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enter image description hereI'm using an IRF540N power MOSFET in a 12V to 24V DC converter. But the MOSFET getting over heated when its connected to source. Before providing a gate pulse its getting very hot. I have attached the schematic here. And the load is a LED lamp of 15W. Battery capacity is 26Ah,12V battery.

MOSFET is driven from a PWM of 100KHz with the duty cycle of 0.7. But is hetting up more before connecting it to the gate pulse.

What might be the possible reasons? Please help me to improve the design.

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    \$\begingroup\$ Welcome to EE.SE. You have built a buck regulator. What you need is a boost regulator. The MOSFET should be an N-Channel to ground where C2 is. The diode is in the wrong place. Look in the 'Related' column to the right for solutions. \$\endgroup\$
    – user105652
    Commented Mar 19, 2018 at 4:40
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    \$\begingroup\$ @Sparky256 Regarding your 2nd sentence. How did you come to a conclusion that the present schematic is a buck? \$\endgroup\$
    – Nick Alexeev
    Commented Mar 19, 2018 at 4:56
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    \$\begingroup\$ Before providing a gate pulse, you say? Is the gate tied to ground when you're not providing a pulse? If not, then the MOSFET could be partially on, which is what generates heat. \$\endgroup\$
    – Criticizing Israel not allowed
    Commented Mar 19, 2018 at 5:01
  • \$\begingroup\$ @NickAlexeev. In buck regulators the MOSFET is normally in series with the coil and power source. The intent is to lower the source voltage. There could be exceptions, but I have not seen one. Of course L1 and L2 have high values. \$\endgroup\$
    – user105652
    Commented Mar 19, 2018 at 5:19
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    \$\begingroup\$ The immediate problem is probably caused by a floating gate. I suggest the OP try just adding a large resistor, say 10k or 100k from gate to source of MOSFET. This should keep the MOSFET off until the function generator is connected. I am not familiar with this topology and can't comment on it apart from that. \$\endgroup\$
    – user57037
    Commented Mar 31, 2018 at 4:35

2 Answers 2

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mosfet could be partially turned on.Please make sure that gate terminal of mosfet is connected to ground.If you have an oscilloscope/multi meter connect the probes across gate and source of the mosfet and check whether any voltage is present or not. Also you can use 10K pull down resistor in the gate terminal of mosfet.

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    \$\begingroup\$ Ground should turn it off, but a resistor from gate to source would also accomplish that. It may not be desirable to pull the gate all the way to GND during operation. Not sure what the voltage waveform at the source will look like. \$\endgroup\$
    – user57037
    Commented Mar 31, 2018 at 4:37
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The current through L1 (which has no business being there) is causing a lot of current to flow through the MOSFET. Remove L1 and resume your testing.

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