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Topic: how to select mosfet (Read 77 times) previous topic - next topic



I'm using Arduino Uno to power a "Coreless Brushed DC Motor".
The problem is the motor isn't drawing sufficient Current (mA) through Arduino Uno's Output Pin.

I need an FET or MOSFET to drive this motor by satisfying all of the following parameters:

(1) Gate-Source Voltage (Vth) < 2V
(2) 20 mA < Drain-Source Current (Ids) < Any
(3) Drain-Source Voltage (Vds) - as small as possible

I would appreciate any advise you give, including replacing the FET / MOSFET.

With great Regards

Rohit Kumar
Senior Student of Electrical Engineering
Jaipur, Rajasthan


That is not how one selects a mosfet.

1) You have an Uno which can drive the gate with 4.5 volts, not your stated < 2 volts.

2) You need to state the expected motor load. I doubt it is only 20ma.

3) Vds is determined by the parameter Rds and the load current. You select a device by Rds not Vds.


Oct 12, 2017, 04:47 pm Last Edit: Oct 12, 2017, 04:48 pm by groundFungus
Vth is the voltage at the gate that turns off the MOSFET.


1) You have an Uno which can drive the gate with 4.5 volts, not your stated < 2 volts.
That makes a Vgs(th) of 2V a reasonable number, though anything below 3V would likely do, and switch it on completely at a 5V gate level.

The general purpose IRL540 will do fine (mind that's IRL not IRF, the IRL is a logic level MOSFET and opens fully at 5V). There are more popular ones, search the forum. These also come in easy to handle TO220 packages, and it can handle 30A or so.

Do go for an n-channel MOSFET and wire it low side, or you still may not be able to switch it on.

Indeed you can not drive a motor directly from the pin. Most motors draw way too much current (0.5-5A are quite typical numbers for hobby level). Make sure your power supply can handle the motor, and do proper decoupling (that did me in big time a few days ago with brushless pumps).
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