Hi guys

Can some one explain why some MOSFETS have their drain currents rated at the range of 100's Amps which i am sure is not possible to achieve because the thing or it's pins will melt.


this is an example http://www.irf.com/product-info/datasheets/data/irf2805.pdf

 

Im not too sure what you mean but it sounds like what you are asking is "Why can a MOSFET conduct that much in theory but not in practice?". The answer is that if you can keep the MOSFET cold enough then it will be able to conduct that much without exploding, melting or vaporizing. Also, you have two types of current, instantaneous and continuous. For a brief unit of time (like 1ms), a transistor could easily conduct up to 100A but continuously (over a long period of time), it can only conduct 100mA due to heating.

 

Also that transistor can dissipate 330W (with a damn good heat sink), so if you use P=I^2 R the R is 4.7m Ohms and I is 100A so the total power dissipated is 47W.

 

Well 175 Amps is not a small load, i don't get the picture here, if you can keep it cold at that temperature it reaches when conducting 175 A, why cant you make it conduct even more current. This sounds like super conductor stuff.

 

Current is dependent on voltage and resistance. If you make the device really cold then yes it should be able to conduct that much. But then again, some device can only operate within a range of temperatures so it can only be made so cold. Plus there are factors such as reverse voltage breakdown so when you try to reach those currents you might break down the depletion zone between the body and the source/drain.

 

Please read this
http://www.mcmanis.com/chuck/robotics/projects/esc2/FET-power.html

 

Where is the schematic?
What is the load? (Motor, Solenoid valve...)