New driver IC architecture seeks to reduce bill of materials cost in 8–15W retrofit lamps while still supporting smooth dimming over a 1–100% range.
iWatt has introduced the iW3202/08 LED driver ICs that primarily target retrofit lamps ranging from candle bulbs to A19 omni-directional lamps to LED T8 tubes. The new IC leverages a single-stage topology that minimizes the bill of materials (BOM) cost while still supporting power factor correction, smooth dimming, and over-temperature protection (OTP).
Scott Brown, iWatt vice president of marketing, said that the 8W iW3606 and 15W iW3608 deliver a 40% and 20% BOM reduction, respectively, relative to competitive driver ICs. The savings come through integrated features such as the OTP functionality and the fact that solid-state lighting (SSL) designs can use lower-cost bipolar junction transistors (BJTs) in place of MOSFETs.
The OTP feature is based on an on-chip sensor that monitors the actual die temperature of the IC. Product developers can set the temperature at which the driver begins to reduce output current to the LEDs when an over-temperature condition exists. Through a resistor, the set point can be 100°C, 105°C, 110°C, or 115°C. Brown said that in most cases a person would not even notice the slight reduction in light output when the OTP function is active.
Brown explained that the impact of the OTP feature on lamp cost plays out in more ways than one. Obviously, an SSL manufacturer would have to implement OTP functionality in additional external components were it not in the chip, or risk a less reliable lamp design. But the current derating capability can be used to manage temperature and that could allow the use of less expensive electrolytic capacitors while still ensuring long lamp life.
iWatt used its experience in dimmable two-stage drivers, based on a digital dimmer detection circuit, to also implement full-range dimming in the new ICs. Brown said the lamps would not pop on, and also said the IC ensures that lamp customers don't experience popcorning when multiple lamps are connected to the same dimmer. Popcorning refers to lamps coming on at different times as a users adjust a triac dimmer.
"The challenge with dimmable SSL bulbs is in delivering a similar lighting experience to that of incandescent dimmable bulbs at low cost with long lifetime," said Zhang Wenlong, general manager at Xiamen Tenia Lighting & Electrical Co. Ltd. "We selected the iW3608 because of its excellent compatibility with dimmers and the configurable OTP derating allows us to deliver the bulb lifetime and safety consumers expect, all with a low BOM cost and reduced potential for warranty issues."
The new driver ICs can deliver a power factor in excess of 0.92 with total harmonic distortion below 20%. Moreover, the electrical efficiency is greater than 82%. About the Author Maury Wright is the Editor of LEDs Magazine.
