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I am developing project of MOSFET switch that is going to be used as power switch device in application with 12S li ion battery. To keep power wastes in the minimum level, I have to provide the lowest possible RDSon value. In that application, the maximum voltage of battery will be at the level of 50.4V, so I've decided to use 60V MOSFETs. I really dont want to use 80V ones, as we know, the higher VDS breakdown voltage is - the more RDSon the MOSFET will have. But I am not sure, if this MOSFET will sustain any unpredicted, induced peaks of voltage (there is also BLDC motor on that power rail).

My question: Am I able to protect this 60V MOSFETs from unpredicted, induced overvoltage breakdown peaks?

Edit: Okay, I will ask in another way - Am I able to specify the value of overvoltage peaks from BLDC motor when I am disconnecting circuit in, lets say, 200A of load? Is the BLDC motor driver protected from that kind of problem - disconnecting power in full load?

Edit: Pseude electrical schematic: enter image description here

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  • \$\begingroup\$ Probably not. If a motor is involved, highly probably not, as there are several ways of getting voltage spikes on the DC bus from a motor. \$\endgroup\$
    – user16324
    Dec 21, 2020 at 22:43
  • \$\begingroup\$ So would you advise to change this MOSFETs (quantity of 5) to another with 80V+ breakdown voltage or it is not neccessary? \$\endgroup\$
    – Bratw
    Dec 21, 2020 at 22:51
  • \$\begingroup\$ Power switches when on and conducting do not experience voltage spikes from the BLDC. The only time it might experience such a spike from the BLDC motor is if you used the power switch to cut power to the motor instead of having the BLDC cut the power off first. \$\endgroup\$
    – DKNguyen
    Dec 21, 2020 at 23:02
  • \$\begingroup\$ This power switch in most cases will be triggered firstly as a protection mechanism, and there may be situation of cutting power while BLDC driver is on full-load state. \$\endgroup\$
    – Bratw
    Dec 21, 2020 at 23:15
  • \$\begingroup\$ "disconnecting power in full load?" - why would you want to do that? \$\endgroup\$
    – Bruce Abbott
    Dec 22, 2020 at 9:30

1 Answer 1

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The following circuit should work at interrupting the BLDC load and mitigating the overvoltage spike. When interrupting the load a voltage spike will typically occur due to the stray inductance between the supply and load, e.g. in the wiring. (Inductances do not like abrupt changes in current). In the circuit below, a voltage spike higher than 63V + Vgs_th (the threshold voltage of the MOSFET) will turn on the MOSFET, conducting the energy in the spike to the negative terminal and thus eliminating the overvoltage spike. You can use a standard zener diode since the MOSFET absorbs virtually all the energy.

A transient voltage suppression (TVS) diode connected directly across the BLDC terminals should also work at suppressing the overvoltage. These diodes are designed to absorb an enormous pulse of energy in an overvoltage pulse for a brief period of time, i.e. the switch off instant. You can read more about TVS diodes here.

enter image description here

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  • \$\begingroup\$ Thank you very much, I will attach this solution in my construction. You are talking about TVS diode directly across BLDC driver terminals, but would it be correct to mount it in parallel to MOSFET? It would allow me to do that directly on PCB that is responsible for Low Side switching. \$\endgroup\$
    – Bratw
    Dec 22, 2020 at 16:19

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