I was reading this thread and decided that in general it's better to place the reverse polarity protection diode D2 after the TVS rather than before it, and to instead use a bidirectional TVS for D1 (note that it is unidirectional in the image):

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In this configuration, the TVS will prevent reverse polarity through itself under normal operating conditions and not cause the fuse to blow. Further, in the event of a negative surge, the reverse polarity protection diode will not be in the surge path and have less risk of damage.

Is there any drawback to this configuration in terms of protection?


1 Answer 1


Looks fine to me.

While the 2961 is rated for high transient voltages, there is no need to stress it unnecessarily. I would reduce the value of the TVS to something lower than 26 V.

Note that polyswitch fuse characteristics change with each overcurrent cycle.

  • \$\begingroup\$ In my design I'll be using a switcher instead, but in general I wanted to know if there's any drawback to putting the Schottky in front of the TVS. I can't seem to find much documentation on the positioning of these components. \$\endgroup\$
    – Alenux
    Jan 15, 2019 at 1:18
  • \$\begingroup\$ The drawback would be what you said, routing transient currents through it. It would reduce the reverse polarity current to zero (so you could use a unipolar TVS), but I like it after the TVS. \$\endgroup\$
    – AnalogKid
    Jan 15, 2019 at 1:41

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