I have the output of a GPIO of an ST microcontroller which switches high (3.3V) or low (0V).
I want a fan to turn on when the output is high and turn off when it is low.
So I need to apply a simple mosfet (between the gpio and the fan) that switches between the saturation region and the cut-off region (like a switch)
Assuming I use this fan and this mosfet (I know it's not the best choice, but let's assume we're using this), I have some doubts on circuit dimensioning:
1) The chosen mosfet has Vgs(th) = 1.7V ... so it will conduct and turn on the fan if Vgs > 1.7V
Since I have 0V or 3.3V output from the GPIO, can I connect the mosfet directly to the pin? Do I need a resistor or some protection diodes?
Since no current is flowing on the gate, I think the only condition to be met is that any voltage on the input of the pin (i.e. Vgs(th)) does not exceed the maximum breakdown voltage of the pin itself ... right?
If it is true, in this case I don't think it will happen since Vgs(th) << Vgpio tolerant (it should be 3V or 5V)
2) The fan datasheet states that the maximum rated current is 74mA ... this means that my drain current must not exceed that value, is this correct?
But it is not clear to me how I can calculate the drain current flowing when the mosfet conducts in saturation (switch circuit closed).
Once I understand what I have to calculate, I can also definitely add a resistor.
I want a fan to turn on when the output is high and turn off when it is low.
So I need to apply a simple mosfet (between the gpio and the fan) that switches between the saturation region and the cut-off region (like a switch)
Assuming I use this fan and this mosfet (I know it's not the best choice, but let's assume we're using this), I have some doubts on circuit dimensioning:
1) The chosen mosfet has Vgs(th) = 1.7V ... so it will conduct and turn on the fan if Vgs > 1.7V
Since I have 0V or 3.3V output from the GPIO, can I connect the mosfet directly to the pin? Do I need a resistor or some protection diodes?
Since no current is flowing on the gate, I think the only condition to be met is that any voltage on the input of the pin (i.e. Vgs(th)) does not exceed the maximum breakdown voltage of the pin itself ... right?
If it is true, in this case I don't think it will happen since Vgs(th) << Vgpio tolerant (it should be 3V or 5V)
2) The fan datasheet states that the maximum rated current is 74mA ... this means that my drain current must not exceed that value, is this correct?
But it is not clear to me how I can calculate the drain current flowing when the mosfet conducts in saturation (switch circuit closed).
Once I understand what I have to calculate, I can also definitely add a resistor.