Why power loss can corrupt SD card?

[mgrouch]

Here is some good explanation:

From Reddit

https://www.reddit.com/r/embedded/comments/1b7v1zy/why_do_sd_cards_get_bricked_due_to_the_power_loss/

Quote:

It's generally not power loss that corrupts SD cards, it's the small amount of time where they're under-volted as the supply drains down. If a write is taking place - especially to the FAT, and the voltage begins to fall, the write kind of completes, but there isn't enough voltage to really set the bits properly. Boom, corrupted FAT.

The SD card is also not likely to be truly bricked - just corrupted. Formatting the card will bring it back to life in most cases.

Often, a diode in series with the SD card power and a moderately sized capacitor is enough to allow the SD card to finish writing the last transaction before the power fails entirely. There are also SD Cards available that have this power hold up circuit embedded in them so as to be power fail safe. These are often marketed as "Industrial" or "High Reliability" products.