i need to drive a motor thats about 100w @12v with a N channel mosfet. i would prefer not to have to use some gate driver and i want to connect the mosfet gate directly to GPIO of esp8266.
recommendations? thanks
Adafruit : https://www.adafruit.com/product/355
Sparkfun : https://www.sparkfun.com/products/10213
You need two resistors. One to keep the mosfet off during power-on / reset and one to protect the ESP8266 output pin from current peaks.
Do you want to control the speed with a PWM signal ?
How are your electronics skills ? That is a lot of amps, and the GND of the circuit for the motor is connected to the GND of the Arduino.
yes the ground circuit of the motor would be connected to arduino.
i have a 12v 60amp switching power supply that branches off to power multiple different modules through dc-dc step down converters. that same power supply provides power to 12v motors.
pwm is not important and 100 watt would be max and only for 30 seconds. if i have to add a heatsink that's fine. i just want a mosfet that will handle it.
could i double the mosfet and get twice the power? i just want to build my own board to save space. All the prefab boards are too big.
i found these on amazon.
Bridgold 10pcs IRLB8721PBF IRLB8721 N Channel MOSFET Transistor, 30V,62A, TO-220,3-Pin
it says, * Very low RDS (ON) at 4.5V VGS, is this going to be a problem on esp8266. i just want to make sure
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Well given that the ESP8266 uses a 3V3 supply voltage, so that is the maximum output voltage it will supply then yes it is going to be a problem. That link also says it is out of stock.
According to the data sheet it will not work at all, this is the graph that shows you it will not work:-
The closest I have found to a 3V3 FET is the IRLB8743pbf, this is the corresponding diagram from its data sheet :-
Which shows it might just work, but I have not tried it myself.
It is touch and go and I think you would be better off using a driver.
That is a long time from a thermal point of view.
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Is it? I thought it would be that the ground of the motor's power supply would be connected to the motor with the other end of the motor connected to the drain of the FET.
this is why i always end up buying mosfet prefab boards with optocouplers on the gate. i really wish there were more options to choose from. i hate having huge enclosures for big bulky prefab boards. would i be better of just using some TIP120's for this then if 3.3v is a problem? my biggest concern here is space.
EDIT: well i guess tip 120 is not an option if i need 100 watts. i only need 10 amps from one of the eight outputs. i could probably just use one mosfet to drive the gate of the bigger mosfet. the other 7 channels 30 watts max
I think at 8 Amps a TIP120 would melt. Using several in parallel would not work because unlike FETs transistors do not naturally share current. Also at 5A current you drop 4V across the collector - emitter, so at 8A it will be more. At 5A the TIP120 will generate 20W of heat.
Why buy prefabricated boards in the first place? Why not just solder the bits you need with strip board?
Where do 8 outputs come from?
i plan on building 6, 8-channel mosfet boards but i would like them to be as small as possible. it seems like at 3.3v im going to end up needing a gate driver regardless. i have many small transistors but nothing good for more than a couple hundred mA. I need to find out what type of mosfets i'm going to buy and how i'm going to wire them to 3.3v logic with or without gate drivers. What would you do ?
the mosfets would be operating 30w 12v solenoid's or 100 watt pump motors. only 1 pump motor on each of the 8 channel boards
I would use a FET driver chip like a FAN7382.
Or maybe just a 74HCT14 buffer to get the signal up to 5V.
so i could use a level shifter to convert the 3.3v to 5v? if i did this what would be a good mosfet to use?
can you help me understand this datasheet.
it says output current max through vcca is 100ma. it says each channel has 50ma clamp current. Does this mean i could only use 2 of the 8 channels at once?
Well not the ones designed for I2C.
The IRLB8743pbf looks good to me.
I was looking at this one
I need an 8 channel gate driver/ level shift that can run 50ma through all 8 channels at 1 time
How does this mosfet board work without a gate driver?
i wouldn't mind designing my own board similar to this
Yes this looks fine. Although it is bidirectional which you don't need and the output is open drain, so you would need to put a pull up resistor to 5 or 12V depending on the FETs you need.
Well it is out of stock and it doesn't mention what FET it uses. It looks like it is opto isolated and that is being used as a level translator to get enough volts to trigger the FET, so again you need to power it with 5 or 12V.
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You understand that a 100W motor does NOT require a MOSFET rated for 100W, right? 100W at 12V is ~10A, and 10A through a MOSFET with Rdson of 0.1ohm means the MOSFET is only dissipating 10W (and the MOSFETs that have been recommended have Rdson much lower than 0.1 ohm!) (you do have to watch the transients, though. One of the reasons for gate drivers is to make sure the MOSFETs switch on and off fast enough not to spend much time in intermediate regions where Rds is larger, and the chip starts to heat up!)
The OP specified an N-channel MOSFET, and not PWM.
Using an optocoupler to pull the gate directly up to 12 V is probably the simplest approach, permitting the use of a non-logic level FET which is easier to find with a really low RDS(ON).
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