1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice

Zener diode test current, Izt help

Discussion in 'General Electronics Chat' started by MbTaNk16, May 11, 2008.

  1. MbTaNk16

    MbTaNk16 New Member

    Joined:
    Apr 9, 2008
    Messages:
    5
    Likes:
    0
    I'm a beginner at electronics and I wanted to buy a 5.1V zener diode with a Pd of 500mW. I've noticed that the test current (Izt) of these diodes are either 50uA, 5mA, or 20mA. I have two questions:

    1) What exactly is zener test current?

    2) What's the significance of this and how would it affect an electronic circuit?
     
  2. RODALCO

    RODALCO Well-Known Member

    Joined:
    May 21, 2006
    Messages:
    1,232
    Likes:
    43
    Location:
    Akld, New Zealand
    5V1 Zener

    Most zener diodes 400mW rating, work properly at the rated zenervoltage at a 5 to 10 mA current flow through the zener.

    Say you have a 12 volts supply, have the series resistor to allowe a 10 mA currentflow through the zener.

    For a 5.1 volt zener 6.9 volts has to be dissipated in a resistor.
    From U=I*R 6.9=0.01*R therefore R = 690 ohms.

    A 680 ohms E12 ¼ Watt resistor will suffice.
     
  3. RODALCO

    RODALCO Well-Known Member

    Joined:
    May 21, 2006
    Messages:
    1,232
    Likes:
    43
    Location:
    Akld, New Zealand
    You can use the zener voltage, as a fixed reference voltage, which will remain reasonably stable with power supply voltages ranging from about 8 to 18 Volts in the 12 volts example.

    Bear in mind not to exceed the zener power rating and try to keep the zener current within 5 - 15 mA range.
     
  4. dave

    Dave New Member

    Joined:
    Jan 12, 1997
    Messages:
    -
    Likes:
    0


     
  5. eblc1388

    eblc1388 Active Member

    Joined:
    Jan 25, 2005
    Messages:
    2,228
    Likes:
    18
    Location:
    UK

    The voltage across a zener diode is not constant but depends on the current flowing in the diode.

    This effect is especially noticable in those low voltage zeners of a few volts. For example, a 3.6V zener in my component box have a breakdown voltage of only 2.95V at less than 1mA current, 3.3V at ~3mA and 3.6V at about 5mA or more.

    Therefore to specify a zener diode, the manufacturer will typically use a certain constant current to test them.

    For an user, if you want the zener to give you a fairly stable and accurate voltage, you have to supply the zener with a stable current.
     
  6. MbTaNk16

    MbTaNk16 New Member

    Joined:
    Apr 9, 2008
    Messages:
    5
    Likes:
    0
    Understood

    Thanks guys that cleared everything up! Thanks for the fast responses too!;)
     
  7. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,449
    Likes:
    937
    Location:
    Canada, of course!
    ONLINE
    A zener diode that has a test voltage at a low current has a much higher voltage at a higher current.
    A zener diode with a high test current might not regulate the voltage at a low current.

    EDITED
     
    Last edited: May 12, 2008
  8. icemonster

    icemonster New Member

    Joined:
    Dec 16, 2009
    Messages:
    2
    Likes:
    0
    Hi all,
    Do u know about zener ?? Zener has internal resistance and other action,so could u tell me all bout this,please?? I'm welling to know, who could answer to me? And i hope so,thanks!!
     
  9. MikeMl

    MikeMl Well-Known Member Most Helpful Member

    Joined:
    Mar 17, 2009
    Messages:
    11,057
    Likes:
    541
    Location:
    AZ 86334
    Read this link or this link.
     
    Last edited: Aug 17, 2010
  10. icemonster

    icemonster New Member

    Joined:
    Dec 16, 2009
    Messages:
    2
    Likes:
    0
    Hello Mike', Thanks for helpin'!!! :)*
     

Share This Page