Guys i trying to step down voltage using mosfet.
Application:
Input battery supply 40 to 50 volt
Output voltage is 12 volt not more than 500 ma.
Mosfet heating issue due to...
Since the mosfet is dropping voltage 37 volt (50v-13v), if output load consume 500ma. Then power dissipation will be 37*0.5= 18.5 watts. For this reason my mosfet getting too hot.
Can anyone suggest how to reduce the heat or what is the option for stepping down 50v to 12v without using buck converter.
Heat is not the problem. According to other things I've been told on this site, MOSFETs suffer a thermal runaway problem (hot spots on the silicon) when they are used as voltage controlled resistors.
Is it okay to use a MOSFET in its resistive region with a heat sink?
If you use a linear regulator which is made for the purpose, you will avoid the hotspot problem, but will still need a heat sink. However, in my cursory search, I couldn't find anything that could handle 50 V in and which would provide 500 mA output. The LM317 or LM217 might be able to handle it.
If you have your heart set on making a transistor controlled circuit using feedback, you can use a BJT (Darlington?) instead of MOSFET, however I am hesitant to give more specific advice since I'm a little out of the electronics game these days. You will need a heat sink for sure.
If you want to avoid heat, a buck converter is the correct thing. Without that, you're going to be generating heat somewhere.
Sticking a sufficiently chunky wire-wound resistor in series with your circuit would lose some of the heat that would otherwise be generated in the mosfet. Perhaps a 40 ohm resistor, which would drop the 40V to 20V at 500 mA. But the resistor would dissipate up to 10 W.
