mosfet in Proteus

Discussion in 'General Electronics Chat' started by gisele, Nov 28, 2013.

  1. gisele

    Thread Starter New Member

    Nov 28, 2013
    5
    0
    hi
    im designing a converter to boost a voltage using proteus.
    im using a pulse generator to drive the mosfet,
    but it doesnt work
    n im wondering why n how to make it works ?
    between duty cycle is the key,
    where to adjust the duty cycle?
    is it the pulse width in the pulse generator?
    the attachment is the design of the converter ,
    is there any problems?
    your help would definitely save my day!
    thxQ!
     
  2. absf

    Senior Member

    Dec 29, 2010
    1,493
    372
    I would start by changing the MOSFET to a P-channel type. Not sure about the operating conditions of 2SK133, But I would raise the VSource to 12V unless I am using a logic level mosfet.

    What is the frequency and voltage you applied to the gate?

    Allen
     
  3. gisele

    Thread Starter New Member

    Nov 28, 2013
    5
    0
    hi allen
    is it? bcos as i know should b using a n-type
    n actually the mosfet i pick randomly since there r plenty choices
    n i dono which to choose.. perhaps u can give some advice bout it?=)
    the attachment shown the frequency n voltage i applied to the gate (not sure is it the one u asked)..
    n actually i having problem too to fill in those boxes..
    oh is it possible to trigger the mosfet using PIC? means connect the gate to PIC
    coz actually i need to use pwm as a feedback ..

    hmmm perhaps i should give u the whole idea
    im doing a zeta converter circuit,
    no matter whats the voltage input, the output i hv to get 6V
    so i will need to control the duty cycle according to the formula below
    V0= [D/ (1-D)] [Vin]
    n i will need a feedback control using PIC, pwm coding..
    means that if the input is 1v, it wil feedback and adjust the duty cycle to 0.87 to get 6V as output..

    ahhh ..
    too many problems
    hope u can help
     
    Last edited: Nov 29, 2013
  4. TheComet

    Member

    Mar 11, 2013
    88
    12
    First you say you want to "boost" the voltage, and now you're saying you want to convert 12V to 6V?

    Just use a finished IC. Linear has a good selection of buck regulators: www.linear.com

    The reason why your MOSFET isn't switching is because its source is attached to the supply voltage, but the switching voltage is relative to the source potential. You will need to use a p-Channel mosfet instead.
     
  5. crutschow

    Expert

    Mar 14, 2008
    13,027
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    Please confine your textspeak to your cellphone. :rolleyes:
     
  6. gisele

    Thread Starter New Member

    Nov 28, 2013
    5
    0
    hey comet,
    maybe i shouldn't mention 'boost',
    instead i should say no matter what's the input,
    i need to regulate it to 6v,
    by adjusting the duty cycle.

    and im not sure where to adjust the duty cycle in Proteus.
    is it the pulse width in the pulse generator? (as shown in the second attachment)

    i already change the mosfet to p-channel type,
    but the output is still extremely low, almost zero, is just like no output.
    i wonder how and wonder why
    :confused:

    hey crutschow
    sorry i annoyed u
    i will be more careful ;)
    anyway mind to help? :)
     
  7. absf

    Senior Member

    Dec 29, 2010
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  8. gisele

    Thread Starter New Member

    Nov 28, 2013
    5
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    hi allen
    thank you so much for your effort!
    touching :D
    but then if according to my original setup,
    and according to the formula i mentioned before
    V0= [D/ (1-D)] [Vin]
    suppose if the vin is 12, and the duty cycle 40% (i guess is the one you wrote PW=40%)
    the Vo should be 8V which is step down.
    because that circuit is zeta converter which can step up or step down the voltage by adjusting the duty cycle.
     
  9. absf

    Senior Member

    Dec 29, 2010
    1,493
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    If you connect a scope to the gate and drain of the mosfet then you can see that the mosfet only conducts during the negative phase (i.e. 60% part) as I am using P-Mosfet.

    But even if I substitute 60% into your formula, the answer is still not exactly tally with you answer. I am using 10KHz but you're using 100KHz PWM signal. Other factors in the design are affecting the output voltage...

    Allen
     
    Last edited: Nov 30, 2013
  10. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Going back to your 1st post;
    1) The N- channel MOFFET is installed backwards; the intrinsic body diode would conduct continually causing overheating.
    2) The gate signal must be referenced to the MOSFETs source terminal instead of ground.
     
    absf likes this.
  11. gisele

    Thread Starter New Member

    Nov 28, 2013
    5
    0
    hi allen,
    I have tried the way as shown in the attachment
    but is really weird I cant get the output result as high as yours

    http://forum.allaboutcircuits.com/attachment.php?attachmentid=62055&d=1385772159

    My latest attachment is my actual intention,
    feedback to PIC and by using PWM to adjust the duty cycle to get the desire output.
    I'm not sure is this the correct way to feedback..
    and of course I'm still struggling to get the desire output
    :'(

    hi SgtWookie,
    thanks for the explain.
    but I'm so weak in understanding that:(
     
  12. Jony130

    AAC Fanatic!

    Feb 17, 2009
    3,957
    1,097
    Your circuit won't work because you don't drive PMOS properly
    When your PIC gives logic 0 at RC2 output P-MOS is full ON (Vgs = 12 - 0V = 12V).
    But when PIC gives logic 1 state (5V) the P-MOS shoudl be OFF. But unfortunately P-MOS is still ON because now Vgs voltage equal to Vgs = 12V - 5V = 7V. For sure P-MOS will be full ON.
    To properly diver the P-MOS need to use this type of a driver circuit
    [​IMG]
     
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    Last edited: Dec 2, 2013
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  13. absf

    Senior Member

    Dec 29, 2010
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    Besides what Jony has said about the driving of your MOSFET, you are connecting the output of the inverter directly to your PIC RD2. That is going to fry your PIC when the expected output voltage is there (28.1V).

    Shown us your PWM codes so we might be able to help. :D

    Allen
     
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