Output retention time

Even if the input voltage is turned off in a power supply circuit, the output voltage does not immediately drop to zero but gradually decreases to zero over a certain period of time. At this time, the duration during which the output voltage remains within the specified range of the rated voltage corresponds to the hold-up time. The longer the hold-up time, the less susceptible the circuit is to the effects of momentary input voltage drops (instantaneous power interruptions) in the input voltage.