LED lighting simplified with direct-AC-drive chips

May 21, 2016 // By Graham Prophet
Fairchild’s FL77944 is the first product in an LED Direct AC Drive family of solid-state LED lighting solutions that manufacturers can use to scale power and create smart and scalable LED-based lighting products that can be smaller, have higher performance and a longer system lifetime compared to products using the switch mode power supply (SMPS) approach.

LED direct AC drive has only had limited use, Fairchild says, because of the issue flicker (at mains frequency). This product, the company says, can reduce the flicker effect and allow the concept to be applied to commercial and industrial lighting. The IC offers good power factor and total harmonic distortion of under 20%; it supports dimming by analogue and pulse width modulation and can scale from 10 to 120W lighting systems, by parallel connection.

Flicker is specified by the peak-to-average ratio of the light emitted. The IC can be operated without energy storage (that smooths the dips in the light level) in which case it delivers a flicker factor of around 0.3; by adding four, 100 µF capacitors, this can be reduced to under 0.15, as demanded by commercial applications.

The FL77944 has, Fairchild says, all the important dimming capabilities required for smart lighting products, including phase-cut dimming as well as analog and PWM dimming, which is also key for wirelessly connected lighting. The FL77944’s ability to scale to support higher power applications up to 120W by wiring products in parallel is a critical feature. This reduces the number of different ICs that manufacturers need to keep in inventory. The FL77944 can eliminate the need for electrolytic capacitorss, transformers and inductance coils. This reduces both the bill-of-materials (BOM) costs and the overall complexity compared to designs using SMPS. It enables designers to reduce their board space requirements by locating the controller IC on the same PCBs as the LEDs and by eliminating the need for many passives.