LS7634FO

LSI/CSI LS7634 LS7635 LS7634FO LS7635FO U® L LSI Computer Systems, Inc. 1235 Walt Whitman Road, Melville, NY 11747 (631) 271-0400 FAX (631) 271-0405 A3800 October 2008 TOUCH CONTROL HALOGEN LAMP DIMMER FEATURES: Touch or pushbutton control of high-voltage lamps and *transformer-coupled low-voltage halogen lamps *Magnetic Transformers and most Electronic Transformers Automatic Safety Shutdown Three operating modes Extension input for remote activation 50Hz/60Hz AC line frequency +5V Power Supply (VDD -VSS) LS7634, LS7635 (DIP); LS7634-S, LS7635-S (SOIC); LS7634FO, LS7635FO (DIP); LS7634FO-S, LS7635FO-S (SOIC) - See Figure 1 APPLICATIONS: Electronic dimmers for wall switch control of ceiling mounted lighting, foot switch control of large floor lamps and hand switch control of table lamps. BACKGROUND AND GENERAL DESCRIPTION: A typical electronic dimmer may not operate properly with the inductive load encountered when driving a transformer-coupled low-voltage halogen lamp. The inductive load can cause a phenomenon called half-waving, wherein the triac fires in alternate half-cycles only, which may lead to the thermal destruction of the load transformer. The problems encountered in driving an inductive load are addressed by the LS7634/LS7635 family of CMOS ICs as follows: 1. Delayed triac cut-off. When a trigger pulse is due to occur at a conduction angle which coincides with the on-state of the triac, the trigger pulse is delayed until the triac has turned off....