No, logic level mosfet is just a mosfet with a lower gate threshold and gate saturation voltage values. It works the same
as a normal mosfet, just with lower gate voltage values, making it easier to interface directly to 5vdc logic
level voltage values. Both normal and logic level mosfets do not have internal series resistors. I said
many recommend using such a series gate resistor to limit gate current, it doesn't matter which kind of mosfet.
If I were to control the gate of a common mosfet (not logic level, I can't find any ic locally) using the output pin of Arduino, can I be sure that it will output 5v? If so, then I can put a fixed resistor value, without computation? A 2k ohm will do, like you said, is this enough? Or I need to compute according to westfw?
Yes, however a logic level mosfet can be used for both linear and switching mode, just like a normal mosfet but
requiring less gate voltage for any given operation mode.
Very well explained, thanks.
On your soft-start drawing. Yes if you disconnect the top of the 47k ohm resistor and wire it instead to an Arduino output pin, along with a common ground wire from the arduino to common ground from the 6 volt source, it should work in principle. Keep in mind this circuit may be designed specifically with the current requirements for the specific motor used, that is the 0R5 resistor and the 100ufd cap and the 47k may have to be adjusted to work with a motor with a different winding resistance. Also keep in mind this circuit will also act like a soft-stop circuit in the turn off will be as slow as turn-on until the cap discharges below gate threshold value, keep that in mind for any possible safety concerns.
The vacuum pump we will use is 12V, but I can't be sure about its current requirement. What is the common current requirement of pumps at 12V? How can I compute the series resistor and capacitance to be used for gate control, as well as the bypass resistor? Can you provide a tutorial on this?
Thanks! I have that app note. Really good paper.
Most MOSFETs are designed these days to be used in "switching" applications rather than in their linear region, which means that they want to be either all the way on, or all the way off.
Fully turning On the path will just enable the flow of current from source to drain, right? Do I need to add resistor to limit the current consumed by the pump or not? (battery is 11.1v, pump is 12v; at full charge, battery is 12.4v)
If they are used "in between", the power dissipation will get very high, and you won't get anywhere close to the rated current. The "danger" of a normal MOSFET in a logic application is that the logic control voltage is not enough to turn the MOSFET all the way on, which will leave it in the linear "partially on" region, leading to high power dissipation and ... smoke.
So you mean I don't really need the series resistor to the gate? Since the output voltage of a digital pin is <=5v ?
(Say you have a 24V 10A motor switched by a MOSFET, so you go and pick an IRF6613 rated at 18+A with nothing but PCB as heatsink and 3.4mOhm on resistance (at Vgs = 10V); so at 10A you have a power dissipation of 0.34W (IIR), which is well within specification. But instead you drive it with a logic output that only gets up to 3.6V for some reason, increasing Rdson to 50mOhm (which would normally still be pretty good!) Now your power dissipation is 5W, which is pretty substantial, well above the spec, and likely to result in smoke...)
What should I do? I can't find any logic level mosfet here in the our country. I have bought IRF530N. According to datasheet:
VDSS = 100V
RDS(on) = 90mW (wth!)
ID = 17A (this is the max continuous right?)
ID @ TC = 25°C Continuous Drain Current, VGS @ 10V = 17A (confirms above, but i need 10v at gate?)
PD @TC = 25°C Power Dissipation = 70W (this is the max dissipation the ic can sustain?)
Can someone explain:
VGS(th) Gate Threshold Voltage 2.0 ––– 4.0 V where VDS = VGS, ID = 250μA
According to above, I need to input 10v at gate? If this is so, how would I do that using the digital pin of arduino?