Part # Application Notes Power Supply And Power Management L6562A TSM1052 AN2711 datasheet

Part Manufacturer: ST Microelectronics

ST Microelectronics

Part Description: 15 W offline TRIAC dimmable LED driver


Part Details:

AN2711 Application note 15 W offline TRIAC dimmable LED driver Introduction The cost of power LEDs is rapidly coming down, while performance is improving. Their efficacy (light out per watt in) is now competitive with compact fluorescent lamps, while their life is significantly longer at 100,000 full-power hours (11+ years) to half brightness. Dimming of LEDs can extend the lifetime further and also reduces power drain. By far the most common dimming method is the TRIAC phase-control dimmer, which replaces the AC on-off switch directly, but can be used only on incandescent lamps and specially designed fluorescent ballasts. This application note presents a low-cost driver for LEDs that is compatible with TRIAC phase-control dimmers. The design gives luminaire manufacturers a low-cost, commonly available dimming option for home fixtures. A side benefit is that, when not wired to a dimmer, the unit s power factor is over 0.9. The design is based on the L6562A transition-mode PFC controller driving a single stage PFC-flyback power converter. An STMicroelectronics Patent Application is pending for the method for dimming an offline LED driver by means of a TRIAC based dimmer as described in this document. Figure 1. 15 W offline TRIAC dimmable block diagram (STEVAL-ILL016V1) Figure 2. 15 W evaluation board top side Figure 3. 15 W evaluation board bottom side March 2008 Rev 1 1/31 www.st.com Contents AN2711 Contents 1 Main characteristics and brief circuit description . . . . . . . . . . . . . . . . . 5 2 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.1 LED characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.1.1 Heat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.1.2 Speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.1.3 Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.1.4 Color shift with current reduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.1.5 Effects on flicker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.2 TRIAC based dimmers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3 Circut description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 3.1 Deviations from normal PFC-flyback design . . . . . . . . . . . . . . . . . . . . . . . 9 3.2 Electrolytic capacitors eliminated . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 3.3 Damper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 3.4 Housekeeping power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3.5 LED current and voltage regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 4 Test results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 4.1


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