I have an IRF530 n-channel MOSFET with me which I intend to use to control speed of a 450mA motor from my AVR controller. The controller can either be that can either run at 5V or 3.3V. I intend to PWM the voltage at the gate of MOSFET to see how the speed of motor reacts to that.
But before doing that just to do a sanity check I hooked up the power supply module to my breadboard that supplies both 5V and 3.3V. I checked the current rating of the power supply module and it said it can deliver up to 700mA of current. So the power from rail (5V) goes to motor, from there it goes to my multimeter and then at the drain of the MOSFET. The source of the MOSFET was connected to Ground. I then gave a stable 5V to the gate of the MOSFET. The current flow stabilized at around 280mA. I then changed the voltage at the gate to 3.3V (drain to source voltage stayed at 5V). The current flow stabilized at 240mA this time. If I remove the MOSFET and just directly connect the motor to the power supply, the current flow stabilized somewhere around 360mA.
Now I have this question: 1. When the supply is capable of delivering up to 700mA why just ~300mA flow through? The power supply module is fed by a wall wart adapter which says maximum current of 500mA. But still it could go higher but it didn't? IRL530 datasheet says it can deliver up to 22A of current so the limiting factor shouldn't be the MOSFET. The graph in the IRL530 datasheet says that at 5V gate voltage and 5V drain-source voltage close to 22A should be able to flow through. But I am new to MOSFETs. Is there a connection between the gate voltage and drain-source voltage? What is limiting the current flow here?