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The question: With a dual diode such as the MMBD3004S (datasheet here), are the ratings such as reverse breakdown voltage specified for each diode individually, or for both the diodes combined? There don't appear to be any notes in the datasheet specifying either way although, at a guess, I'd lean towards the former. Hopefully, someone can clarify one way or the other for me.

The context: I'm designing a high-voltage flyback power supply using the LT3420, VOUT of 190V, VBAT of 5V and N of 16. As a result, the peak reverse voltage for the rectifying diode is approximately 450V by my calculation (using the equation on page 12 of the datasheet here).

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The reverse breakdown is for each diode. Two in series will yield double the breakdown voltage.

The LTC datasheet specifies the Vishay GSD2004S SOT-23 type with the diodes in series. That diode has a breakdown of 240V (480V combined), so the Diodes Inc device should be even better, yielding a combined breakdown of 600V.

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    \$\begingroup\$ Two in series doubles the breakdown voltage only if the reverse currents are very well matched. It's likely they will be in a dual package, but it might not be guaranteed. \$\endgroup\$
    – The Photon
    Commented May 1, 2020 at 1:30
  • \$\begingroup\$ Nice one, thank you for the clarification and insight from you both \$\endgroup\$
    – Adzi B
    Commented May 1, 2020 at 1:40

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