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?
Best Answer
filament gets red just slightl + MOSFET starts heating up a lot
This means that the MOSFET is not fully on. The Vgs_max of the IRFP260N is 20 V so you can just feed the +12 V to the gate.
The transistor Q2 is also used in a pretty useless way. Let me propose a different schematic:
simulate this circuit – Schematic created using CircuitLab
If M1 still does not fully turn on, then try replacing R1 by 100 kohm.
You don't need Q2 from your original schematic since there is no need for current amplification. The MOSFET's gate is basically a capacitor, it just takes longer to charge with a small current. But since this is for a lightbulb, it does not matter if charging the gate capacitor takes one second. The lightbulb is just as slow.