ECN Forum Forums Technical Discussion Electrical Theory and Applications What's inside a Dimmer?

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

Bill:

Don't let all the different terminology get too confusing. The SBS name Scott used is what I referred to as a diac. Just a different name.

An SCR (Silicon Controlled Rectifier) is also called a thyristor, a solid-state equivalent to the old thyratron vacuum tubes.