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LED driver offers mood-enhancing ambiance to SSL bulbs

01 Apr 2014

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Dialog Semiconductor introduced its iW3640 solid state lighting (SSL) LED driver, designed to bring mood-enhancing ambiance to price-sensitive SSL bulbs. The iW3640 2-channel, 25W SSL LED driver offers a dimmable colour-mixing solution to achieve warm incandescent-like dimming while eliminating the need for a microcontroller and dedicated power supply. This reduces the bill of materials (BOM) cost for 75W to 150W-equivalent A19 SSL and PAR bulbs, as well as 20W to 45W commercial dimmable external lighting ballasts.

While typical LED bulbs retain the same harsh white colour as they dim, the dual driver output of the iW3640 lets designers use amber LEDs in parallel with the main white LEDs allowing LED bulbs to gain warmth as they dim. Dialog's patented, built-in digital dimming technology detects the dimmer type and phase—automatically adjusting LED colour mixing in step with light intensity to provide smooth dimming that closely matches the warmth and ambiance of a traditional dimmable incandescent bulb. The result is a much more intimate LED lighting experience in residential and commercial settings, where lighting plays an important role in setting the mood.

By integrating the driver for a second string of LEDs and using the digital engine to control transitions, the iW3640 eliminates the cost of the external MCU and dedicated power supply required by conventional warm dimming techniques.

Dialog's digital dimming technology allows the iW3640 to work with virtually all phase-cut wall dimmers, including leading-edge dimmers (R-type or R-L type) and trailing-edge dimmers (R-C type), as well as digital dimmers. The iW3640 adjusts light temperature from bright white down to warm amber, with flicker-free dimming down to 1 per cent of initial brightness. As the driver detects increased dimming angles, the duty cycle of the secondary LED string is also increased, creating more warmth as the design goes deeper into dimming. Additionally, cycle-by-cycle waveform analysis technology facilitates fast dimmer setting response.

The iW3640 addresses bulb overheating issues by including an over-temperature protection (OTP) derating function that monitors the temperature inside the sealed SSL bulb. The OTP feature is configured via an NTC resistor, and when thermal conditions in the bulb reach the temperature pre-set by the designer, the iW3640 automatically reduces the current drive to the LEDs in small, imperceptible increments, then seamlessly restores brightness as temperature falls, with no need for a full shutdown.

This allows the electrolytic capacitors in the LED circuit to operate within the maximum lifetime of the SSL bulb, resulting in a predictable bulb operating life, and helping to ensure the long-term reliability and safety consumers expect from LED replacement bulbs. Additional iW3640 safety features include LED open/short circuit, over-current, current sense resistor short-circuit, and input over-voltage protection.

The iW3640 two-stage AC/DC SSL LED driver meets global regulations for power quality and efficiency, including the European Union IEC61000-3-2 standard, with a high power factor of >0.95, low total harmonic distortion <15 per cent, and low ripple voltage <20 per cent. It is compatible with the Zhaga hot-plug LED module for LED light interchangeability and the configurable dimming curves are compliant with the NEMA SSL 6 dimming standard.

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