help me identify this diode

Discussion in 'General Electronics Chat' started by omaroski, Apr 29, 2009.

  1. omaroski

    Thread Starter Active Member

    Jun 19, 2008
    34
    0
    What kind of diode is the CR26 in the schematics? There's also a code on its body: M 02 00 48 but couldn't find anything. Is it some zener being reverse polarized? Thanks for your help!

    [​IMG]
     
  2. greendean

    Member

    Dec 20, 2008
    19
    0
    6 6v can also be writen 6v6.

    i dont know what the 6v6 is.
    but i installed a 6v2 today and it's a little glass zener diode.

    dont know if that helps
     
  3. Wendy

    Moderator

    Mar 24, 2008
    20,765
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    Last edited: Apr 29, 2009
  4. Darren Holdstock

    Active Member

    Feb 10, 2009
    262
    11
    I agree, it's got to be a zener. It sets the reference voltage for the transistor constant current source that charges the batteries, that current being (Vz-Vbe)/R23 (or R23 in parallel with R24 if switched to "FAST").
     
  5. omaroski

    Thread Starter Active Member

    Jun 19, 2008
    34
    0
    Sorry for poor quality, however it's 6.8 v right. I need to change this component because it's shorted. Thanks for confirmation.
    The voltage R22+CR26 should give the voltage on C21, C21=R22+CR26, right?

    the link outputs a table about Resitor Standards?! :confused:
     
  6. Darren Holdstock

    Active Member

    Feb 10, 2009
    262
    11
    It looks like a 6V8, and indeed the voltages add up. There's a strange ground arrangement in that circuit, where the 0V reference is taken between the two batteries, so that means the voltages written on the base and emitter look very odd.

    Ideally you want to know the voltage across C21 so you can work out the dissipation of the zener by finding the current through R22, and hence the current through zener CR26, and hence the zener power dissipation. It's not clear from the circuit what the voltage across C21 is, except that it's (hopefully) less than 65 V, so it's probably best just to measure it; it won't make much difference if you do this while the zener is shorted. Ignore the transistor base current if you like, and the answer for the zener dissipation will err on the side of caution.

    Zeners tend to fail short-circuit if they're over-dissipated, or receive a bit of a transient current surge. It doesn't hurt to pick one that has a power rating a fair bit higher than needed on average.
     
  7. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    Yes. But voltage across C21 can readily be worked out from the schematic.

    Its about 46V. (Cr25+battery+Q2 base_voltage+zener)
     
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