I have a confusion about interfacing microcontroller with an inductive load , if for example i have a switch lets say a BJT which is turned on and off through a microntroller pin to turn on an off an inductive load (lets say a motor or relay) i would be needing a free wheeling diode for protection because energy stored in the inductor will try to move current through the circuit but what would I have to do for big currents , use a schottky diode or do i have to use some other component with it ?

  • \$\begingroup\$ what is "big currents" in numbers? \$\endgroup\$
    – PlasmaHH
    Nov 10, 2015 at 9:15
  • \$\begingroup\$ look at ULN2803, in particular the freewheel protection diodes and the ability to parallel channels for more current. If that doesn't suit your needs, come back and tell us in numbers why it doesn't \$\endgroup\$
    – Neil_UK
    Nov 10, 2015 at 9:21

1 Answer 1


In most cases you can use a plain diode that is rated for the current you are switching. Up to 100mA (a small relay or pager motor) an 1N4148 will do, up to 1A an 1N400x.

The purpose of the diode is to dissipate the energy stored in the coil. A sckottky diode has a lower Vdrop, so it will dissipate the energy slower. If you need for instance your relay to fall off quickly, a resistor inseries with your diode, or a zener diode (to ground), or a snubber (R+C) might be a better solution, but that is for advances users.

If you are switching extremely fast (not likely), as schottky diode might still be a better choice because it can switch faster.

  • \$\begingroup\$ Thankyou so much i think snubber will be the solution , i wasnt thinking of schottky in terms of reverse recovery current but because its SiC so it can withstand higher currents but thanks anyways i think you are right that snubber will be effective \$\endgroup\$
    – johnny
    Nov 10, 2015 at 10:02

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