Assistance needed to choose resistor for project

[Goku]

Hi all,

I'm a newbie to this forum. Please forgive me how much ever dumb or non technical my queries may be.

I'm doing a project in power electronics where I'm using a resistor across drain of a MOSFET.

The Voltage I'm using across the drain is 20 V and resistor I'm using is 100 ohm,2 W. Required wattage as per the calculation V*V/R = 4W .The resistor I've used blows up when my duty cycle is 99%.

Is it necessary to use 4W resister or lesser so that it does not get blown up?

Is it safe to use resisters higher or lower watt resisters for this connection.

You kind advice would be much appreciated.

[Richard]

The resistor wattage rating is the maximum that it will dissipate without burning out. Dissipating 4W in a resistor only rated for 2W or less is asking for trouble! Use at least a 5W one, or possibly even higher rated if the 5W one gets uncomfortably hot.