How to choose Mosfet for vibration motor?

[kian79]

Hi all,

I am trying to drive a vibration motor using discrete components. This article provides a good overview of the components needed and it also recommends a few specific part numbers:

https://www.precisionmicrodrives.com/application-notes/ab-001-discrete-driver-circuits-for-vibration-motors

I have a fairly large vibration motor(12mm diameter) with the following specifications:

Rate voltage: 3.7V
No load current: 40mA max
Starting voltage: 1.2V max
Load current: 110mA max
Stall current: 220mA max
Operating Voltage: 2 -5 V

The article recommends a P Channel MOSFET (MGSF1N02LT1G). My question is how do I choose the right MOSFET to use? I don't want to be limited to just this part and I am looking for more (perhaps cheaper) options.

Also, what are the considerations for choosing the right flyback protection diode?

Thanks in advance!

[DaJMasta]

In this case, very many mosfets could be used, in fact, it shows in the article the configuration for using an N channel mosfet in place of a P channel.  There can be many factors to consider, but your application manages to dodge most of them:

You don't need a big one because the total drive current isn't too large
You don't need really high or low voltage switching
With normal PWM signals you don't need to worry about switching speed because they should almost all be fast enough


So you need to pick one that will work with a logic level gate voltage (most small ones are), you need to pick one in a big enough package to be able to dissipate the heat involved (current through times RdsOn at your gate voltage times PWM percentage, then work out die temperature rise using datasheet values), and it has to not be over the current limit... but luckily, that only eliminates the very small signal transistors, as even the SOT-23 package mentioned in the article specifically has ample capacity for heat and current despite being in a small package.  So you can pick one to match another used in your circuit, or one that you have on hand, or one that's real cheap, or one that comes in a package type you prefer to solder... whatever may make a difference.  If you pick up your average N channel or P channel jellybean signal mosfet, it should be able to do the job.

[kian79]

Thanks DaJMasta.

In this case, very many mosfets could be used, in fact, it shows in the article the configuration for using an N channel mosfet in place of a P channel.  There can be many factors to consider, but your application manages to dodge most of them:

You don't need a big one because the total drive current isn't too large
You don't need really high or low voltage switching
With normal PWM signals you don't need to worry about switching speed because they should almost all be fast enough


So you need to pick one that will work with a logic level gate voltage (most small ones are), you need to pick one in a big enough package to be able to dissipate the heat involved (current through times RdsOn at your gate voltage times PWM percentage, then work out die temperature rise using datasheet values), and it has to not be over the current limit... but luckily, that only eliminates the very small signal transistors, as even the SOT-23 package mentioned in the article specifically has ample capacity for heat and current despite being in a small package.  So you can pick one to match another used in your circuit, or one that you have on hand, or one that's real cheap, or one that comes in a package type you prefer to solder... whatever may make a difference.  If you pick up your average N channel or P channel jellybean signal mosfet, it should be able to do the job.

[ebclr]

This 1 dollar board will help you do that

https://pt.aliexpress.com/item/IRF520-drive-module-drive-module-MOS-tube-FET-driver-module-board/32808447943.html?spm=a2g03.search0204.3.157.Yh1TuI&ws_ab_test=searchweb0_0,searchweb201602_1_10152_10065_10151_10068_10344_10345_10342_10343_10340_10341_10540_10307_10060_10155_10154_10056_10055_10054_10539_10538_10537_10059_10536_10534_10533_100031_10099_10338_10103_10102_10052_10053_10142_10107_10050_10051_10173_10084_10083_10080_10082_10081_10110_10111_10112_10113_10114_10312_10313_10314_10078_10079_10073-10173,searchweb201603_2,ppcSwitch_5_ppcChannel&btsid=0e2232c6-aa4e-49af-b2e7-4e2a460d1ce5&algo_expid=378916c8-a7f6-47a3-9ffb-f94721d1032a-21&algo_pvid=378916c8-a7f6-47a3-9ffb-f94721d1032a