Hi there, I have another question for you.
I'm currently working on a project, where I control two motors with two switches. Here is a schematic of the project:
First motor is stronger than second one, it needs to be switched via mosfet. Second motor does not need one. When I press first switch, it opens the mosfet and turns on both motors. But if I press second switch, it should turn on the second motor only, because the first one is in series with reverse-biased schottky diode. I want to use schottky diode for this to minimalize forward voltage drop when running both motors via mosfet.
The design also contains two TVS diodes as flyback diodes, protecting the mosfet, one for each of the motors. Beefier one rated for 1.5kW is next to bigger motor and it should work just fine. The problem - and the reason why I'm here asking you for your help - is with the second, smaller TVS diode.
First off, the second motor should consume around 1-2A at maximum, its likely its even less than that. Schottky diode is forward-biased towards it and is rated for 3A. TVS diode in parallel is rated for 600W, which is probably way too much, but it shouldn't matter that much.
The problem arises when I think about what happens when the second motor is turned off. Magnetic field of that motor collapses, has nowhere to go, so it results in increased voltage. That is the reason why there is a TVS diode after all. But there is also forward-biased schottky with very low forward voltage drop. I'm afraid that when the second motor is turned off, the voltage goes up and flows through the schottky rather than TVS, rendering it useless. In that case, I really have no idea how big that voltage/current spike of the second motor is and if it can fry the schottky diode or even the mosfet itself.
So my question is - is the second TVS diode useless? If so, what can I do to tackle the problem? Or maybe because the magnetic field will always collapse only if the mosfet and switches are turned off, the energy has nowhere to go except for the TVS diode, so it will work just fine?
Thanks in advance for your opinion