Diode voltage drop is 70VDC, why?

Discussion in 'General Electronics Chat' started by Aadrik, Dec 15, 2014.

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  1. Aadrik

    Thread Starter New Member

    Dec 15, 2014
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    So I have been working on electronics for about 8 years now and today I was troubleshooting a rapid charger and I noticed that the diodes that made up the rectifier were all reading 70VDC across them. I have been scratching my head since and can not figure out why this is happening since I have always thought that the voltage across diodes should be about .7 or so. I have included the schematic I was using. I took my voltages across D1 and also D2 - D4 with the same results. Anyone have any idea?
     
  2. JWHassler

    Member

    Sep 25, 2013
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    Do you mean D1,-2,-3,-4? If so, they are AC rectifiers, and will be at .7V (forward drop) half the time and some larger voltage ( reverse voltage, a half sine wave) other half of the time. I guess your meter integrates the half sine to 70 volts
     
  3. Papabravo

    Expert

    Feb 24, 2006
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    L1 is not acting as a transformer, but as a common mode choke. Mains connected devices are inherently unsafe and unsuitable for discussion.
     
  4. Aadrik

    Thread Starter New Member

    Dec 15, 2014
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    The reverse thing makes since to me but why would i be seeing that all the time instead of it going from .7 to 70VDC? Also I did realize that L1 is a choke and not a transformer however where is the rest of that voltage going across R1?
     
  5. wayneh

    Expert

    Sep 9, 2010
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    Because it's happening far too fast for your meter or your eyes to capture.
     
  6. Aadrik

    Thread Starter New Member

    Dec 15, 2014
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    Thanks for all the help. Tomorrow I will be using an O-scope on the whole circuit instead of just a multimeter.
     
  7. bwilliams60

    Active Member

    Nov 18, 2012
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    Do you have a min/max function on your meter? If so, record for a moment and it should show you the high, the low and the average which is what you are probably seeing as 70V
     
  8. MrChips

    Moderator

    Oct 2, 2009
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    AAC forums will not indulge in discussion of any circuit or activity that has the potential to shock, electrocute, harm or otherwise put lives in danger.

    This thread is against the AAC forum rules, Chapter 6, as seen here:

    This can be found in our Terms of Service (ToS)

    Any discussion of power supplies that are not isolated from AC mains will be terminated.
     
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