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Basic Electronics

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basicelex

Text of Basic Electronics

  • Solid State UniversityUnderstand the following components:PotentiometersThermistorsCapacitorsDiodesZener DiodesTransistors

  • PotentiometersDifferentiate between potentiometers and rheostats A rheostat changes current flow in a series circuit A potentiometer is a voltage sensor in parallel

  • RheostatLess resistance

  • RheostatMore resistance

  • Potentiometer

  • 4 voltPotentiometerVery low current

  • 2 voltPotentiometerUsed as a sensor

  • 2.5 volt (should be 2 volt)Potentiometerpoor ground

  • 5 volt (should be 2 volt)Potentiometeropen ground

  • Rheostats are wired in series with the loadtheir purpose is to change amp flow Potentiometers sense motioncheck for: reference voltage good ground un-interrupted signal

  • 4.52 V0.52 V

  • MIL lamp lit. TPS codeWhat is wrong?

  • ThermistorsThermistors change resistance with temperature

    Negative Temperature Coefficient thermistors decrease in resistance when they heat

    Commonly used to sense changing temperatures

  • 4.52 VHot or Cold?COLD!

  • 1.53 VHot or Cold?HOT!

  • Gauge reads colder than actual temperature

  • Gauge reads colder than actual temperature

  • Gauge reads colder than actual temperature

  • ThermistorsThermistors are checked with an Ohmmeter or a Voltmeter A temperature probe or thermometer should be used when checking

  • CapacitorsCapacitors store an electrical charge Capacitors provide an alternate path for electrons and act as a current shock absorber Capacitors are commonly used to suppress noisealternatorscoilsmotors

  • CapacitorsCapacitors are rated in microfarads Capacitors are connected in parallel with a load they can be checked with an ohmmeter for short or open circuits

  • Find the Capacitor

  • EMI & RFIWhen coils turn off they self induce and create a voltage surge this surge can create electromagnetic interference and radio frequency interference capacitors absorb this surge to dampen interference

  • SemiconductorsConductors have 3 or fewer electrons in the valence ring of the atomcopper has one aluminum has three Insulators have 5 or more electrons in the valence ring of the atom

  • SemiconductorsElements with four valence electrons are not good as insulators or conductors Silicon, when is a crystal form, shares valence electrons to make a good insulator Silicon can be doped to add electrons to the valence ring or remove electrons from the valence ring

  • SemiconductorsSilicon doped with phosphorous (which has five electrons in the valence ring) will create an N type semiconductor Silicon doped with boron (which has three electrons in the valence ring) will create a P type semiconductor

  • DiodesPlacing an N type semiconductor with a P type will create a diode. In a forward biased diode current will flow with a small amount of resistance Too much current will overheat and destroy the diode

  • DiodesReverse biasing a diode will create very high resistance at the center of the diode and current will not flow Too much voltage will overcome the internal resistance and the diode will short out

  • Arrow shows conventional theory (hole flow) Diodes wired like this will block current

  • Arrow shows conventional theory (hole flow) Diodes wired like this will allow current to flow with a slight voltage drop

  • Testing DiodesDiodes require .2 - .6 volts to forward bias Digital ohmmeters may not supply this voltage with ohm check use diode check feature when using DVOM

  • Testing DiodesShorted diodes on alternators will allow A/C voltage that may confuse a control module Routine checks with oscilloscope are easy

  • Anti- Spike DiodesClamping or Anti-Spike diodes protect sensitive control modules

  • Anti- Spike Diodes

    Functioning anti spiking diodes will exhibit un-equal resistance when reversing polarity (using an analogue meter)

  • Failure in Anti- Spike DiodesAn open, or shorted diode will damage computer control modules Open diodes allow spike voltages to harm electronic components Shorted diodes (and relay coil windings) will cause too much current to flow and burn out switching transistors in computers

  • Testing Anti- Spike DiodesOpen diodes will show equal resistance with reversed polarity (using an analogue meter) Shorted diodes will show equal, and low resistance

  • Open Diode

  • Shorted Diode

  • Good Diode

  • Good Diode

  • Types of DiodesPositive diodeNegative diode Zener Diode Light Emitting Diode (LED)

  • TransistorsTransistors can act as a relay they use a small signal current to control a larger working current Transistors can act as a signal amplifier

  • PNP transistorPoints In Permanently Will conduct current when the base sees a Negative polarity

  • NPN transistorNever Points In Base must be Positive to allow transistor to conduct current

  • TransistorsTransistors are damaged by too much current Transistors are damaged by high voltage