LS7635FO
Overview
- 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:
- 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. This eliminates the underlying cause of half-waving.
- Delayed triac turn-on and safety shutdown With inductive loads, the holding current needed to maintain the triac On-State, may seriously lag behind the gate trigger signal causing the triac to turn off prematurely. If the frequency of occurrences of the delayed turn-on exceeds a preset threshold, a shutdown is initiated by turning off the triac trigger pulses. The safety-shutdown threshold value is accumulated in a 4-bit Up/
