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Using a MOSFET driver
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Using a MOSFET driver

by RachelAnne on Mon Sep 27, 2021 10:20 pm

I am trying to control the speed of a 15W DC-motor with operating voltage of 12V using an IRF640 n-channel MOSFET as shown in the picture below but without the pull-down resistor RMS = 10kOhm. Instead of it, I always set the Arduino PWM digital pin to value 0, thus when the motor should turn off the MOSFET gets 0V at its gate.
Please see the attachment.


I am trying to control the speed of a 15W DC-motor with operating voltage of 12V using an IRF640 n-channel MOSFET as shown in the picture below but without the pull-down resistor RMS = 10kOhm. Instead of it, I always set the Arduino PWM digital pin to value 0, thus when the motor should turn off the MOSFET gets 0V at its gate.

: DC motor driven by MOSFET :

The problem I face is that even with the maximum value of PWM (255) I don't get the motor to rotate as fast as it does when it's plugged directly into 12V. I get that there is a voltage drop in the MOSFET, but the speed should not drop as much as half of its normally is.

Can the absence of the pull-down resistor Rms 10kOhm case this effect?

Do I need to use a MOSFET gate driver in order to achieve better performance of the DC-motor? (The maximum power the motor uses during operation is not higher than 18 W) If yes, what MOSFET gate driver should I use in this case or should I transfer the MOSFET to IRF740?
Here is the Datasheet between irf640 and irf740
Arduino pins work with voltages 0V - 5V and maximum current that can pass trough them is 20 mA.
Attachments
YFSbM.png
YFSbM.png (18.75 KiB) Viewed 29 times

RachelAnne
 
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Re: Using a MOSFET driver

by adafruit_support_bill on Tue Sep 28, 2021 6:13 am

Like most power MOSFETs the IRF640 (and IRF740) require a fairly high gate voltage to fully turn on. The Rds(on) spec and all the test circuits for both assumes a Vgs of 10v.

A better choice would be a device like the IRLB8721. These are optimized for logic-level gate voltages and achieve a very low Rds(on) by 4.5v. https://cdn-shop.adafruit.com/datasheet ... 721pbf.pdf

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