MOSFET as dimmier 12VDC 1.2 Amps

Hi All,
I need some information regarding MOSFET as switch.

Scenario:
I want to make a 12V led strip dimmable which consumes 1200mA. I am using Arduino PWM to control the brightness. I have seen some circuits with P channel MOSFET where its gate is driven by an npn transistor. And also some people suggest to N channel MOSFET. I have some queries regarding these two circuit.

1. If I am using N channel MOSFET, which MOSFET will have Vgs = 5V, and can I give PWM out directly to gate of the N channel MOSFET?

2. If I am using P channel MOSFET why the gate is driven by npn transistor ?

The principle is the same either method, the issue is that you want the MOSFET to act like a perfect switch but to do that you need to raise the gate voltage to a higher voltage than the Arduino output can manage on its own. MOSFETs do not have a sharp turn on when Vgs is 5V, in fact they are notoriously variable in the voltage they START to conduct at. To ensure they turn fully on, you need to raise the gate voltage so it is almost at drain voltage with respect to the source pin. So even if the specification says 5V Vgs and your Arduino manages the full 5V (it probably won't) you might only get a partially conducting MOSFET. Bipolar transistors are current rather than voltage driven and they will typically reach full conduction with only 0.7V or so provided to them. The combination of the two will let you fully drive the npn transistor which in turn will fully drive the MOSFET.

Brian.

There are so-called "logic level" MOSFET which can well work with 5V Vgs.

PMOS switches used with positive supply higher than 5V need a level converter for Vgs, a NPN is one of several solutions.

Thanks for the information. Sir can you suggest me an apt P-channel MOSFET and npn transistor for my application. PWM frequency is 50Khz.

Kindly find the screenshots below, In parctical and also in simulation I am getting perfect brightsness when i give LED supply voltage as 16V. Why is it so ?




I am electronics enthusiast, I have least knowledge in MOSFET switch, by functionality if you can explain me that would be very grateful! Thanks in Advance

The circuit doesn't make sense. PMOS would be used if you have a grounded power supply and want to switch the positive terminal.

I would put the lamp (X2) in the drain of the MOSFET regardless of the type used. NMOS (as shown) would seem most sensible though.
Note that with the NPN driver, the PWM waveform is inverted but that should be easy to fix in software if necessary.

Brian.

Use any as IRFR3711
why
-NMOSFET available in a wider range
- have low Rdson => lower conductivity losses 6.5mOhm
- if you want to control the transistor directly from MCU, you have to use logic version where have low Gate Threshold Voltage. This switch on already at 2.7V.
Connection any as, where R1 is load (LED strip) and gate direct drive MCU 0/3V