chap38 pps Automotive technology at University of Cambridge

start Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 OBJECTIVES: After studying Chapter 38, 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 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 OBJECTIVES: After studying Chapter 38, the reader should be able to: • • • 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 (ESD) Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 KEY TERMS: anode base • bipolar transistor • burn in cathode • center high-mounted stoplight (CHMSL) • clamping diode • CMOS • collector • control current darlington pair • despiking diode • diode • doping • dual inline pins (DIP) electrostatic discharge (ESD) • emitter FET • forward bias Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 KEY TERMS: gate • germanium heat sink • hole theory • holes impurities • integrated circuit (IC) • junction light-emitting diode (LED) • metal oxide varistor (MOV) • MOSFET negative temperature coefficient (NTC) • NPN transistor • Ntype material • OP-amps Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 KEY TERMS: peak inverse voltage (PIV) • peak reverse voltage (PRV) • photodiodes • photons • photoresistor • phototransistor • PNP transistor • polarity • P-type material • PVM rectifier bridge • reverse bias saturation • semiconductors • silicon • silicon-controlled rectifier (SCR) • solar cells • spike protection resistor • suppression diode thermistor • threshold voltage • transistor • TTL varistors • zener diode Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Electronic components are the heart of computers Knowing how electronic components work helps take the mystery out of automotive electronics Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SEMICONDUCTORS Semiconductors are neither conductors nor insulators Flow of electrical current is movement of electrons in materials having fewer than four electrons in the atom’s outer orbit Insulators contain more than four electrons in their outer orbit and cannot conduct electricity Semiconductors contain exactly four electrons in the outer orbit of their atom structure and are neither good conductors nor good insulators Two examples of semiconductor materials are germanium and silicon, which have no free electrons to provide current flow However, both can be made to conduct current if another material is added to provide conditions for electron movement Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 When another material is added in very small amounts, it is called doping The doping elements are called impurities; and therefore, after their addition, the germanium and silicon are no longer considered pure elements The material added represents only one atom of impurity for every 100 million atoms of the pure semiconductor material The resulting atoms are still electrically neutral, because the number of electrons still equals the protons of the combined materials These combined materials are classified into two groups depending on the number of electrons in the bonding between the two materials; N-type or P-type materials Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 N-TYPE MATERIAL N-type material is silicon or germanium doped with an element such as phosphorus, arsenic, or antimony, each having five electrons in its outer orbit These five electrons are combined with the four electrons of the silicon or germanium to total nine electrons There is room for only eight electrons in the bonding between the semiconductor material and the doping material This leaves extra electrons, and even though the material is still electrically neutral, these extra electrons tend to repel other electrons outside the material See Figure 38–1 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 38–23 A typical automotive computer with the case removed to show all of the various electronic devices and integrated circuits (ICs) The large red and orange devices are ceramic capacitors Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 PHOTOTRANSISTORS Similar in operation to a photodiode, a phototransistor uses light energy to turn on the base of a transistor A phototransistor is an NPN transistor that has a large exposed base area to permit light to act as the control for the transistor A phototransistor may or may not have a base lead If not, they have only a collector and emitter lead When the phototransistor is connected to a powered circuit, the light intensity is amplified by the gain of the transistor Figure 38–24 Symbols for a phototransistor (a) uses the line for the base; (b) does not Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 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 Solar cells are stacked and/or grouped in large sections to enable them to supply useful amounts of current Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 HOW TO TEST DIODES AND TRANSISTORS Diodes and transistors can be tested with an ohmmeter The diode or transistor being tested should be disconnected from the circuit for best results Use the diode-check position on a digital multimeter A low-voltage reading with the meter leads attached both ways across a diode means that the diode is shorted and must be replaced An OL reading with the meter leads attached both ways across a diode means that the diode is open and must be replaced See Figure 38–25 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 38–25 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 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 (a) Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman (b) ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 ELECTRONIC COMPONENT FAILURE CAUSES While electronic ignition modules, electronic voltage regulators, onboard computers, and other electronic circuits are generally very reliable, failure can occur Frequent causes: Poor Connections It has been estimated that most engine computers returned as defective have simply had poor connections at the wiring harness terminal ends These faults are often intermittent and hard to find Heat The operation and resistance of electronic components and circuits are affected by heat Electronic components should be kept as cool as possible and never hotter than 260°F (127°C) Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Voltage Spikes A high-voltage spike can literally burn a hole through semiconductor material The source of these high-voltage spikes is often the discharge of a coil without proper (or with defective) despiking protection A poor electrical connection at the battery or other major electrical connection can cause high-voltage spikes to occur, because the entire wiring harness creates its own magnetic field, similar to that formed around a coil If the connection is loose and momentary loss of contact occurs, a high-voltage surge can occur through the entire electrical system To help prevent this type of damage, ensure that all electrical connections, including grounds, are properly clean and tight Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Excessive Current All electronic circuits are designed to operate within a designated range of current (amps) If a solenoid or relay is controlled by a computer circuit, the resistance of that solenoid or relay becomes a part of that control circuit If a coil winding inside the solenoid or relay becomes shorted, the resulting lower resistance will increase current through the circuit Even though individual components are used with current-limiting resistors in series, coil winding resistance is also used as a currentcontrol component in the circuit If a computer fails, always measure resistance across all computercontrolled relays and solenoids It should be within specs (generally over 20 ohms) for each component computer controlled Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 ELECTROSTATIC DISCHARGE Electrostatic discharge (ESD) is created when static charges build up on the human body whenever movement occurs These charges, although just slightly painful to us, cause severe damage to delicate electronic components The following are typical static voltages: If you can feel it, it is at least 3,000 volts If you can hear it, it is at least 5,000 volts If you can see it, it is at least 10,000 volts Although these voltages seem high, the current, in amperes, is extremely low However, sensitive electronic components such as vehicle computers, radios, and instrument panel clusters can be ruined if exposed to as little as 30 volts Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 This is a problem, because harm can occur to components at voltages lower than we can feel To prevent damage to components, follow these easy steps: Keep the replacement electronic component in the protective wrapping until just before installation Before handling any electronic component, ground yourself to a good conductor to drain away any static charge Do not touch the terminals of electronic components HINT: When cleaning electronic contacts, use a pencil eraser This cleans the contacts without harming the thin protective coating used on most electronic terminals Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Blinking LED Theft Deterrent - Part A blinking (flashing) LED consumes only about milliamperes (5/1,000 of one ampere or 0.005 A) Most alarm systems use a blinking red LED to indicate that the system is armed A fake alarm indicator is easy to make and install When the ignition is turned off, the power flows through the LED to ground and the LED flashes To prevent distraction during driving, the LED goes out whenever the ignition is on Therefore, this fake theft deterrent is “auto setting” and no other action is required to activate it when you leave your vehicle except to turn off the ignition and remove the key as usual Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Blinking LED Theft Deterrent - Part An easy-to-make fake alarm indicator A 470-ohm 1/2-watt resistor limits current flow to prevent battery drain The positive terminal (anode) of the diode is connected to a fuse that is hot at all times, such as the cigarette lighter The negative terminal (cathode) of the LED is connected to any ignition-controlled fuse Figure 38–26 Schematic for a blinking LED theft deterrent Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY Semiconductors are constructed by doping semiconductor materials such as silicon N-type and P-type materials can be combined to form diodes, transistors, SCRs, and computer chips Diodes can be used to direct and control current flow in circuits and to provide despiking protection Transistors are electronic relays that can also amplify Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY (cont.) All semiconductors can be damaged if subjected to excessive voltage, current, or heat Never touch the terminals of a computer or electronic device; static electricity can damage electronic components Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 end Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458