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I would like to know how fast a typical body diode of a modern MOSFET is in terms of letting a voltage spike through. In the datasheets, only the reverse recovery is stated for blocking again, but nothing about how fast a forward transient can be. Are we here in the range of under 1ns and is this normally neglectable?

Edit: If we for example have a look at the following MOSFET (FDMS3D5N08LC): https://www.onsemi.com/pdf/datasheet/fdms3d5n08lc-d.pdf

There is nothing specified about how fast this diode turns on, but there is a voltage limit of 1.2V specified. So can this take several ns to several 10 of nanoseconds to turn on and so fast voltage spikes cannot be prevented by the body diode itself?

Further I made a LTSpice simulation and there is seems with a real MOSFETs body diode, the turn on time is way under 1ns. The thing is, I think the most delay comes from the parasitic inductances, when we take them into account, there is way more delay:

Without parasitic inductance: enter image description here

With parasitic inductance: enter image description here

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    \$\begingroup\$ Slow ............ \$\endgroup\$
    – Russell McMahon
    Oct 23, 2021 at 10:09
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    \$\begingroup\$ the rising spike can always travel through the capacitances, so it doesn't matter. \$\endgroup\$
    – tobalt
    Oct 23, 2021 at 10:15
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    \$\begingroup\$ I would not rely on the body diode unless everything you need is specified (and thus guaranteed). When using a MOSFET without that data, I would simply put a fast (Schottky) diode in parallel with the body diode and rely on that diode. \$\endgroup\$ Oct 23, 2021 at 11:55

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The timing performance of that diode, if important, is stated in the datasheet.

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