# MOSFET inverter power calculation

Discussion in 'Homework Help' started by smrams28, Apr 14, 2013.

1. ### smrams28 Thread Starter New Member

Mar 29, 2013
13
0
Hi. I was working on this problem and could use some help. I have to calculate the power dissipated. My thinking was to find the drain current and then multiply it by the drain voltage to get power but thats not right.

WHAT I DID:

Vdd-Vd = V = 5 - 0.9 = 4.1 V
V/R = I = 4.1V/1.6E3 = .00256 A (drain current)
P = I^2R = (.00256)^2*1.6E3 = .0105 W The inverter circuit above consists of MOSFET and the load resistor, R = 1.6 kOhm. The inverter bias voltage is Vdd = 5 V; the MOSFET threshold voltage is 0.5 V. The gate input voltage is +5V. Under these conditions, the MOSFET drain voltage is Vd = 0.9 V; Assuming that the MOSFET I-Vs are linear at this drain voltage, find the power (in Watts) dissipated in the inverter circuit.

2. ### Jony130 AAC Fanatic!

Feb 17, 2009
4,878
1,368
Yes you right. The power dissipated in the MOSFET is equal to voltage across the MOSFET (drain to source voltage) multiply it by drain current.

But here you calculate power wasted in the resistor not in the MOSFET.
After all, you wrote
"drain current and then multiply it by the drain voltage to get power."
And next you don't follow your own words, and calculate the resistor power. Very strange.