: Its job is to provide a low-impedance path to ground during system startup and shutdown. This prevents that annoying (and potentially speaker-damaging) "pop" sound when you turn on a portable device.
I provided them with —specifically, the hidden “Switching Node Layout” figure on page 14, which is omitted entirely from the public version. Within one week, they rev2’d the board:
The AC line feeds directly into the load. The return path is actively gated by . The MY9892 monitors line frequency via R1 . As you turn RV1 , the voltage at the CTRL pin shifts, altering when the gate drive fires during each half-cycle.
Given the proprietary nature of this document, it is not available on Ultra Librarian, Octopart, or any of the usual aggregators. The manufacturer does not host it publicly because it contains engineering notes that could be considered "too transparent" for their less sophisticated customers.
: Smooth control for fans, pumps, and power tools like grinders.
: Ceiling fans, water pumps, and compressor motors. These depend on frequency (Hz) rather than voltage. Attempting to use this module will cause buzzing, overheating, and motor failure.