE 14-25 The three terminals of a field-effect transistor (FET) are called the source, gate, and drain.

42. DARLINGTON PAIRS • A Darlington pair consists of two transistors wired together. • This arrangement permits a very small current flow to control a large current flow. FIGURE 14-26 A Darlington pair consists of two transistors wired together, allowing a very small current to control a large current flow.

43. 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.

44. SOLID-STATE, INTEGRATEDCIRCUIT, AND DUAL-INLINE PACKAGE COMPONENTS • Solid-state components are used in many electronic semiconductors and/or circuits. • They are called “solid state” because they have no moving parts, just higher or lower voltage levels within the circuit.

45. SOLID-STATE, INTEGRATEDCIRCUIT, AND DUAL-INLINE PACKAGE COMPONENTS • Newer-style electronic devices use the same components, but they are now combined (integrated) into one group of circuits, and are thus called an integrated circuit (IC). • Integrated circuits are usually encased in a plastic housing called a CHIP with two rows of inline pins; this arrangement is called the dual inline pins (DIP) chips.

46. SOLID-STATE, INTEGRATEDCIRCUIT, AND DUAL-INLINE PACKAGE COMPONENTS FIGURE 14-27 Typical dual inline package chip with identifying information explained.

47. HEAT SINK • Heat sink is a term used to describe any area around an electronic component that, because of its shape or design, can conduct damaging heat away from electronic parts. • Examples of heat sinks include the following: • Ribbed electronic ignition control units • Cooling slits and cooling fan attached to a generator (alternator) • Special heat-conducting grease under the electronic ignition module in all General Motors HEI systems

48. PHOTOTRANSISTORS • Similar in operation to a photodiode, a phototransistor uses light energy to turn on the base of a transistor. • Phototransistors are frequently used in steering wheel controls. FIGURE 14-28 Symbols for a phototransistor: (a) shows a line for the base; (b) does not show a line for the base.

49. SOLAR CELLS • Solar cells are another type of semiconductor device where light energy is used to produce a small current flow by dislodging electrons within the structure.

50. HOW TO TEST DIODES AND TRANSISTORS • Diodes and transistors can be tested with an ohmmeter. FIGURE 14-29 To check a diode, select “diode check” on a digital multimeter. The display will indicate the voltage drop (difference) between the meter leads. The meter itself applies a low-voltage signal (usually about 3 volts) and displays the difference on the display. (a) When the diode is forward biased, the meter should display a voltage between 0.500 and 0.700 V (500 mV to 700 mV). (b) When the meter leads are reversed, the meter should read OL (over limit) because the diode is reverse biased and blocking current flow.