Driving Power N-Channel Mosfet, voltage drop :(

Hey All,

I'm using an Arduino Mega to drive this MOSFET:http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=CA&WT.z_homepage_link=hp_go_button&KeyWords=IPP100N06S3L-04IN-ND&x=0&y=0 The Fet's gate is connected directly to a digital IO pin on the Mega. From looking at the datasheet, there should be no problem driving this Fet from logic-level pin. However, with the Fet's source connected to ground and the IO pin HIGH, I can never get a 5V reading between the +5v supply and the Fet's drain (no other load attached). There is always a voltage drop to around 4.5 volts. Any ideas why this is? I want this Fet to act lik a switch and turn fully on. Any help is greatly appreciated.

The Fet's gate is connected directly to a digital IO pin on the Mega.

Bad idea. That FET gate is like a huge (relatively speaking) capacitor and microcontroller pins don't like sourcing current into huge capacitors as there can be a destructive current spike. I'd put a 100ohm resistor in series with the gate.

What is the voltage at the gate?

I can never get a 5V reading between the +5v supply and the Fet's drain (no other load attached).

Assuming the FET and the Arduino are sharing a common ground correctly, I would assume the strange results you are seeing is because you aren't switching a real load. Try wiring the drain to a real load (6 volt lamp, a 5volt relay coil, etc) and see what you see. The max current ratings for that beast of a MOSFET is impressive.

Lefty

Thanks folks. I'm finding now that I am getting no voltage drop with just the meter. However, my load is a piece of muscle wire connected between +5V and Fet drain with two long pieces of 28AWG test lead wire. When the Fet is activated, the voltage across the drain and +5V supply is 4.35V. I'd like to get rid of this drop so the muscle wire works better. Any suggestions? I'll try replacing the 28AWG wire with thicker...