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I have a low-ohm resistor (7.5 ohms) connected to a MOSFET used for passive charge balancing. It is generating a lot of heat on my PCB. I can apply a duty cycle to the switching which somewhat combats the heating, but slows my charge balancing. If a 50% duty cycle is equivalent to a 2x resistance, would using a 2x resistance resistor (15 ohm) generate the same amount of heat?

cs_eng_516
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    The power resistor must be elevated > 1 cm above board or better yet, clamped to a heatsink. Always derate power max for use in circuit and choose proper ratings to minimize temp rise as a % of 100'C rise for % of power rating (approx). Using L boost pulse charge is more efficient with diode perhaps. – Tony Stewart EE75 Apr 07 '22 at 06:30

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P=V^2/R. Two 15 Ohm resistors will still be an R of 7.5Ohm and will still dissipate the same amount of power between them. They will each dissipate half of the total power but they will dissipate the heat over a larger surface area thereby decreasing the maximum temperature of the resistors.

If they are close together this will likely have minimal impact on solving your problem as having the same amount power transferred from the resistors to the PCB and the other components will cause the PCB & other component temperatures to remain the same.

As a previous user suggested, leaving some airgap beneath the resistor will help in dissipating more heat and lower your PCB temperature. If this is not enough, you can increase the PCB surface area to dissipate more heat, add a heatsink or add active cooling like a fan.

Curzii
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  • I would like to know one single 15 ohm resistor generate less heat that a 7.5 ohm pulsed at 50% duty cycle? – cs_eng_516 Apr 07 '22 at 16:31
  • Yes, a single 15 Ohm resistor will generate less heat when compared to a 7.5 Ohm resistor provided that the voltage across the resistor remains the same and the current is less but your charge balancing circuit might not like it if you increase the size of the resistor. – Curzii Apr 08 '22 at 07:02