component-selectioncomponentsmosfetwiring
Im new to use of mosfets.
If I was to use two Mosfets with an Arduino, would I be able to drive them both with just one digital pin connected to both mosfet's gates but opposite actions?
For example: Digital pin 2 goes High, Mosfet-1 opens a circuit, Mosfet-2 closes a circuit… and vice versa.
I'm currently using n-channel mosfets but I read about p-channel. Having p & n gates tied to one pin?
If the gate is truly connected to a terminal block, it is vulnerable and needs to be protected. A series resistor and TVS diode would be my first stop at protecting it.
simulate this circuit – Schematic created using CircuitLab
A cap in parallel with the TVS will help slow the ESD event down, if you can afford the added capacitance on the gate, and give the TVS a little more time to turn on. Make sure the traces are short as possible and the TVS has a solid ground connection. A regular Zener diode is just too slow for ESD protection. It's better than nothing, but at that point, your primary means of protection will be the MOSFET's internal clamp, if it has one.
Your problem is the gate drive voltage. If you look at the datasheet for the STP16NF06, you'll see that the 0.08 Ω Rdson only applies for Vgs = 10 V, and you're driving it with only (a bit under) 5 V, so the resistance is much higher.
Specifically, we can look at Figure 6 (Transfer Characteristics), which shows the behavior as Vgs varies. At Vgs = 4.75 V and Vds = 15 V, Id = 6 A, so Rds = 15 V / 6 A = 2.5 Ω. (It may not actually be quite that bad, due to some nonlinearities, but it's still more than you can tolerate
ESD could also be a problem: the gates of MOSFETs are very sensitive, and there's no reason that the Arduino (whose microcontroller has ESD protection diodes) would also necessarily be affected.
I'd suggest getting a MOSFET with a low enough threshold voltage to be fully on at 4.5 V. You can even get MOSFETs that incorporate ESD protection on their gate.
Best Answer
The answer to your question is, yes sometimes.
Provided the P-Channel device is connected to the same rail as the MCU, you can use a circuit like below quite happily.
simulate this circuit – Schematic created using CircuitLab
This circuit turns on either LED depending on the state of the GPIO pin. When LOW M1 will be on and D1 will be lit. When high, M2 will be on and D2 will light.
You do however need to be aware that you are doubling the gate capacitance being driven by the MCU pin and as such turn on and turn off times will be extended in this configuration. The double cap also increases the required gate switching current.
Note each MOSFET should have it's own gate resistor, R1 and R2 here, and those should be sized so the switching current of both added together does not exceed the drive current of the GPIO.
The "default condition resistor", R5, can be a pull down as shown, or a pull up, depending on which LED you want to be on when the MCU is not initialized yet.
Both the P and N MOSFETS need to be chosen to have a maximum Vgs-Threshold around Vcc/2.
NOTE: The MOSFETS will not switch at exactly the same time. As such you should not depend on this circuit to drive a push-pull type load or other circuit that depends on edge coincidence.
If the P-Channel is attached to some higher rail, then you need something more complicated, like Wesley's answer.