Smoothieboard 1.1 MOSFETs and flyback diodes

I am a bit confused by the flyback diodes. On some smoothieware docs it says that there are already diodes installed for the two small MOSFETs. Other docs state that all small MOSFETs have a diode while again other docs say that a diode is necessary for all MOSFETs.

I have the Smoothieboard 1.1 and there are some diodes already on the board but I don’t now for which MOSFETs they are. Do you have any ideas on this?

just to be sure, show a pic of your board please.

but the basic idea is the small mosfets have flyback diodes, and for the big mosfets (which typically don’t need them), you’d need to solder some in if you needed them there


Thanks @Arthur_Wolf! I attached an image of my smoothieboard and I guess the one marked red are the three diodes for the small MOSFETs. So the on documentation which stated that all small MOSFETs have presoldered diodes is right?
Could you please explain me why the big MOSFETs don’t need diodes? Is it because they can handle the voltage spikes?

the reason the big mosfets don’t have flyback diodes is the loads they typically handle (heating elements: beds, hotends etc) don’t need them, they don’t feed back voltage. the small mosfets might handle fans, solenoids, which do feed back voltage, so they have flyback diodes.
what are you trying to do/control?

It will control a vacuum pump and a solenoid valve so I definitely would need a flyback diode.
My main confusion was about some docs say that only two small MOSFETs have a diode while other states that all have a diode. Since on my board are three diodes near the three small MOSFETs I assume that all small ones have a diode so I don’t need to solder another one to the board, right?

and what’s the current load of each?

the small mosfets all have diodes yes. it’s only the big mosfets for which you need to solder ones in.

The solenoid valve only draws 200mA and the vacuum pump has a current rating of 1.8A. The small MOSFETs can handle up to 3A so it should be fine. Thanks a lot for your help about the diodes!