MOSFET(metal oxide field effect transistor) please can you tell me why all of mine are short-circuit?They are new!

i have bought 2 mosfets (irf z44v and irf 540) and the drain is live even when the gate is not connected to anything or 0v?

too much power or current
Plasmana8 years ago
MOSFET's works differently from transistors. A transistor needs current flowing into (or out) of the base to 'turn on'. A MOSFET needs a small voltage charge at the gate to 'turn on', the gate holds the charge like if it is a capacitor. That is why they stay on when the gate is not connected to anything. I suggest putting a 10k resistor between the gate and the source of the MOSFET to drain the charge from the gate.
12V (author)  Plasmana8 years ago
i have just tried this but made no difference.. have you ever had problems with one of two(meaning i may have a bad one)? when i first tried it i connected the gate to the source voltage has this burned it out also how static sensitive are they? also is it energized when the gate is - or+?
AndyGadget8 years ago
How are you testing them? The IRF540 has a diode (cathode to drain, anode to source) across it. If you're using a multimeter low resistance check it may well be seeing this. (If you reverse the connections it should be high res with the gate at 0V.)