junction DIODE

 bridge rectifier (4 DIODE package 4 leads, 2 DC, 2 AC)

Diodes are the simplest of the semiconductors in that they have only one junction.
Their common characteristic is the ability to conduct in only one direction (most of the time)

They are used for a variety of important functions such as >>>

  • rectification in power supplies


  • detection in AM + FM radios
    Image result for crystal radio set   
  • a crystal radio uses no external power - a germanium crystal is used as a diode to detect the signal

  • Carrier Wave = local examples 680am 740am 102.1fm 107fm

  • Modulation - shaping a carrier wave so that information is carried on the
    carrier wave
  • AM = amplitude modulation
  • FM = Frequency modulation

  • Tuning = selecting the carrier wave of the station that you want to listen to it is mposed of a variable resonant circuit composed of an inductor (coil) and capacitor

  • Detection = rectifying the tuned in carrier wave to strip the information or lower frequencey audio that we hearImage result for detection of am radio signal animation

  • Amplification is the process of strengthening the signal so that is strong enough to drive a speaker = audible

    wireless devices are everywhere now and will play a greater role in the IoT internet of everything


  • light source in LEDs
    note long lead is anode


  • energy transduction from light to electricity in Photovoltaics
    - the solar cell is simply a naked diode that transduces photon energy into electron energy

    - hold an LED up to the sun and it will generate 1.7 volts (its a photo diode working in reverse now!)

  • typically a transducer can change energy in 2 directions
  • motors - generators
  • speakers - microphones
  • photocells - LEDS
  • piezoelectric crystals


  • voltage regulation in power supplies





    voltage regulator



    Zener diodes are used to regulate the out put voltage of power supplies so that changing load characteristics have little or no effect on the voltage supplied
    ( within a limited range)

    - important were constant voltage is essential such as digital circuits and other voltage sensitve loads and where volatage sources exceed the limits of the


 Component   Circuit Symbol  Function of Component
Diode diode symbol A device which only allows current to flow in one direction.
Light Emitting Diode
LED symbol A transducer which converts electrical energy to light.
Zener Diode zener diode symbol A special diode which is used to maintain a fixed voltage across its terminals AKA regulator
Photodiode AKA
solar cell
photodiode symbol A light-sensitive diode.
Germanium Diode diode symbol has a forward Voltage of 0.2 V and is used in signal detection circuits