# Designing for power that cuts out

Power cuts and voltage dips are common in many places. A device should handle them safely and recover on its own.

Page: https://dharanova.com/learn/unreliable-power · Track: Power · Level: Deep dive · Facts last checked 6 October 2026

Read first: [LDOs, buck converters and PMICs](https://dharanova.com/learn/regulators.md), [Sleep modes and waking up](https://dharanova.com/learn/low-power-modes.md)

Diagram: Top, not to scale: supply voltage dips below the brown-out threshold and recovers; the chip runs, is held in reset while the supply is below the threshold, then runs again. Middle: after the supply fails, the device voltage without hold-up drops at once, while with a hold-up capacitor or supercapacitor it decays slowly for milliseconds to tens of seconds, long enough to finish a write, send a last message or shut down cleanly. Bottom: a cut-off write can leave flash or a filesystem inconsistent; power-cut-tolerant designs use journaling, copy-on-write, or a read-only root filesystem.

## Key points

1. A brown-out detector resets the processor when its supply drops below a safe threshold and holds it in reset until the supply recovers, so the chip does not run unreliably while the voltage sags. [1]
2. A write interrupted by power loss can leave flash or a filesystem inconsistent; power-cut-tolerant designs use journaling or copy-on-write filesystems, or keep the root filesystem read-only. [2][3][4]
3. A hold-up capacitor or supercapacitor can keep a device running for the milliseconds to tens of seconds needed to finish a write, send a last message or shut down cleanly after the supply fails. [5][6]

## Sources

1. [RP2350 datasheet](https://datasheets.raspberrypi.com/rp2350/rp2350-datasheet.pdf), Raspberry Pi
2. [Linux kernel: UBI File System](https://docs.kernel.org/filesystems/ubifs.html), kernel.org
3. [littlefs design](https://github.com/littlefs-project/littlefs/blob/master/DESIGN.md), littlefs project
4. [Preventing Filesystem Corruption in Embedded Linux (updated 17 Dec 2020)](https://www.embeddedts.com/assets/preventing-filesystem-corruption-in-embedded-linux), Technologic Systems (embeddedTS)
5. [TIDA-00304: 'Last Gasp' Hold Up Energy Storage Solution (TIDU506)](https://www.ti.com/lit/ug/tidu506/tidu506.pdf), Texas Instruments
6. [Effective Ways to Implement Backup Power from Supercapacitors (SSZT121)](https://www.ti.com/lit/ta/sszt121/sszt121.pdf), Texas Instruments