OK thanks,
Can someone please explain me what this 1N914 diode between the + and the collector for ?
I've missed it for now but I have other diodes : 1N4007, 1N758A, 1N5402
Can I use them instead ? How can I know if I can / can't ?

You need a diode that can handle one amp or so. It prevents inductive kick in voltage as the motor slows after power is disconnected or between pulses from Pwm. That is, the magnetic field of the motor collapses when power is removed and a voltage is created that can damage other components - so the diode creates a short circuit to the reverse voltage created by the collapsing field. The 1N4007 is fine. Current produced by the collapsing field will not be more than the current drawn by the motor. Typically, way less.

 

You need a diode that can handle one amp or so. It prevents inductive kick in voltage as the motor slows after power is disconnected or between pulses from Pwm. That is, the magnetic field of the motor collapses when power is removed and a voltage is created that can damage other components - so the diode creates a short circuit to the reverse voltage created by the collapsing field. The 1N4007 is fine. Current produced by the collapsing field will not be more than the current drawn by the motor. Typically, way less.

I searched after your explanation and I found this :

highly recomended !

thank you very much for explanation !