Buck-boost converter

Discussion in 'The Projects Forum' started by anoman38, Apr 25, 2012.

  1. anoman38

    Thread Starter New Member

    Dec 28, 2011
    10
    0
    I built a DC-DC buck boost converter. I use IR2184 gate driver to drive IRF3710 MOSFET. I used optocoupler 6n137 past the gate driver for isolation purposes. My problem is that when the duty ratio is less than 0.5 the gate driver signal is so nice and the output voltage is good. But when the duty ratio is increased above 0.5 the gate driver signal get disturbed and take a little time and then get heated and finally destroyed. Can you please help me what is wrong, how can I solve it?!
    Thank you

    gate driver IR2184
    http://www.datasheetcatalog.org/datasheet/irf/ir2184.pdf

    IRF3710 MOSFET
    http://www.irf.com/product-info/datasheets/data/irf3710.pdf
     
  2. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,006
    1,528
    It sounds like your saying you put the opto between the driver and the mosfet? The opto should be between the driver and the converter chip. Post your schematic!
     
  3. anoman38

    Thread Starter New Member

    Dec 28, 2011
    10
    0
    I put the opto between the driver and the PWM generator. The arrangement is ( PWM generator-opto-driver-MOSFET). By the way, this problem appears even if I connect the driver directly to the PWM generator without using opto.
     
  4. wayneh

    Expert

    Sep 9, 2010
    12,100
    3,036
    You need to post your circuit schematic, and please define what you said burned up in your first post. Remember the story of the blind men and the elephant? That's what it's like trying to diagnose a circuit with no schematic.
     
  5. anoman38

    Thread Starter New Member

    Dec 28, 2011
    10
    0
    ok thank you for your replying. Attached to you the schematic diagram. As I discussed above that the driver heated and stop working when the duty ration is 0.5 and higher. This problem appears with or without using optocoupler.
     
  6. wayneh

    Expert

    Sep 9, 2010
    12,100
    3,036
    You've got your MOSFET in the wrong place. The source should be at ground with the inductor above it on the drain.

    That said, I don't think that alone would cause the driver to overheat. Is that a 12Ω resistor on the gate? What frequency is this thing running at? Maybe you're simply over-driving it beyond its ratings. That's a pretty big fet.
     
  7. anoman38

    Thread Starter New Member

    Dec 28, 2011
    10
    0
    This is the right buck boost circuit. you are talking about boost converter. My converter is buck-boost converter. The switching frequency is 40KHZ. The resistor of the gate is 12 ohm.
     
    Last edited: Apr 26, 2012
  8. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,006
    1,528
    What is your gate voltage?
     
  9. kelvin_mksinst

    New Member

    Apr 28, 2012
    3
    0
    Which part is damaged? The FET or Driver?

    What is the value of the inductor? What is the power rating of your buck-boost converter? Is there possibility that the inductor got saturate? If the inductor saturates, current can ramp dramatically to fail the FET.
     
  10. anoman38

    Thread Starter New Member

    Dec 28, 2011
    10
    0
    I used 1mH inducor. you can find the link below to see the inductor type. the driver is damaged when the duty cycle is increased above 0.5.
    As stated in the datasheet of the inductor that the inductor is saturated at a current equals 5 times the maximum inductor current which is 25A. the maximum current flowing in the inductor in my circuit is 15A. the power rating of the inductor is 120W.

    Attached to you the type of the inductor used
    http://www.coilws.com/images/HF5712-561M-25AH-Cust-Rev A.pdf
     
Loading...