Why Vds never goes to zero in ltspice simulation in this case? Boost PFC Converter

Discussion in 'The Projects Forum' started by AbhimanyuSingh, May 23, 2011.

  1. AbhimanyuSingh

    Thread Starter New Member

    May 22, 2011
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    Why do Vds never goes to zero...even with a bjt, the same happens. The current through the mosfet follows its equation that depends upon (Vgs-Vth). But the current passing through inductor is very very high as comapred to the mosfet current. Is that the reason..??What should I do then? A boost pfc converter isnt supposed to be like this??
     
  2. CDRIVE

    Senior Member

    Jul 1, 2008
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    In the future just post the image of the schematic. Even those of us with LT Spice installed would rather just view the schematic, instead of downloading your spice.
     
  3. AbhimanyuSingh

    Thread Starter New Member

    May 22, 2011
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    here is the image.
     
  4. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    You need to choose a MOSFET model. The generic NMOS in your schematic is a small geometry device, with very high Rds(on). Right-click on M1 and choose a part with low Rds(on).
     
  5. CDRIVE

    Senior Member

    Jul 1, 2008
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    Are you expecting Rds(on) to equal zero? Absolute zero isn't possible, with any model.
     
  6. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    I originally thought that this was his question, but if you run his sim, probing Vds makes it look as if the transistor is not switching. However, if you probe the drain current, it pulses at 1mA. If you change the model to IRF6635 (or some other BF MOSFET), the drain current pulses reach 190A. Obviously, this is excessive, but I think it illustrates my point.
     
  7. CDRIVE

    Senior Member

    Jul 1, 2008
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    Thanks Ron, that clears it up.;)
     
  8. AbhimanyuSingh

    Thread Starter New Member

    May 22, 2011
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    Thanks Ron and Cdrive...thanks a lot...it works now.
     
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