Electronic fundamentals

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Electronic fundamentals

• Diodes
• Thermistors
• Transistors
• Heat sinks
• Causes of failure
• Electrostatic discharge

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Diodes

• Allows current to travel in one direction only
• Used in alternators as part of a rectifier bridge
  (group of diodes) to control current flow in one
  direction
• Also used in computer controls, climate control
  circuits, and other electronic systems on the
  automobile

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Diodes
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Diodes

• Zener diodes a diode that blocks reverse-bias
  current up to a certain voltage
• Above the breakdown voltage point, a zener diode
  will conduct current without damage to itself
• Ideally suited as an electronic voltage regulator
• Also used in fuel injector circuits as a clamp

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Diodes

• Clamping diodes used to suppress high voltage
  spikes whenever a coil is turned off
• Installed across coil leads to redirect the high
  voltage spike back through the coil windings
• Commonly used on A/C clutches

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Zener Diodes
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Diodes

• Resistors can sometimes be used in place of
  diodes for controlling high voltage spikes
• Coils often fail shorted rather than open
• This condition results in greater current flow in
  the circuit which a diode cannot control
• A resistor wired in parallel can reduce spikes if
  a coil shorts out
• Often found in climate control solenoids

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Two different methods of spike suppression
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Diodes

• Light emitting diodes (LED)
• Diodes that radiate light when current flows
  through in a forward bias direction
• LEDs produce very little heat
• More efficient because energy consumed is
  converted directly to light
• Faster reacting than incandescent

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Diodes

• Checking diodes for proper operation

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Thermistors

• A thermistor is a semiconductor that changes
  resistance according to temperature
• As a voltage is applied, the resistance drops as
  temperature increases
• Referred to as NTC negative temperature
  coefficient
• Commonly used for coolant and intake air
  temperature sensors

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Thermistors
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Transistors

• A transistor is a semiconductor that will allow
  current flow if certain electrical conditions
  allow it to switch on
• Used on an automobile for the following purposes
• An electrical switch
• To amplify current in a circuit
• To regulate current in a circuit

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Transistors

• Acts as two back to back diodes that can conduct
  current in one direction only
• If the base current is turned on, the current
  flow from the collector to the emitter can be
  turned on or off
• The current controlling the base is called the
  control current

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Transistors
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Heat sinks

• A heat sink is something designed to conduct
  damaging heat away from electronic parts
• Ribbed electronic ignition control units
• Cooling slits and fan attached to a generator
• Special heat conducting grease applied to modules
  mounting bases

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Causes of failures

• Poor connections
• Heat
• High voltage spikes
• Excessive current
• Improper polarity
• Electrostatic discharge

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Electrostatic discharge

• Static charges build up on a human body whenever
  movement occurs
• When a conductive material is touched, the static
  charge is rapidly discharged
• Can cause severe damage to electronic components

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Electrostatic discharge

• If you can feel it it is at least 3000 volts
• If you can hear it it is at least 5000 volts
• If you can see it it is at least 10000 volts

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Electrostatic discharge

• Keep electronic components in protective wrapping
  until ready to install
• Before handling any electronic component, ground
  yourself to a good conductor
• Do not touch component terminals