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).
- 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.