Methods Of Converting Ac to Dc

Discussion in 'General Electronics Chat' started by arthur92710, Mar 19, 2009.

  1. arthur92710

    Thread Starter Active Member

    Jun 25, 2007
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    The only way I know of changing ac to dc is rectification with diodes, But they are only 81% efficient. Transformers are used in power supplies and they also drop some efficiency. How are more efficient power supplies made? Like the new 80 Plus psu's. And what are other ways of efficiently converting AC to DC.
     
  2. DedeHai

    Active Member

    Jan 22, 2009
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    instead of using diodes, which have the forward voltage drop and therefore high losses with big currents, you can use MOSFETs to switch actively. use comparators for example to determine switching points-.
     
  3. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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  4. arthur92710

    Thread Starter Active Member

    Jun 25, 2007
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    Thanks for the quick replies! Ill get to them as soon as I finish reading "Power to the people" (WIRED magazine):)
     
  5. arthur92710

    Thread Starter Active Member

    Jun 25, 2007
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    I have a question. On page 18, figure 19, it says Passive Turn-ON, Passive turn-OFF, what is that?
     
  6. t_n_k

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    Mar 6, 2009
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    Passive Turn-ON means that if you have a low drive signal applied to the controlling input MOSFET's gate the load is on. Passive Turn-OFF case means that with no drive applied to the controlling input MOSFET's gate the load is off.
     
  7. arthur92710

    Thread Starter Active Member

    Jun 25, 2007
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    well that was simple. Thanks alot!
     
  8. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    Simple, but I think it misses the point.

    PASSIVE TURN-ON CIRCUIT
    Ron is a passive component. The turn-on of the output MOSFET is dependent on this resistor. Hence the term passive turn-on. The gate capacitance charges through Ron. If Ron is a high value, the transistor will turn on very slowly.

    PASSIVE TURN-OFF CIRCUIT
    Roff is a passive component. The turn-off of the output MOSFET is dependent on this resistor. Hence the term passive turn-off. The gate capacitance discharges through Roff. If Roff is a high value, the transistor will turn off very slowly.
     
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