[SP] should probably have snubber diodes near the fans

oxidecomputer / gemini-bringup

EDA work for the Gemini bringup vehicle

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[SP] should probably have snubber diodes near the fans #31

Closed cbiffle closed 4 years ago

cbiffle commented 4 years ago

The fans are inductive loads, and while most computer fans I've disassembled contain their own clamping diodes, I don't know that I trust it. So, it would be polite to put diodes near the fan connectors. Our 12V system can actually tolerate up to 36V input, so ~15V Zeners should do the job without accidentally activating in response to a crappy 12V supply or an automotive-style 13.6V supply.

cbiffle commented 4 years ago

@kc8apf notes that, since our 12V-3V supply tolerates up to 36V, we probably don't actually care if a cheap fan dumps some back EMF onto the 12V rail -- as long as it's relative to 12V and not (say) 48V. As long as any potential 48V adaptor has appropriate diodes, I don't think we need them on the base board.