Manipulating Current with Diodes

Semiconductor Devices and the P-N Junction:

  • Basis of most Semiconductors - PN Junction.
Energy band diagrams for conductors, insulators, and semiconductors.
  • The above shown EG diagrams are fundamentally correct. But, in order to understand the depth, we use the diagram shown below (example - introducing the concept of direct/indirect bandgap S/Cs).

  • Properties are based on the Valence shell.
  • Example of a poor conductor - Rubber.
  • But, we are interested in the Semiconductors.
    • Silicon: 
      • 4 valence shell electrons.
      • N-Type S/C (abbreviated for Semiconductor): Pentavalent Dopant (shown below).
      • Dopant has 5 electrons in the valence shell (P).
      • Doping: Vaporize P with heat and diffuse it over pure Si - You can control it with pressure, temperature, and so forth . . .
      •  Similarly, we dope for P-Type S/C.

The P-N Junction:

PN Junction at equilibrium.

  • When Sandwiched at the atomic level, the charge interface region called the depletion region (acts like energy barrier).
  • Forward Biasing the P-N Junction:

    • Reverse Biasing the P-N Junction:

    • The Diode: A device that allows current to flow only in one direction.

    • Forward bias is usually in the range of 0.3V for Germanium-based diodes and 0.7V for Silicon-based diodes to initiate conduction.

    • Diode Circuit:
    Diode Circuit with forward bias.
    • Diode Characteristics - Example:
    Instantaneous Forward Voltage of a Diode: Forward Characteristics.
    *Log Values.
    • Tip: to know more about the particular diode, check out the datasheet of the respective diode for its characteristics.

    • Types of Diodes:
    Various diode packages and types.
    • Other types - Schottky diode (symbol: similar to Zener diode): Have very low forward voltages (turns on/off very quickly).
    • LEDs: 1.7V(Red side) - 3.1V (Blue side).
    • Black or White stripe on one side of the diode body indicates the Cathode.
    • Bridge rectifier: has FOUR diodes in it (AC <> DC).
    Example Part Numbers (Diodes):

    1N4006: Silicon Rectifier diode.

    1N4001: White bar - Cathode.

    1N4001 (different manufacturer).

    1N4001 - Glass Passivated.

    STPS 2L60 (702): Schottky Diode - used in power systems to steer power.

    1N4739A (9.1V Zener diode)

    1N751 fairchild: Zener diode (5.1V).

    • The Schottky diode on power rails - rectification.
    Example 2: Forward V-drop vs Forward I (STPS2L60).

    • Silicon Rectifier Diode or simply Rectifier Diode: 1N4001
    Forward Biased Rectifier Diode.

    After reverse biasing the diode, we can read small amount of current (literally small values). You can see the multimeter on the right reading the leakage current (~0.1uA). But, in the forward direction, we can get up to 2A of current flow! Interesting isn't it? 😃

    *For ratings and features, check the datasheet(s) online.
    **Wire guage (AWG Size) - lower the number => higher diameter.
    ***Read more about diodes and their modeling equations on Wikipedia (click here).


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