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Do diodes need to be put in, in a certain direction?

  1. Jul 12, 2007 #1
    I was given a christmas present and i have now begun making it and ive run into a problem,:confused: does the colour code on diodes relate to where and what direction that they need to be soldered into? please respond
  2. jcsd
  3. Jul 12, 2007 #2


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    Diodes are polarity sensitive devices. So the direction they are soldered matters. Usually a color band, dot, or color code bands identifies the cathode (negative). When you solder your diode make sure that you have the cathode pointing to the (more) negative terminal of your power source.
    The color bands mean the diode type: example 139 semiconductor diode.
  4. Jul 12, 2007 #3
    for zener diodes it can conduct both ways, sometimes people put zener with the cathode to +voltage and anode to gnd to clamp the voltage (maintain it) or act as a voltage regulator.

    best to look at the manufacturer part and refer to datasheet
  5. Jul 12, 2007 #4
    i think one wire is longer than the other, thats how u can tell, but i forget which one is which
  6. Jul 12, 2007 #5


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    When we have this, such as the case with LEDs; shorter means cathode.
  7. Jul 12, 2007 #6
    oh, woops, i thpought he was only talking about LED's
  8. Jul 21, 2007 #7
    from The symbol of diode ;

    and you should put the postive voltage at the base of the square and the -ve at the other side

    on the dide you will see a wide black band this represent the st.line close to the top of triangle
  9. Jul 21, 2007 #8
    Also you shoud put a resistance in series with the diode
  10. Jul 23, 2007 #9
    there is always a silver ring on each pn junction diode on one side,
    the side having the silver ring is always negative or you can say that this is N-side
    and the other side is P-side.
    This explanation is only for normal pn junction diodes. There are many more kind of diodes
    having different indications for p and n type.
    diode is always connected in forward bias, in reverse bias diode act as an open switch.
    I hope you are satisfied with my answer.
    Best Regards!
  11. Jul 30, 2007 #10


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    Using a portable DMM (ohmmeter) you could test which side is your cathode versus anode. This would be useful if the markings on the diode are ambiguous or you want to double check yourself. Here is a reference, showing how to do this.
  12. Jul 31, 2007 #11
    there is such a concept as diode biasing. forward bias means the positive end of the diode is connected to the positive end of the voltage/current source. in forward bias, current flows. while the reverse bias is the opposite. placing them depending on what bias you need is important.
  13. Aug 11, 2007 #12
    Yes,the direction should be such that n to p points in the direction of flow of current.
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