Choose MOSFET for stepper motor driver

Thread Starter


Joined Nov 25, 2010
In case of being misunderstood, by source I don't mean the source of the MOSFET but the Voltage applied on the left of the schematic, from the drain ti the ground.


Joined Jul 17, 2007
Without knowing what your Vdss specification will be, making a decent recommendation will be very difficult.

You say 4.7v; is that the gate control voltage that's available? All logic-level MOSFETs will work with that.

Is the stepper motor bipolar, unipolar, or actually a BLDC motor? Posting the manufacturer and part number or a link to the datasheet will be most helpful.

Thread Starter


Joined Nov 25, 2010
Each phase of the motor should be carrying 1,8A through its resistance (2,6 Ohms), so the voltage across its coil should be 1,8 X 2,6 = 4,7V. The supply voltage of the circuit should be 4,7 + Vds (drain to source). We would prefer Vds to be smaller than 4,7 in order for the MOSFET to be less consuming. A clip from the motor's datasheet has been attached with a connection circuit. The circuit won't be the same, instead of transistors we are going to use MOSFETs. The motor's maximum speed won't be more than 1000 steps/sec.
Any ideas about which MOSFET to choose?



Joined Feb 19, 2009
For "As Small As Possible" - SI5406CDC

20V Vds
6A continual current
1.5V Vth turn on, so 4V would switch it well.
6Watts dissipation - Mount on large copper pad for heat sinking.

Size is 2mm x 3mm, smaller ones are available, but would require reflow soldering as they are in a BGA type package.