A device that produces an alternating current by periodically interrupting or reversing a continuous steady current from a direct-current source. The vibrator consists of an electromagnetic relay with a vibrating armature that alternately makes and breaks one or more pairs of contacts.

The most common application is in a power-supply unit in which a high-voltage direct current must be produced from a low-voltage d.c. source, such as a battery. The vibrator produces a low-voltage periodically varying current that is transformed (see transformer) into a high-voltage a.c. supply and then rectified to produce a high-voltage d.c. supply. A rectifier circuit may be used to produce the direct-current output or the vibrator itself can be used for this purpose. In the latter case the vibrator (termed a synchronous vibrator) is fitted with an extra pair of contacts that are used to reverse the connections to the secondary winding of the transformer in synchronism with the reversal of the current in the primary winding so that the output from the transformer secondary circuit is a direct current.