What causes the high-frequency, ascending-pitch sound coming from a camera's flash unit when charging.
Asked by: Robert Smith
The electronic flash uses a solid state oscillator to step up a low voltage to a much
higher one. The oscillator uses a transistor(s) to chop the low voltage DC into pulsating DC
which can be stepped up by a transformer, the output of the transformer is then rectified
(converted to DC) and used to charge a capacitor. The whistling you hear is mostly due to the
transformer vibrating at the oscillator frequency although some capacitors are also capable
of making some sound. The pitch rises after each flash because the oscillator isn't very
well regulated and the discharged capacitor presents a heavy load to the oscillator, as the
capacitor charges the load decreases and the frequency rises.
Answered by: James Hess, President, Hess Electric, Inc.