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Boost converter

Discussion in 'Power Electronics' started by Graeme Kelly, Mar 22, 2018.

  1. Graeme Kelly

    Graeme Kelly

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    0
    Mar 22, 2018
    Hello i have designed a boost converter that works on matlab but i am trying to simulate on multisim before i build it but i can seem to get this working i am looking for some assistance . the boost converter is meant to be boosting 3.75 V to 12.8 V to charge a battery

    my parameters are
    Duty cycle = 73 %
    Switching frequency = 200000
    Inductor= 0.8 x10-4
    capacitor= 370x10-6
    mosfet irf520n

    Any help would be appreciated
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    8,994
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    Nov 17, 2011
    Post a schematic. A list of components alone is worthless.
    And tell us exactly where the trouble lies. "Not working" is way too general.
     
  3. Graeme Kelly

    Graeme Kelly

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    0
    Mar 22, 2018
    i have posted the schematic in this post. I am only getting 4.85 volts , when i was carrying out my duty cycle and components calculation for an output voltage of 12.8 v
     

    Attached Files:

  4. Graeme Kelly

    Graeme Kelly

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    0
    Mar 22, 2018
    Any assistance would be greatly appreciated
     
  5. Harald Kapp

    Harald Kapp Moderator Moderator

    8,994
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    Nov 17, 2011
    How long is your (virtual) simulation time? Has the ciruit reached a stable state?
    What's the 12 V battery V2 doing at the output? Remove it.
    What's the voltage of U1? Is it high enough to completely turn Q1 on and off?
     
  6. duke37

    duke37

    5,171
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    Jan 9, 2011
    Are you running at 20kHz or 200kHz?
    Are you turning on Q1 fully.
     
  7. Graeme Kelly

    Graeme Kelly

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    0
    Mar 22, 2018
    thanks for your response i really appreciate it . The simulation doesn't have a stop time so runs continuously. I put the battery in as i am trying to simulate charging of a battery. when i take the battery out the output voltage goes to 99 volts. i have attached a picture so you can see. V1 is 3.75 volts that is the voltage that i am trying to boost up to 12.8 so i can charge a 12 volt battery.

    I am running it a 20 kHz
     

    Attached Files:

  8. Harald Kapp

    Harald Kapp Moderator Moderator

    8,994
    1,785
    Nov 17, 2011
    That won't work.
    Use a large capacitor instead. It is not going to be the same as a real battery but lets you observe the charging process.
     
  9. Graeme Kelly

    Graeme Kelly

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    0
    Mar 22, 2018
    I have put in a 3x-6F capacitor and it is still giving the same out put voltage . can you suggest anything as i don't know what to try as i have exhausted any ideas i have. i have attached a picture so you can see.

    Thanks again for all your help
     

    Attached Files:

  10. Graeme Kelly

    Graeme Kelly

    14
    0
    Mar 22, 2018
    as i am looking for a output voltage of 12.8 and i seem to be getting 99.412 V

    I have done all the calculation for duty cycle, inductor and capacitor.

    could it be the mosfet i am using ?
     
  11. BobK

    BobK

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    1,612
    Jan 5, 2010
    Change the battery to a resistor that would drop 12.8V at the desired charging current.

    Also, the IRF520 required 10V to turn on completely. What is the voltage of your pulse source? For a real circuit, running off a 3.7V battery you will have to use not just a logic level MOSFET but one with an unusually low threshold voltage.

    Bob
     
  12. BobK

    BobK

    7,542
    1,612
    Jan 5, 2010
    Here is a simulation, using all your parameters, a logic level MOSFET and a 12.8Ω load to simulate approximately 1A of charging current. Looks pretty good to me.

    upload_2018-3-22_14-16-39.png
    Bob
     
    Arouse1973 and Harald Kapp like this.
  13. Graeme Kelly

    Graeme Kelly

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    0
    Mar 22, 2018
    hello bob thanks for your reply . see if i was to build this circuit would i put the 12.8 volt resistor in series with the battery to keep the voltage to 12.8 v ?
     
  14. Graeme Kelly

    Graeme Kelly

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    0
    Mar 22, 2018
    i have put a 12.8 ohm resistor in and i am only getting 9.3 volts. i have attached the picture of the simulation.
     

    Attached Files:

  15. BobK

    BobK

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    Jan 5, 2010
    Did you read what I wrote about the IRF520?

    Bob
     
  16. Alec_t

    Alec_t

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    Jul 7, 2015
    As Bob said, the IRF520 needs about 10V Vgs to turn on fully.
     
  17. Graeme Kelly

    Graeme Kelly

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    Mar 22, 2018
    Just seen it there . Thank you very much for all your help
     
  18. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,152
    2,671
    Jan 21, 2010
    Also, your circuit's output, without load will rise to a high voltage. It will be limited by leakage, breakdown, etc.

    I would have recommended a 12V zener as a simulation load. That way you could estimate the current into the battery.

    Because nothing (other than the battery voltage) will limit the output voltage, this circuit can easily overcharge the battery.
     
  19. duke37

    duke37

    5,171
    700
    Jan 9, 2011
    I am interested in the simulation in #12 by BobK.
    The output overshoots on switch on and eventually settles down. Since a certain level of charge is transferred each time, I would expect the voltage to rise gradually to its final value.

    What is the origin of this apparent oscillation?
     
  20. Graeme Kelly

    Graeme Kelly

    14
    0
    Mar 22, 2018
    Thanks for all your responses i really appreciate them , i have one more question. i need a maximum charge charging current of 1.5 amps for the battery that i am using but on my simulation i am getting a charge current of 3.6 Amps. does anyone have any suggestions ? i have attached a picture of my simulation.

    thanks again for the time
     

    Attached Files:

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