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LNK458V Datasheet(PDF) 4 Page - Power Integrations, Inc. |
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LNK458V Datasheet(HTML) 4 Page - Power Integrations, Inc. |
4 / 12 page Rev. A 06/10 4 LNK454/456-458/460 www.powerint.com This document contains information on a new product. Specifications and information herein are subject to change without notice. PRELIMINARY TRIAC (Phase-Controlled) Dimming The LinkSwitch-PL integrates several features to improve dimming range and reduce external circuit complexity when using a phase-controlled TRIAC dimmer. The output LED current is controlled by the FEEDBACK pin voltage which changes proportionally to the TRIAC dimmer conduction angle. The conduction angle decreases, the voltage at the FEEDBACK pin decreases causing the average LED current to decrease. The FEEDBACK pin voltage adjustment is initiated at approxi- mately 20% of the main half-cycle duration. When this (jOS) threshold is exceeded, V FB and the output LED current are reduced until a second phase angle threshold is reached. When this happens, with the TRIAC conduction angle being very limited, the IC runs open loop (jOL region) and the integrated MOSFET processes as much power as the heavily chopped input voltage will allow creating a light output that is deeply dimmed. The 520 mV clamping feedback threshold is also linearly reduced during dimming to control LED current ripple. To help maintain the holding current of the TRIAC in the dimmer, LinkSwitch-PL extends the MOSFET on-time towards the zero crossings of the AC input voltage providing an active bleed or holding current function. This on-time extension is carefully limited to avoid deterioration of input current harmonic content and limit total harmonic distortion (THD). Figure 6. Feedback Voltage vs. Phase Angle Dimming Characteristics. VFB(ϕ) VFB(ϕ) VFB ϕOL ϕ ϕ 180° 0° VLINE Phase Angle Phase Angle TRIAC Conduction TRIAC Conduction Leading Edge TRIAC Dimmers Trailing Edge TRIAC Dimmers VTRIAC 180° 0° 0° 0° PI-5894a-052610 ϕOS ϕOL ϕOS Phase Angle Phase Angle Phase Angle Phase Angle |
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