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Flyback or simple boost converter?

Discussion in 'General Electronics Discussion' started by BlackMelon, Nov 16, 2014.

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  1. BlackMelon

    BlackMelon

    188
    5
    Aug 7, 2012
    Hello,

    I made a boost converter which was programmed with PID feedback loop. When I programmed it to boost 12V, 2.5Ah battery voltage up to 150V, the converter could not do. Even in a no load condition, the maximum voltage that the converter can do is around 107V.

    My desired specification is:
    1) 1mA ripple current / 10mV ripple voltage
    2) 100W maximum power
    3) 200V maximum output voltage

    My plan is to use a flyback transformer to help stepping an output voltage up. After looking on the internet, It says that:
    1) The flyback boost converter is usually use in low power applications.
    2) The flyback boost converter has very high ripple current.
    3) The operating frequency is specify ( I'm willing to spend time to find a suitable switching frequency)
    4) Continuous current mode is not stable

    Which one is more suitable for my specification?

    ref:
    http://www.wcmagnetics.com/images/pdf/wcmappnotes.pdf
    http://www.eetimes.com/author.asp?section_id=183&doc_id=1319222

    Thanks :)
     
  2. BlackMelon

    BlackMelon

    188
    5
    Aug 7, 2012
    My microcontroller is an Arduino UNO. 8bit fast PWM & 10bit analog reader to read an output voltage. The boost converter was operating at 62kHz frequency.
     
  3. BobK

    BobK

    7,682
    1,686
    Jan 5, 2010
    On a normal boost converter (single inductor, not transformer), the breakdown voltage of the switching device has to be higher than the max voltage output since that voltage ends up across the switch (MOSFET or BJT), when the switch is off. What were you using for a switch? What is its breakdown voltage?

    Bob
     
  4. BlackMelon

    BlackMelon

    188
    5
    Aug 7, 2012
    The switching component is a MOSFET R6004ENX. Its Vds(max) is 600V. Dissipation power (Pd) is 40W. Its maximum current is 4A. MOSFET's reverse diode dv/dt is 15V/ns.
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,418
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    Jan 21, 2010
    For a simple boost converter the maximum voltage is also strongly influenced by the turn-off time of the switch. A flyback design allows you to multiply this voltage by the turns ratio.

    For 100W output power, your average current from a 12V source will exceed 8A -- even assuming 100% efficiency. The peak current will be at least twice this.

    If we assume 80% efficiency, and the input voltage sagging to 11V, then the input current will average 11.4A and the peak will be at least 22.8A, and may be as high as 35A.

    A device capable of switching 4A isn't going to cut the mustard.
     
  6. BlackMelon

    BlackMelon

    188
    5
    Aug 7, 2012
    I understand that 100W and 12V will draw current around 8A but I've calculated with an inductor voltage-current relation.
    I find that the voltage does not ramp up to 8A. Could you please look at the attachment and tell me that my calculation is valid or not?

    Thanks :)
     

    Attached Files:

  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    If it doesn't ramp that high then it won't be able to deliver the power you require.
     
  8. BlackMelon

    BlackMelon

    188
    5
    Aug 7, 2012
    Is this the reason why my converter can't step output voltage up to be higher than 107V? Will reducing an inductance be a good solution to make it ramp up higher?
     
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,418
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    Jan 21, 2010
    it may be. It will certainly limit the power available. Turn off time will affect the maximum voltage available.

    Do the calculations :)

    You can also try reducing the frequency.
     
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