regarding diode

Discussion in 'Homework Help' started by gaya3eeee, Aug 23, 2006.

  1. gaya3eeee

    Thread Starter New Member

    Aug 18, 2006
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    why resistors used in testing "the forward and reverse characteristics of diode" gets burned when high current is passed?
     
  2. Dave

    Retired Moderator

    Nov 17, 2003
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    I'm sorry but I don't understand the question, can you clarify what exactly you are asking? You may benefit from reading this.

    Dave
     
  3. n9352527

    AAC Fanatic!

    Oct 14, 2005
    1,198
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    Umm... because the resistor power rating is too low?
     
  4. Papabravo

    Expert

    Feb 24, 2006
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    High current in a resistor causes heat which must be dissipated by conduction, convection, or radiation. To compute the power in a resistor you square the current and multiply by the resistor value. If the current is expressed in Amperes and the resistance is expressed in Ohms then the power will be expressed in Watts.

    Example: An IR-LED has the desired brightness at a forward current of 150 mA at a forward voltage drop of 2.2 Volts. The supply is +5 VDC. The resistor for this application is 18 Ohms. Compute the required power dissipation rating of the resistor
    Code ( (Unknown Language)):
    1.  
    2. (0.150)*(0.150)*18 = 405 mWatts
    3.  
    If you use a quarter watt resistor in this application the magic smoke will very quickly exit the resistor body with the usual fetid acrid smell.

    Remember the following piece of doggerel:

    "Twinkle-twinkle little star
    Power's equal I squared R"
     
  5. Gadget

    Distinguished Member

    Jan 10, 2006
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    What voltages are you using..?
     
  6. Dave

    Retired Moderator

    Nov 17, 2003
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    Electronics for pre-schools :D

    Love the ditty.

    Dave
     
  7. Papabravo

    Expert

    Feb 24, 2006
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    Twinkle-twinkle little star
    Voltage equals I times R
     
  8. Dave

    Retired Moderator

    Nov 17, 2003
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    Twinkle-twinkle little star
    Current equals V by R

    I can play this too :D

    Dave
     
  9. Papabravo

    Expert

    Feb 24, 2006
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    Never a dull moment with this crowd. Nothing better than snappy repartee.
     
  10. Dave

    Retired Moderator

    Nov 17, 2003
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    You know it makes sense ;)

    Dave
     
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