How many amperes can pass through drain-source of a FQPF9N50C if 3.3v are applied to gate-source?
A FET is controlled by the gate voltage, Vgs (Voltage gate-source). The datasheet always contains these graphs explaining the relation of Vgs to drain current, Id.


With 3.3 Vgs it conducts nothing at 25C if you must believe the Vgs/Id graph.


But, this FET can do 1A@12V at 4.5V Vgs according to the lowest line in this graph.

You need at least 5 Vgs to switch this FET, all other specifications in the datasheet use 10 Vgs, so that would be the recommended value.

In short: you need more then 3.3V to switch this FET. If you do not have more, acquire a logic level FET. (eg: FDP5800)