# Max amount of 5V mosfets on PWM

I was reading somewhere that you can fry your arduino by have more then 20v used as outputs. So what if I wanted to drive (10) 5v mosfets?

You can even fry it with 0V outputs. 20V is outside of the admissible maximum ratings. There are ratings for voltage, current temperature and some more subtle ones. Driving FETs is often considered uncritical however you have to be somewhat careful, especially if you drive lots of high powered FETs at high frequency. Basically they are a capacitive load and thus it is possible to exceed the maximum current rating. If you add some resistor between the Arduino and the gates (e.g. 1k) your Arduino will be fine. If you frequency is high enough your FETs might then suffer though.

For driving mosfets you need to be concerned about the maximum current you draw from the output pin. The limit for the atmega328p in the Uno and many other Arduinos is 40mA per pin and 200mA total all pins. Mosfets have a high input capacitance, so to keep the peak current below 40mA when the output changes state, a series resistance of 100 ohms or more is connected between the output pin and the mosfet gate. If you are using an output pin to provide a continuous current for example, to drive a LED), then you should keep the current well below 40mA, for example design for 20mA or 25mA as the maximum.

If you want to drive ten mosfets from one pin, then you should use a 1K or greater series resistor per mosfet. Using a higher series resistor slows down the switching, but unless you are switching very large currents or increasing the PWM frequency from the Arduino usual value (around 500Hz), this should not matter.

OMG I'm an idiot.... I mean amps not volts....

And I would want to use one pin per mosfet. So I would need more pins somehow. Or more arduinos....

You said 10 mosfets, and an Arduino Uno gives you 20 pins. If you need more, you could use shift registers to expand the outputs, but the simplest approach is to use an Arduino Mega.

mcreefer:
OMG I’m an idiot… I mean amps not volts…

I also assume you mean 20mA and not 20A

I plan on using these. https://www.sparkfun.com/products/10213 And 10 was a ballpark. It says the aka gate voltage is compatible with any 3-5V controller. So which arduino and how many could it run? Also in the bildr guide connects the source to the gnd pin on the arduino. Could I ground to something else? I would think that grounding them all to the arduino gnd would be a bad idea.

The datasheet indicates it is compatible with any 5V Arduino, however I wouldn’t use that mosfet with a 3V Arduino unless the load is light, because no maximum Rds(on) figure is given for Vgs=3V.

mcreefer: Also in the bildr guide connects the source to the gnd pin on the arduino. Could I ground to something else? I would think that grounding them all to the arduino gnd would be a bad idea.

The current limitations on the I/O pins are because of their direct connection to the microprocessor IC chip. The GND pins on stock Arduinos don't have this concern because while the ground loop is connected to the microprocessor IC, it's also connected to the ground of the power supply (which the current should be flowing to, not the IC). Technically there is a maximum current limit for a female header pin, but it's rather unlikely you'd exceed it with many Arduino projects. ;)

Arduino Pin Current details on http://arduinoinfo.info http://arduino-info.wikispaces.com/ArduinoPinCurrent

mcreefer: Also in the bildr guide connects the source to the gnd pin on the arduino. Could I ground to something else? I would think that grounding them all to the arduino gnd would be a bad idea.

The tutorial is just showing that the external power supply (0-60V) is connecting its ground with the Arduino's. Whenever you use multiple power supplies the grounds must be connected so everybody agrees on what 0V is. If you're only using a single power supply then this is not necessary.

Chagrin:

mcreefer: Also in the bildr guide connects the source to the gnd pin on the arduino. Could I ground to something else? I would think that grounding them all to the arduino gnd would be a bad idea.

The tutorial is just showing that the external power supply (0-60V) is connecting its ground with the Arduino's. Whenever you use multiple power supplies the grounds must be connected so everybody agrees on what 0V is. If you're only using a single power supply then this is not necessary.

Good point. I'll be using one driver for all the leds. Each led is 5-10W so they pack a punch. Also (2) 20W leds.