Say I have a design that switches a 5A coil using a MOSFET. In order to protect the MOSFET, I place a flyback diode parallel over the coil.
If the coil is switched off, a back EMF current will flow through the flyback diode. I can imagine that a flyback diode can have a smaller maximum current rating because the back EMF current doesn't last that long.
What I would like to know:
- Will the back EMF current be 5A, more or less?
- How long does the current flow through the diode on average before it dies out? I can imagine this is depends on the properties of both coil and diode, but can there be said something about this?
- Is there a rule or calculation to pick a proper maximum current value for a flyback diode?
- What type of diode could you use best as a flyback diode if the goal is to get the smallest PCB footprint?