Circuit bacics (1)– Diode

diode

Diode blocks current in one direction while letting current flow in another direction.
 junction diodes are common: put a pice of N type silicon next to a piece of P type silicon.
  • N material has excess negative charge (electrons);
  • P material has excess positive material (holes).
Characteristics:
  • Diode is forward biased when Vanode > Vcathode (usually 0.7Volts, needed to start the hole-electron combination process at the junction).
    • Conducts current strongly.
    • Voltage drop across diode is (almost) independent of diode current.
    • Effective resistance (impedance) of diode is small.
  • Diode is reverse biased when Vanode < Vcathode.
    • Conducts current very weakly (perhaps 10 microamps)
    • Diode current is (almost) independent of voltage, until breakdown (the junction breaks down and lets current through if you apply enough reverse voltage).
    • Effective resistance (impedance) of diode is very large.
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