Most Important Points | Diodes | Part-II | Competitive Examination

Most Important Points | Diodes | Part-II | Competitive Examination

Suitable for the post of Junior Engineer in BSNL, DMRC, DRDO, PTCUL, RRB, UPCL, etc examination.

  1. Diode is a Non-Linear device.

  2. The ac component present in the dc output of rectifier is called ripple.

    • For full wave rectifier ripple frequency fr = 100 Hz.

  3. Inductor passes low frequency and blocks high frequency signals.

    • Initially inductor acts as open circuit and after charging acts as short circuit.

  4. Capacitor passes high frequency and blocks low frequency signals.

  5. Zener Diode is a special purpose diode designed to operate in breakdown region.

    • Zener Diode is used as Voltage Regulator.

    • To Check whether the zener diode is operating in breakdown region OR not. We find Vth across load. If Vth>Vz then zener diode will act in breakdown region otherwise not.

  6.  Zener effect occurs below 4 or 5 V reverse voltage.

    • Temperature co-efficient is negative for zener effect working diode. If temperature increase by 1 degree centigrade, breakdown voltage decrease by 1.4 mV.

  7. Avalanche effect occurs above 6 V reverse voltage.

    • Temperature co-efficient is positive for avalanche effect working diode. If temperature increase by 1 degree centigrade, breakdown voltage increase by 2 mV.

  8. Light Emitting Diode (LED) is a special purpose diode which emits light when forward biased.

    • LED is made of Gallium, Arsenic and Phosphorous.

    • LED produces non-coherent light.

  9. When light falls on the P-N Junction of photo diode, it is dislodges the valence electrons from their orbit producing free electrons and holes in the process.

  10. Opto-coupler combines a LED and a photo-diode.

    • It provides electrical isolation.

  11. Light Amplification by Stimulated Emission of Radiation (LASER) produces coherent light (Light waves are in same phase to each other).

    • LASER is used in communication, medical, defense etc.

  12. Schottky Diode is a special purpose diode with almost zero reverse recovery time. It is used at high frequencies where short switching time are needed.

    • Reverse recovery time is the time a diode takes to shut off after it is suddenly switched from forward to reverse bias.

    • Used in digital devices above 300 MHz (SMPS).

    • It has high speed turn OFF Barrier potential 0.25 V.

    • It has metal such as Gold, Silver or Platinum on one side of junction and doped silicon (N-type) on the other side.

    • It has no depletion layer so no stored charges at junction.

  13. The width of depletion layer increases with the reverse voltage. This is why the capacitance of a varactor diode can be controlled by the reverse voltage.

    • Used in TV and Radio receivers for tuning.

    • Tuning range of varactor depends on the doping level.

  14. Lighting, Power line faults and transients can pollute the ac line voltage by superimposing dips and spikes.

    • Dips are reverse voltage drops lasting microseconds or less.

    • Spikes are very brief over-voltages up to 2000 V or more.

    • This semiconductor device is like two back to back zener diodes with a high breakdown voltage in both directions.

    • Used as transient suppressor for line filtering.

  15. Tunnel Diode exhibits negative resistance phenomenon i.e. increase in forward voltage produces a decrease in forward current.

    • It is a voltage control device.

    • The negative resistance of tunnel diodes is useful in high frequency circuits called oscillators.

  16. PIN Diode operate as a variable resistor at RF and microwave frequencies.

    • When diode is forward biased, it acts like a current controlled resistance.

    • When diode is reverse biased, it acts like a fixed capacitor.

    • Used in microwave communications, as RF switches, attenuators, photo-detectors and phase shifters.

Author: Mr. Amarjeet Singh Jamwal, Assistant Loco Pilot, Ambala Division, INDIAN RAILWAY.

Reference: Albert Malvino and David J Bates, “Electronic Principles”, 7th Edition, TATA McGRAW HILL.

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