Two-Stage Power-Factor-Corrected Digital LED Driver IC

iWatt Inc. expanded its family of digital LED driver ICs with a two-stage,power-factor-corrected (PFC), primary-side-regulated, leading- andtrailing-edge-dimmable, ac/dc Digital PWM Controller targeting 120V/230V acoffline commercial and industrial LED lighting applications. Designed forisolated or non-isolated LED drivers used in incandescent replacement lampsincluding both space-constrained (GU10, MR16) and larger (A, PAR) types, theiW3614 (3W to 15W) incorporates features to assure power efficiency, durability,reduced size and component costs and flicker-free compatibility with existingwall dimmers worldwide.

The iW3614 joins its siblings, the medium-power iW3610/iW3612 ICs and low-poweriW3602, as iWatt's first LED driver IC targeted for commercial and industrialLED 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 swapthe LED engine without recycling the input power for the LED driver. The iW3614features a two-stage PFC scheme on a single chip. A front-stage boost converterenables PF > 0.90 (typically 0.94), while the following PWM driver stageminimizes ripple current at the output. This scheme eliminates thedisadvantages of a single-stage design, such as the low 100/120Hz linefrequency ripple and resulting flicker at the output. Reducing the outputripple current also enables smaller output capacitors, leading to size, costand reliability benefits.

The low-frequency (100/120Hz) flicker common tosingle-stage PFC solutions has the potential to cause headaches, migraines, eyestrain and other ill effects, and is currently under scrutiny by the IEEEstandards working group, the IEEE PAR1789. A single-stage PFC design can alsolimit the dimming range (typically 10 to 100 percent) as it may lack a bulkelectrolytic storage capacitor to store energy and subsequently power the LEDswhen the dimmer phase cut is low. iWatt's two-stage design overcomes thischallenge with a small bulk storage capacitor to allow a 1 to 100 percentdimming range.

In iWatt's LED driver ICs, intelligent digitalalgorithms automatically detect all types of dimmers or a lack thereof, forflicker-free operation with existing wall dimmers worldwide, including bothleading-edge (TRIAC style) and trailing-edge dimmers. In case of an unsupporteddimmer, safe mode shuts it down. The device allows smooth, flicker-free dimmingwith tight A plus or minus 5 percent LED current regulation which prevents flicker from thenoisy line voltage common on a factory floor.

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

Comprehensive safety features include: LEDopen/short circuit protection, input over-voltage protection andover-temperature thermal shutdown. An LED current de-rating at hightemperatures also protects LEDs. The IC enables system designers to exceed allsafety, EMI and regulatory standards, including the EN55015B, IEC61000-3-2 andEnergy Star. The chip comes in a low-cost, thermally-enhanced SO-8 package withan exposed pad which allows lower die junction-to-PCB thermal resistance forincreased reliability. Samples are available, and the iW3614 is priced at $1.13in 1,000-piece quantities.

Two-Stage Power-Factor-Corrected Digital LED Driver IC