# Simple Transistor Circuit ?'s

I'm trying to use a IRFZ44N for a simple switch in a car application. I have limited understanding of solid state electronics and was wondering if someone would be willing to give me some advice? Basically I'm just using this component in place of what I would normally use a relay for but in this application the available current is not enough to drive a relay coil. I'm confused though as to how to wire the IRFZ44N. If it just acts as a switch does that mean a 12v+ to the gate and ground to the drain and source to the relay coil I'm trying to power? Is there a simple explanation of how this device operates? For whatever reason I'm having a hard time wrapping my head around it. Is there a better transistor available for this application? Thanks in advance!

Hi,
How much current? Is 2 mA OK? Many cheap optically-isolated relay boards only need 2mA. See the schematic on this page:

DISCLAIMER: Mentioned stuff from my own shop…

Yes that would actually work Terry but I've been wanting to learn how to use transistors and I already have these so figured I would give it a shot. So I tried a simple circuit. 1k resistor on gate 12v to drain and source to a bulb then bulb to ground. Applied 12v to 1k resistor mosfet stayed on and won't shut off even with voltage removed from gate. What am I missing?

Look at the Q3 and Q4 circuits in the schematic, if you have an N channel MOS FET.
Q8 and Q6 if you have a P channel MOS FET.

Applied 12v to 1k resistor mosfet stayed on and won’t shut off even with voltage removed from gate. What am I missing?

A gate pulldown resistor. Try a 10K from gate to ground

In Q4 the 12v is applied through a 10k resistor to the gate and the transistor closes the ground circuit for the motor and mosfets vary resistance with voltage applied to the gate? What's the purpose of D6? Absorb back emf from the motor?

The 10K turns on the MOS FET when Q5 is turned off.
When Q5 is turned on Q4 MOS FET is turned off.

D6 is the kick back diode for inductive loads.

Spend some time watching this series:

The gate of a MOSFET is a capacitor, it stores charge for a while. You should never operate a MOSFET
under load without something to define the gate voltage(*), hence the pulldown resistor.

(*) If the gate voltage drifts to half-on-half-off territory, typically the MOSFET burns up as it has become a