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zener diod

Discussion in 'General Electronics Chat' started by fayyaz0346, May 19, 2011.

  1. fayyaz0346

    fayyaz0346 New Member

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    in cell phone repair field we are useing zener diod in series circuit is it ok ??
     

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  2. crutschow

    crutschow Well-Known Member Most Helpful Member

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    Depends upon what you are trying to do.
     
  3. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi,

    All the cell phone chargers i have seen output 5v not 12v.
     
  4. dave

    Dave New Member

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  5. ronv

    ronv Well-Known Member Most Helpful Member

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    Are you trying to reduce the 12 volts to 5 volts?
     
  6. Jaguarjoe

    Jaguarjoe Member

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    In the top circuit the zener is forward biased, therefor it is not acting like a zener, it is simply providing ~0.6v of a voltage drop. That's probably why there's an "X" mark after the circuit.
    In the second circuit the zener will operate properly as a simple shunt regulator if "R" is correctly chosen. That's probably why it has a "√" mark after it.
     
    Last edited: May 19, 2011
  7. RCinFLA

    RCinFLA Well-Known Member

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    Cellphone draws significant current 300 mA for small voice only to 1000 mA for smartphone. The best way to go from 12v to 5v at this amount of current is with a switching regulator.

    There are many very inexpensive cigarette lighter charger adaptors on the market to do this job.
     
  8. fayyaz0346

    fayyaz0346 New Member

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    hi, in cell phone repair the charging ic replacment is not easy therefre a zener diod is used but in series main idea is to directly connect 5v dc charger + line to battery which is 3.6 vdc this is not a good idea but we have to do this. i know that it is wrong but teacher says use zener in series circuit.i want to know the value of resister to drop 5vdc to 3.6 vdc through zener diod.
     
  9. tytower

    tytower Banned

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    No one came back yet so if it helps a zener diode dumps voltage to negative. So if you want 3.6 V on the line then the zener must be 12V-3.6V= 8.4V.
    8.4V will dump to neg leaving 3.6V to use-I think that's how it goes
    Better put some current limiting in though however suits. Say 100 ohms on the top line and 100 ohms on the zener line would allow a reasonable current to flow
     
    Last edited: May 21, 2011
  10. Jaguarjoe

    Jaguarjoe Member

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    If the 12v input is not adequately filtered/regulated for the expected load then all the crap that rides on the 12v line will appear on the 3.6v output of the zener. All the zener is doing is subtracting 8.4v from whatever is fed into it.
    If you have a 12v supply and take 8.4v away for a zener then 3.6v more for a phone, there is no more voltage left for a current limiting resistor.
     

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