Connect with us

Zener diodes not working

Discussion in 'General Electronics Discussion' started by Mark Korvin, Apr 5, 2017.

Scroll to continue with content
  1. Mark Korvin

    Mark Korvin

    3
    0
    Apr 5, 2017
    I'm having problems getting a couple of different 12 volt zener diodes (1 watt & 5 watt) to work. When connected to an unregulated power source of 16-18 volts with different series resistors (75, 470, 1k ohm) the voltage measred across the zener is in the range 13-15 volts - the breakdown doesn't seem to be kicking in.
    Any suggestions on what could.be going wrong?
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,839
    Jan 21, 2010
    What voltage are you seeing? Less than a volt or the 16 to 18 volts?

    Are you measuring across the zener? Or across the zener and the resistor? Or something else?
     
  3. Mark Korvin

    Mark Korvin

    3
    0
    Apr 5, 2017
    Across the zener.
    Following a suggestion from another thread I tried hooking up a couple of 9 volt batteries in series with a 10k resistor to the zener diode. Supply voltage was about 23 volts, resistor 9 volts and zener 14 volts. Same outcome with a replacement zener...
     
  4. Audioguru

    Audioguru

    3,394
    733
    Sep 24, 2016
    Were the zener diodes very cheap and were sold on ebay?
    Was your voltmeter very cheap and was sold on ebay?
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,839
    Jan 21, 2010
    With a 10K resistor, the voltage across the zener is likely to be slightly lower than the specified voltage. The fact that you're seeing a higher voltage is suggestive that your zener is not a 12V device.
     
  6. Audioguru

    Audioguru

    3,394
    733
    Sep 24, 2016
    9V/10k= 0.9mA, a very low current for a power zener diode. A 1N5349B 12V/5W zener diode is tested at 100mA. It might be 11.5V at 5mA.
     
  7. Mark Korvin

    Mark Korvin

    3
    0
    Apr 5, 2017
    Put a new battery in the multimeter and the problem looks to be resolved. Didn't seem to be complaining about low battery but definitely made a difference. Nothing worse than 'fake' readings.!
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,839
    Jan 21, 2010
    Hahahaha, I have a multimeter like that. The low battery indication is that it becomes very inaccurate. :-(
     
  9. Audioguru

    Audioguru

    3,394
    733
    Sep 24, 2016
    Doesn't your multimeter have a "low battery" indication before its calibration fails?
     
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,839
    Jan 21, 2010
    In my case, no. And you can imagine how much use it gets now.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-