how can I identify zener diodes?

Discussion in 'General Electronics Chat' started by matelot, Apr 15, 2013.

  1. matelot

    Thread Starter Member

    Apr 15, 2013
    I have a box full of little glass components, I put it that way because I know some i.e 1n4148 arn't zener diodes but I think most are.
    For instance, I have a lot just marked H48 and some marked BZX 33.
    I assume 5.1 b3 is a 5.1volt zener but is there any way of safely testing for zeners, what the breakdown voltage is etc?
  2. atferrari

    AAC Fanatic!

    Jan 6, 2004
    Nice subject for a friend of my cousin who works with Google.

    I will call him home this Saturday.
  3. russ_hensel

    Distinguished Member

    Jan 11, 2009
    Apply a reverse bias thru a resistor and raise the voltage until you observe zener behavior.
  4. KnRele

    New Member

    Jan 7, 2013
    I would use a variable voltage supply able to deliver from 0 to 30 V, and the familiar combination of a series resistor and the zener connected with anode negative and cathode positive. Selecting the resistor for a voltage drop of 25 V at 40 mA (as an example) would be about right for a 5.1V zener diode.

    All the zeners have some preferred reverse-bias current that they need in order to operate; looking at the data sheet for the 1N4728-1N4764 series of zeners as an example, the test currents there ranges from 76 mA for the 1N4728 which is 3.3V to 2.5mA for the 1N4764 which is a 100V device. For the 1N4751 at 30V, the test current is 8.5 mA.

    The idea is to feed some reasonably appropriate current through the unknown zener; not too much so it burns out, and not too little so it doesn't manage to break-down correctly.

    Place a voltmeter across the zener and slowly raise the voltage of the supply, then when the zener hits the constant-reverse voltage area, you can get an approximate idea of what voltage the zener is.

    If the diode never breaks down, that is, the voltage across it remains close to the voltage from the power supply, the diode is either a zener of higher voltage (I happened across some 150V ones a while ago) or they could be other kinds of diodes, such as small-signal, Schottky, or varicap.

    But this should allow you to locate all the lower-voltage diodes.
    PackratKing likes this.