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I Output of a half wave rectifier

  1. Nov 14, 2017 at 9:07 PM #1
    In a half wave rectifier only a single diode is present. One end of the secondary wire of the transistor is connected to the p side of diode while the other to the load resistor. The n side is connected to the load resistor. When the diode is reverse biased no current passes through it. But current does pass through the other wire of the secondary which eventually meets the load transistor. So wouldn't the output in this case be an ac current?
     
  2. jcsd
  3. Nov 14, 2017 at 9:18 PM #2

    davenn

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    hi there

    just a few wrong words in there :wink:

    "One end of the secondary wire of the transistor is connected......." should be One end of the secondary wire of the transformer is connected.......

    "But current does pass through the other wire of the secondary which eventually meets the load transistor."

    should be ..... But current does pass through the other wire of the secondary which eventually meets the load resistor.

    well it's a pulsed AC .... have you looked online to see what the waveform looks like ?

    Voltage-Supply-in-Half-Wave-Transformer.jpg

    the top is the full AC voltage on the secondary side of the transformer
    the lower is the half wave rectified voltage across the load resistor after the diode

    half-wave rectification in general uses larger value smoothing capacitors to help keep the voltage from sagging (dropping) so much between each pulse.

    half-wave rectification is also generally only used where the equipment isn't sensitive to lots of AC ripple voltage



    Dave
     
  4. Nov 14, 2017 at 9:23 PM #3
    thanks for correcting me... m new at this so i mixed up all the terms... i know that the graph of the half wave rectifier looks that way.... but my point is the diode less wire of the secondary will conduct current no matter what happens... so why didnt the graph consider thqt
     
  5. Nov 14, 2017 at 9:26 PM #4

    davenn

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    no it doesn't, there is only current flowing in one direction, and that is the 1/2 cycle when the diode is conducting
    NO current is flowing during the other 1/2 cycle
     
  6. Nov 14, 2017 at 9:27 PM #5

    phinds

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    And just where is that current going to come from?
     
  7. Nov 14, 2017 at 9:27 PM #6
    No current is flowing through the DIODE. But current should flow from the other wire
     
  8. Nov 14, 2017 at 9:28 PM #7
    from the secondary transformer due to mutual induction
     
  9. Nov 14, 2017 at 9:36 PM #8

    davenn

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    no ... why would you say that ? there is a hole in the circuit and for current to flow, there needs to be a complete circuit

    no :smile:

    Dave
     
  10. Nov 14, 2017 at 9:37 PM #9
    why is there a hole in the circuit
     
  11. Nov 14, 2017 at 9:43 PM #10

    davenn

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    you have already answered that yourself


    because the diode is reversed biased and call it a hole in the circuit or maybe a closed door
    whichever description, no current is flowing through it in the other 1/2 cycle, therefore no current flows anywhere in the circuit during that 1/2 cycle
     
  12. Nov 14, 2017 at 9:44 PM #11
    ohh... i got it... i was being so stupid
     
  13. Nov 14, 2017 at 9:46 PM #12

    davenn

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    no, never say that of yourself .... never put yourself down like that :smile:
    it was just a small lack of understanding

    Dave
     
  14. Nov 14, 2017 at 9:48 PM #13
    but when the circuit is complete the diode wire has a pulsating current while the other wire has an ac current. Wouldnt that make things messy at the load resistor
     
  15. Nov 14, 2017 at 9:53 PM #14

    davenn

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    when the diode conducts ( and it conducts in ONE DIRECTION only), there is current flowing in one direction only. so the load resistor sees just that pulsed voltage across it
     
  16. Nov 14, 2017 at 9:55 PM #15
    i mean the other wire.... during forward bias circuit is complete. Current naturally flows through the other wire
     
  17. Nov 14, 2017 at 9:58 PM #16

    cnh1995

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    What "other" wire? Do you mean transformer primary?
     
  18. Nov 14, 2017 at 9:59 PM #17
    no the other wire coming from the secondary and directly meeting the load transistor
     
  19. Nov 14, 2017 at 10:05 PM #18

    cnh1995

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    There's no transistor. I assume you mean transformer again.
    This is the circuit we're talking about.
    images.png
    So what is your exact question here?
     
  20. Nov 14, 2017 at 10:10 PM #19
    lets consider the wire connected to diode A and the wire connected to the load resistor B. When forward bias occurs then current flows through A and B. A due to the diode has an output current in the form of pulses. But B has no diode therefore the current would be ac through it. Both of them will pass through the load transistor. I am saying that the output would be quite messy then
     
  21. Nov 14, 2017 at 10:22 PM #20

    davenn

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    no, you are still not quite understanding :smile:

    look at cnh1995's circuit ....

    images-png.png

    and what I said in my previous post

    during the positive 1/2 cycle, when the diode conducts, it ONLY CONDUCTS in one direction ( we will use conventional current flow), in the above circuit that is out of the top of the transformer secondary, where the red + is through the diode, through the load resistor through the bottom wire and back into the transformer

    during the other 1/2 cycle (the negative 1/2) there is no conduction, the diode door is shut
    so current cannot flow into the bottom wire through the resistor and up to the diode.
    there has to be a complete circuit path for the current to flow

    so again repeating what I said earlier, the load resistor ONLY sees current flowing through it in one direction
    and it see only pulses of voltage as the diode conducts for each positive 1/2 cycle


    Dave
     
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