I'm using MOSFET transistor IRFP260N for switching on and off 12V light bulb. The light bulb is between + of 12V battery and drain of a MOSFET, and a source is on the minus pole of the battery. A voltage between gate and source is pulsating around once a second and I can measure about 5,5V there.
When I'm using 12V 6W bulb circuit works fine - a light bulb is switching on and off, but when I changed the bulb with 12V 21W the bulb doesn't come on (filament gets red just slightly and doesn't switch on completely. Also, MOSFET starts heating up a lot and that was not the case with 6W bulb. Can somebody help me to understand why I can not use MOSFET to control switching of 12V 21W light bulb?