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Do 2 x 1 watt diodes = 1x 2 watt ZD?

Discussion in 'Hobby Electronics' started by shannell, Oct 22, 2003.

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  1. shannell

    shannell Guest

    I am trying to get a 2 watt 5.1 volt zener diode, I bought 2 x 1 watt zener
    diodes, if I put them in parrallel, do they work the same as a 2w 5.1v ZD?
  2. Ken Taylor

    Ken Taylor Guest

    In theory, yes, but it's not a good practice as they aren't perfect devices
    and won't load share 100%. What are you actually trying to do? There may be
    a better solution.

  3. shannell

    shannell Guest

    Hi, I am trying to quieten the 80mm 12v fans on a CRT projector.
    Any reccommendations? Dick smith only had the 1 watters...
  4. Justin Thyme

    Justin Thyme Guest

    Unfortunately no - they have a tolerance in them, so one might be 5.11v and
    the other 5.09v. When they are in parallel, the 5.09v one will take all the
    current, because the voltage is still below the threshold of the 5.11v.
    Consequently one zener will be drastically overloaded while the other does
    nothing at all.
    There are ways around it however - careful use of appropriate value
    resistors can overcome the problem. i'm not the best at doing ascii circuit
    diagrams, and it's maybe a little hard to explain. if you want more info
    i'll post a sketch on the web and give you a link.
    Alternatively - have you considered the use of 7805 devices? - they are
    simple to design around and can comfortably deliver fairly high currents -
    up to 1A with suitable heatsinking.
  5. Rod Speed

    Rod Speed Guest

    Not in his situation where he's just chucking some voltage away.

    It should work well enough.
  6. Would be better to put two with half voltage in series.
    Much more tolerant to small differences between diodes.

  7. Rod Speed

    Rod Speed Guest

    True. Dunno how available they are tho.
  8. crt projectors get HOT!!! do you really want to put more heat stress on the
    unit, best thing to do is get a quieter fan or mod the air-flow path a bit.
  9. Franc Zabkar

    Franc Zabkar Guest

    "Chucking some voltage away"? What a load of gibberish.
    No, it is a silly idea.

    - Franc Zabkar
  10. Spajky

    Spajky Guest

    see my site under electronics; fan stuff II next page, dirty zener
    enhancement ...

    -- Regards, SPAJKY
    & visit site -
    Celly-III OC-ed,"Tualatin on BX-Slot1-MoBo!"
    E-mail AntiSpam: remove ##
  11. Hello Shannell,
    Ken's question was spot on.
    Have a look here for starters.
    Have a look at the LM317 tutorial if you don't like the PWM circuits.

    If you don't like the LM317 idea, maybe a string of several ordinary
    diodes in series would do. You could mount them on a rotary
    switch. Introduce roughly 0.8 volt (drop across each diode) on
    each click of the switch till the fan noise reduces to suit you.

    I see DSE has 1 amp diodes for 7 cents each and 3 amp diodes
    for 25 cents. How much current does your fan draw?
    Find out and choose your diodes.

    Here is another site where the author has gone
    into this fan noise problem in a big way also.

    Have fun!

    John Crighton
  12. Guest

    Reduction of the airflow into the projector could shorten the lifetime
    of some components due to elevated heating of these components. These
    could be lamps, the crts, which would probably depend on circulation
    of cooling fluids on the screen of the tube via convection anyway,
    electrolytic capacitors, most semiconductors, etc.

    If you can try to find out the manufacturer of the fans, and the model
    of the fan, then you can identify the amount of airflow the fan pushes
    into the projector. You could then attempt to select a low noise fan
    that has an airflow (typically measured in litres/minute|hour) that
    is equivalent or greater than the existing fans. Low noise fans typically
    have lower flow rates than equivalent size fans.

    RS Components and Farnell have a selection of 80mm fans, both 240 volt ac,
    and 12 volt dc. Others in this ng could recommend other suppliers.

    Then again, if you modify the projector in any way, you could void the
    warranty, if it's still valid. If it's out of the warranty period, then
    I'd recommend you employ a qualified tv technician/repairman to carry
    out the required modifications. Also, there may be a modification
    sheet from the projector manufacturer that details how to fix a noisy
    fan problem.



    Reply to

    dmmilne at ozemail dot com dot au
  13. Arpit

    Arpit Guest

    use a slower speed 120mm fan. quieter, and more airflow.
  14. Rod Speed

    Rod Speed Guest

    Some stupid wog claiming to be
    message just the puerile shit thats always pouring from its lard arse.
  15. Franc Zabkar

    Franc Zabkar Guest

    FWIW, WES Components have 5W, 5.1V Zeners for ~$1 each. You could also
    make up a string of eight 1N4004 diodes in series. Having said that, I
    believe reducing the airflow is not a good idea.

    - Franc Zabkar
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