# MOSFET max power

Discussion in 'Homework Help' started by ihaveaquestion, May 9, 2009.

1. ### ihaveaquestion Thread Starter Active Member

May 1, 2009
314
0
Could someone please confirm that I approached particularly part B in the right way to find the right answer..

problem:
http://img366.imageshack.us/img366/9329/22112211.jpg

http://img366.imageshack.us/img366/427/778899.jpg

As a side question, power for the MOSFET is P = V^2/Reff but if the Vs isn't connected to ground, i.e. if the circuit is not complete, then no current flows. In the above equation for power, the current i is not in the equation, yet it is still taken into account? In other words, it's implied that if no current flows no power is consumed?

2. ### mik3 Senior Member

Feb 4, 2008
4,846
63
If the current is zero then no power is consumed.

3. ### mik3 Senior Member

Feb 4, 2008
4,846
63
No because even when the MOS is off a tiny current flows through it.

Also, when the MOS is fully on it has a voltage drop across it.

Thus it always consumes some power even if it is very small.

4. ### mik3 Senior Member

Feb 4, 2008
4,846
63
Yes the minimum power is 0 which can be only in theory.

For the last question you can determine the current through and the voltage across the MOS and then multiply them to get the power dissipated.

5. ### ihaveaquestion Thread Starter Active Member

May 1, 2009
314
0
I have more than one mosfet hooked to each other and want to use the V^2/R equation

6. ### mik3 Senior Member

Feb 4, 2008
4,846
63
If you know the off and on resistance of the MOS and the voltage across each one then you can use it.