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I've heard that the Vrrm of a diode is a maximum, and the diode should not be continuously exposed to it. I'm using a PMEG4010CEJ diode, a 40V/1A SOD323 diode. Basically, the power input is a 33.6V 8S LiPo battery, which could be reversed. The diode is in series with the power input and protects a buck converter against a reversed supply, which would damage it. To add a bit of a margin, let's say the system has to sustain a maximum -40V input fault. Can this diode (or any 40V diode) handle it, or do I need to use a 50-60V diode (more expensive)?

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Exceeding the PIV will generally damage the diode, not to mention rapidly allowing current to flow - defeating the point of the protection diode.

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Derating guidelines in industry usually allow for no more than 70-80% of the maximum reverse voltage stress for diodes. You'll want a 50V part for 33.6V reverse protection.

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  • \$\begingroup\$ Side question: I'm using an LT1933. In the datasheet, for 34V in and 3.3V out, they recommend a 40V catch diode. If I'm not mistaken, isn't the catch diode exposed to full brunt of the supply's 34V about 550,000 times per second? \$\endgroup\$
    – Thomas O
    Feb 18, 2011 at 12:30

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