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  1. #1

    Why high side mosfets get hot in buck converter?

    Here I am attaching step down buck converter circuit. While testing, mosfets on high side get hot extremely high even for 100W load. Low side has no problem. All mosfets are fixed on very big heat sink. Anyone please help me to overcome this problem?

    Circuit is here

    http://obrazki.elektroda.pl/7457407900_1443432614.jpg

    Components used are as per given in circuit. PWM frequency is 50KHz & max duty is 80%. Gate voltage observed is always >10v.
    Last edited by thahseen.claysy@gmail.com; 28th September 2015 at 10:40.

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  2. #2
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    Re: Why high side mosfets get hot in buck converter?

    You have several output smoothing capacitors. They add up to several thousand uF. It takes many cycles for them to charge. Each cycle draws high current through the mosfets, to charge those output capacitors.

    I believe your output capacitors can be a much lower value, maybe 10 uF each. Anyway they will not gobble such a large amount of current.

    Also, have you tried putting a diode in the low side, which is the simplest version of the buck converter?



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  3. #3
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    Re: Why high side mosfets get hot in buck converter?

    I guess you are stressing IR2110 too much, I would try with only one high side FET connected to IR2110 and this 100W bulb load (eventually 2 high side FET)s.
    IR2110 is rated to +/- 2A and with 6 FETs with 3.74nF of gate capacitance each, makes me think it will not work (sorry I´m too lazy to make the math right now).
    If things work ok with just one high side FET connected (with small load obviously) you will have to choose another gate driver or to provide one gate driver for each pair (HIGH/LOW)
    The low side is not getting warm because the diodes inside the FETs are acting the same way the low side FET will when turned on as BradtheRadlike
    kinda said above.



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    Re: Why high side mosfets get hot in buck converter?

    The highside drivers will never be turned on properly since you need a Vgs higher than the supply voltage to turn them on comletely. you wil have a voltage Vds equal to Vgs threshold over the transistor generating a high power drop when you source a high current through it. You either need to generate a higher voltege for the gate driver. or use P-channel transistor with an inverted drive polarity.



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