zeners and capacitor

Discussion in 'Homework Help' started by fran1942, Aug 22, 2010.

  1. fran1942

    Thread Starter Member

    Jul 26, 2010
    58
    0
    Hello, can you please tell me:

    - if I have two 9V zeners in parallel, but with the anode of one connected to the cathode of the other, will they produce a symmetrical +-9V or +-9.7V breakdown device ?

    - when doubling the size of a filter capacitor in a power supply, does it double the ripple frequency or increase the peak diode current ?

    Thanks kindly for any help with these two questions.
    I a pretty sure I know the answers, but just not 100%.
     
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    I believe you will need to put a standard diode or better yet a schottky diode in series with each of the zeners for the parallel arrangement to work properly.

    hgmjr
     
  3. tom66

    Senior Member

    May 9, 2009
    2,613
    214
    You can place two zener diodes in inverse series to produce a ±(Vbr + 0.7V) breakdown voltage.
     
  4. fran1942

    Thread Starter Member

    Jul 26, 2010
    58
    0
    thanks but I just need to know what I would get with two 9V zeners in parallel, both in opposite directions.
     
  5. Potato Pudding

    Well-Known Member

    Jun 11, 2010
    684
    92
    .7 Volts for antiparallel zeners.

    Bigger Filter cap increases Peak Diode current and REDUCES ripple amplitude, and if it causes any change in ripple frequency it would be to lower it.
     
  6. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    Agree with most of that - but why would the ripple frequency change with an unchanged rectifier circuit configuration and an assumed constant supply frequency?
     
  7. Potato Pudding

    Well-Known Member

    Jun 11, 2010
    684
    92
    The 120 Hz Ripple from a basic Mains > Transformer > Full wave rectifier > Filter = No change.

    Some switching supplies you might see a change in their frequency and ripple with a different filter cap and it would tend to lower the frequency most of the time.

    I did say it was and if. ;)
     
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