Hold-Up Time and Ride-Through: Surviving a Brown-Out

The mains is not perfect — it dips, sags and drops out for brief moments. Hold-up time is how long a power supply can keep its output up after the input disappears, and it is what stops a momentary glitch from rebooting your equipment.

Where it comes from

The energy is stored in the supply’s bulk input capacitors. When the mains drops, the supply runs off that stored charge. Typical hold-up is 10–20 ms at full load — enough to ride through a missing mains cycle (one cycle is 20 ms at 50 Hz).

Why load matters

Hold-up is quoted at full load. Run the supply lightly loaded and it holds up much longer, because the stored energy drains more slowly. If ride-through is critical, do not load the supply to its limit.

Extending it

• Oversize the supply so your load is a smaller fraction of its rating.
• Add a DC UPS or buffer module for hundreds of milliseconds or more.
• For a true outage, a battery-backed UPS takes over where hold-up ends.

Browse the UPS range or tell us your ride-through target and we will size it.