New Industry Products

iWatt High PFC Digital LED Driver IC Delivers Flicker-Free Dimming for Commercial & Industrial Lighting

February 08, 2011 by Jeff Shepard

iWatt, Inc. expanded its family of digital LED driver ICs with a two-stage, power-factor-corrected (PFC), primary-side-regulated, leading- and trailing-edge-dimmable, ac-dc Digital PWM Controller targeting 120/230Vac offline commercial and industrial LED lighting applications.

Designed for isolated or non-isolated LED drivers used in incandescent replacement lamps including both space-constrained (GU10, MR16) and larger (A, PAR) types, the iW3614 (3 to 15W) incorporates features to assure power efficiency, durability, reduced size and component costs, and flicker-free compatibility with existing wall dimmers worldwide.

The iW3614 joins its siblings, the medium-power iW3610/iW3612 ICs and low-power iW3602, as iWatt’s first LED driver IC targeted for commercial and industrial LED lighting applications with PF > 0.9. All four ICs are pin compatible, and the iW3602/iW3612/iW3614 include hot-plug support, where the user can swap the LED engine without recycling the input power for the LED driver.

The iW3614 features a two-stage PFC scheme on a single chip. A front-stage boost converter enables PF > 0.90 (typically 0.94), while the following PWM driver stage minimizes ripple current at the output. This scheme eliminates the disadvantages of a single-stage design, such as the low 100Hz/120Hz line frequency ripple and resulting flicker at the output. Reducing the output ripple current also enables smaller output capacitors, leading to size, cost and reliability benefits.

The low-frequency (100Hz/120Hz) flicker common to single-stage PFC solutions has the potential to cause headaches, migraines, eye strain and other ill effects, and is currently under scrutiny by the IEEE standards working group, the IEEE PAR1789. "The power savings that make LED lighting solutions attractive will be undermined if they cause significant health risks to the public," said Ron Edgerton, CEO of iWatt. "Our engineers are looking at ways to preserve the industry’s energy-efficiency benefits and avoid the potential health risks."

A single-stage PFC design can also limit the dimming range (typically 10% to 100%) as it may lack a bulk electrolytic storage capacitor to store energy and subsequently power the LEDs when the dimmer phase cut is low. iWatt’s two-stage design overcomes this challenge with a small bulk storage capacitor to allow a wide (1% to 100%) dimming range.

In iWatt’s LED driver ICs, intelligent digital algorithms automatically detect all types of dimmers or a lack thereof, for flicker-free operation with existing wall dimmers worldwide, including both leading-edge (TRIAC style) and trailing-edge dimmers. In case of an unsupported dimmer, safe mode shuts it down. The device allows smooth, flicker-free dimming with tight ±5% LED current regulation which prevents flicker from the noisy line voltage common on a factory floor.

iWatt’s ac-dc power conversion ICs are unique in that they feature a digital feedback and control loop versus analog. This adaptive digital control technology optimizes efficiency and reliability, and simplifies printed circuit board (PCB) design. Precision primary-side-control technology to eliminate the opto-coupler and secondary-side control circuit, built-in frequency jitter and quasi-resonant (or valley-mode) switching to reduce EMI (over 6dB margin and over 85% efficiency), and a high switching frequency up to 200kHz combine to enable designers to reduce thermal loss, component count, driver size and bill of materials (BOM). Eliminating the opto-coupler, combined with low inrush current and low ripple current by design, can also lengthen the life of the LED driver assembly.

Comprehensive safety features include: LED open/short circuit protection, input over-voltage protection, and over-temperature thermal shutdown. An LED current de-rating at high temperatures also protects LEDs. The IC enables system designers to exceed all safety, EMI and regulatory standards, including the EN55015B, IEC61000-3-2 and Energy Star.

The chip comes in a low-cost, thermally-enhanced SO-8 package with an exposed pad which allows lower die junction-to-PCB thermal resistance for increased reliability. Samples are available, and the iW3614 is priced at $1.13 in 1,000-piece quantities.