im a mechanical engineer and im working on controlling an automotive fan using arduino , mosfet and motor driver .
I know that MOSFET can be used as a switch. When sufficient Vgs is applied, MOSFET will turn on and so the load (fan).
This is my understanding of this circuit, please correct me if I’m wrong or missed anything?
5V PWM is a digital signal and by adjusting the duty cycle, I can control the average value.
For 100% duty cycle Average voltage = 5V For 50% duty cycle Average voltage = 2.5V For 0% duty cycle Average voltage = 0V
So in case if i want to control a duty cycle at 20% the voltage will be around 1 from the micro controller. So is there any Mosfet operate betwwen 1-5 V?
Note: i only need the mosfet to control the signal that goes to the driver ..
Please recommend me a Mosfet .
You are not understanding PWM correctly.
PWM outputs turn on and off at a particular rate. However, the ON and OFF times are variable. Here's an example:
Imagine the PWM is running at 1000 Hz (that is, 1 millisecond or 1000 microseconds PER CYCLE).
Now imagine an imaginary 5 volt light bulb is connected to the PWM pin (forget the driver transistor or MOSFET for now).
If the pin stayed high, the light bulb would be full brilliance. But, to control is we use PWM...
Imagine the PWM pin is ON for 250 microseconds and OFF for 750 microseconds. The total cycle time is still 1000 Hz, but the pin in on only 25% of the time. Therefore, the bulb will be at 25% brightness (because the filament cannot possibly follow the on/off cycles... it "thermally integrates" the PWM input).
Now, let's set the PWM to 800 microseconds ON and 200 microseconds OFF. Again, the cycle time is 1000 Hz, but the average (integrated) power to the bulb is now 80 percent and it's much brighter.
You can go anywhere between 0/1000 (full off) to 1000/0 (full on).
Do you see the beauty of this? In the real world, you will be using a transistor or MOSFET to control a high power load.
If you did it purely analog, (say, 50 percent power), the load would get 50% and the MOSFET would burn off, as wasted heat, the other 50%, requiring a larger MOSFET (more $$$) and a big heatsink (more $$$ and more board space wasted).
But with PWM, the switching device (MOSFET, etc..) is either fully ON (virtually no voltage drop across it = minimal power lost) or it's fully OFF (again, open circuit draws no current = no power loss).
SO, with a relatively small MOSFET you can PWM control a large load and waste almost no power (i.e. the MOSFET stays cool).
Other devices can also be controlled the same way. A DC motor mechanically integrates the PWM pulses and spins smoothly.
An LED will follow the PWM and actually be blinking, but at 1000 Hz your own eyes cannot see the flicker and you VISUALLY integrate the average brightness value.
Lastly, there is an optimal PWM frequency for each use. A very high PWM frequency could, for example, be very inefficient driving a DC PM motor due to the high frequency being "lost" in the motor inductance.
A very low frequency might make an LED visibly blink, or a DC motor actually "cog" (speed up and slow down as it follows the slow on/off cycles).
A very high frequency can also waste energy in driving the gate of the MOSFET, so you see the PWM frequency is a compromise between two conflicting goals, and you have to choose the right frequency for each application.
Hope this all didn't overwhelm you... if you have any questions let me know.