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PN Junction Diodes

PN Junction Diodes. Current Flow. Some Diodes. Small signal silicon diodes. Power Rectifiers. Surface mount diodes. Miscellaneous diodes from the junk box. A Canadian band from the 1980’s. Doping of Semiconductors.

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PN Junction Diodes

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  1. PN Junction Diodes Current Flow

  2. Some Diodes Small signal silicon diodes Power Rectifiers Surface mount diodes Miscellaneous diodes from the junk box A Canadian band from the 1980’s

  3. Doping of Semiconductors The addition of a small percentage of foreign atoms in the regular crystal lattice of silicon or germanium produces dramatic changes in their electrical properties, producing n-type and p-type semiconductors. Pentavalent Trivalent

  4. P and N Type Semiconductors P-type N- type

  5. Formation of Depletion Region anode cathode

  6. Reverse Bias No appreciable current flow Depletion region widens

  7. Forward Bias Depletion region narrows Substantial current flows

  8. Current-versus-Voltage (IV) Characteristic Curve

  9. Avalanche Breakdown Thermally excited electrons cause a leakage current to flow in the reverse bias state. These electrons accelerate in the bias field, picking up energy, and collide with the lattice, releasing more electrons. At sufficiently high field strength the process achieves a runaway condition called avalanche.

  10. Zener Diodes Zener diodes have well-controlled and specified avalanche voltages. The avalanche or zener voltage is often used to establish stable reference potentials in circuits.

  11. Schottky Diodes Schottky diodes are formed with metal/semiconductor junctions They exhibit lower forward voltage drops and higher switching speeds between forward and reverse states. Reverse leakage currents tend to be higher than with PN junction diodes.

  12. Varicap Tuning Diodes In reverse bias, a diode exhibits capacitance between its terminals. As the reverse bias potential increases, the depletion region grows wider and capacitance decreases. As the reverse bias potential decreases, the depletion region narrows and the capacitance increases. Diodes that are designed specifically to be voltage-variable capacitors are called varicaps. Virtually all modern radio and television receivers, as well as cell-phones, handy-talkies, etc. are tuned by varicap diodes.

  13. Next Steps Explore diode properties with curve tracer in lab. Investigate use of diode as half-wave rectifier.

  14. Half Wave Rectifier

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