Digital LED drivers combine wide dimming range and low BOM
Following the introduction of its single-stage LED driver for non-dimmable incandescent bulb replacement applications earlier this year, iWatt is debuting the iW3606 (8W output power) and iW3608 (15W output power), giving LED bulb manufacturers an alternative approach to significantly lower cost and tackle the lifetime and performance issues in dimmable applications. Both new LED drivers allow solid-state lighting (SSL) designers to reduce their bill of materials (BOM) cost by 20% to 40% compared to competitive solutions. The iW3606 and iW3608 incorporate configurable over-temperature protection (OTP) and derating functionality to provide predictability and reliability of bulb operating life and offer what the company believes is the industry’s lowest pop-on current: The LEDs show response already at less than 5% of light output.
Designed for retrofit bulbs, including candle and GU10 lamp replacements used in existing phase-cut dimmer installations, the iW3606 and iW3608 tackle the key issues that could impact consumer adoption of SSL lighting, including poor dimming performance (pop-on, popcorning, dead travel, drop-out, flicker), short bulb lifetime or failure, as well as high cost. Both drivers meet or exceed global regulations for power quality and efficiency with a high power factor (PF) of > 0.92, low total harmonic distortion (THD) of < 20%, and high efficiency ³ 82%. The iW3606 and iW3608 have already been designed in to the next-generation of dimmable SSL bulb products from key iWatt customers.
The on-chip over-temperature protection (OTP) and derating feature of the iW3606 and iW3608 addresses the thermal issues caused by the high and unpredictable operating temperatures in dimmable SSL applications. The lifetime of many of the components in the LED driver circuit, especially electrolytic capacitors, degrades as temperatures increase, potentially reducing overall bulb lifetime to less than 2,000 hours, well under the 30,000 to 50,000 hours expected for SSL bulbs. iWatt’s OTP derating monitors the temperature inside the sealed SSL bulb and when thermal conditions reach a point set by the system designer, the LED drivers automatically reduce the current drive to the LEDs, lowering the power dissipation and resulting in cooler overall operation. This helps prevent exceeding the temperature rating of the electrolytic capacitors in the system and thus to ensure a predictable and safer bulb operating life.
The iW3606 and iW3608 feature a wide, flicker-free dimming range from 100% down to 1% of measured light, to closely match the dimming performance of incandescent bulbs. This enables the smooth, “natural” dimming consumers expect, with no light drop-out at the low end of the dimming range and virtually no dead travel where the light turns off before the dimmer control reaches the bottom of its travel. The very low internal power consumption of the iW3606 and iW3608 allows them to start at a very low dimming level of < 5% of light output. This virtually eliminates pop-on, a phenomenon where the light does not turn on at low dimmer levels and as the dimmer level is raised, the light suddenly turns on. This also helps eliminate so-called popcorning effects, in which various bulbs in multiple-light installations on the same dimmer circuit can turn on one after the other at different dimmer setting thresholds.
The configurable dimming curves of both parts are compliant with the NEMA SSL 6 dimming standard. Both devices also use a digital dimming technology with embedded intelligence that detects dimmer characteristics to provide wide dimmer compatibility, including leading edge (TRIAC), trailing edge and non-traditional R, R-C and R-L types, with automatic dimmer detection.
The iW3606 and iW3608 enable approximately 40% and 20% lower BOM costs (respectively) compared to competitive single-stage solutions, which can require as many as nine additional external components. The lower BOM costs are achieved via high levels of integration, including on-board OTP and derating, along with replacing field effect transistors (FETs) with lower-cost bipolar junction transistors (BJTs). A combination of BJTs and valley mode switching lowers electromagnetic interference (EMI) and reduces the need for external EMI filtering components. They also eliminate the need for a secondary-side regulator and optical feedback isolator. Additional savings come from the standard, low-cost 8-lead SOIC package, which can be used in single-layer PC boards for additional cost savings and a smaller design footprint.
For more information visit www.iwatt.com
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