I need to drive an IRF630 (power N-channel MOSFET) from Arduino. I know this MOSFET requires a VGS of 10V to fully turn on BUT for my application I can work with 5V (I’ve tested it) and the power loss incurred is very minimal (it is almost fully on at 5V and my currents do not exceed 1Amp). Anyway, my question is this: With reference to the attached figures, would you prefer option A or B to drive the gate from the digital output of the Arduino ? Rser is there to limit any transient current and hence protect the digital port and Rpull is there to tie the gate to ground to avoid damage or the MOSFET from switching on when the gate is open circuited (if ever). Anyway, speed is not an issue here so I can live with Rser. My argument is: In option A the gate voltage would be a little less than 5V (because of the potential divider formed by the two resistors). I though of option B to solve the problem (I know it is a minor one in practice). But I am curious: would option B serve the same purpose better ? Thanks in advance.
If you will be driving high currents with your IRF630, I would recommend using a buffer between the arduino and the powerfet. Otherwise the current spikes will introduce problems at the arduino site.
@ joop: Thanks for the reply. As I said, I won't be driving any heavy loads. Only switching an array of LEDs that total to a maximum of 1Amp. No inductive switching etc. That's why I'm positive that I do not need to include buffers etc. What is your opinion on Option A or option B as gate drive ?
It won’t matter much.
You say 1 Amp is not a heavy load, personally I would start worrying if the load is close to the arduino board. If not, then you could be safe.
You are right, option B is slightly better because option A slightly reduces the gate voltage, and you are driving the mosfet with a marginal gate voltage anyway.
I would reduce the series resistor to 220 ohm, especially if you are using PWM.
@ dc42: Thanks for your reply. That's it, with 5V the IRF630 is just ON, so I'm trying to save every mV of gate drive :-) I am not using PWM or any fast switching. Just switching the LED array ON and OFF with seconds or minutes in between, so switching speed is not an issue here, but the 1kOhm series resistor can even go down to 470Ohms and still have the Arduino channel protected for transient currents due to the parasitic gate-drain capacitance. Of course, using a buffer IC would solve all these issues, but why complicate the circuit and incur extra costs when this simple gate-drive works well for the current application? @all: Any comments?
Exactly. You only need to use a driver IC if you are switching the mosfet at high frequency, so for your application just drive the gate from the Arduino. That is what I do. For switching low voltages at low speeds, you can even do away with the series resistor.
dc42: Exactly. You only need to use a driver IC if you are switching the mosfet at high frequency, so for your application just drive the gate from the Arduino. That is what I do. For switching low voltages at low speeds, you can even do away with the series resistor.
One might also need to use mosfet gate driver IC for high power mosfets that are switching higher current loads even at slower PWM rates. The larger mosfets have significant gate capacitance so high current drivers can help the mosfets charge and discharge the gate capacitance faster, thus keeping the switching transition time shorter, which helps with the heat/power dissapation of the mosfet. The pretty high output pin current ratings of an arduino output pin works pretty well with most mosfet switching applications, however when talking really large current switching loads using large mosfets or mosfets wired in parallel, the purpose designed gate driver IC are almost always recommended.