Single-phase rectifiers are commonly used for power supplies for domestic equipment.

The direct current produced by a single-phase rectifier thus contained a varying component (ripple) at twice the power supply frequency, which was undesirable in many applications for DC.

Although better than single-phase rectifiers or three-phase half-wave rectifiers, six-pulse rectifier circuits still produce considerable harmonic distortion on both the AC and DC connections.

This excitation or keep-alive circuit was absolutely necessary for single-phase rectifiers such as the excitron and for mercury-arc rectifiers used in the high-voltage supply of radiotelegraphy transmitters, as current flow was regularly interrupted every time the Morse key was released.