Bill,
The round component in the center of the second drawing is an SBS [Silicon Bidirectional Switch]
This switch can control / pass AC, like the Triac does, except the Triac is a better amplifier for this type of job.
The SBS can be thought to be "madeup" of two SUS [Silicon Unidirectional Switch], in order to pass currents in both directions.
Similar to the way a Triac can be thought of as "madeup" of two SCR [Silicon Controlled Rectifier], in order to pass currents in both directions.
Scott SET
