Author:
Reported by Cliff Keys, Editorial Director, PSD
Date
02/24/2012
PDF
I had the pleasure to talk with Brian Johnson, Fairchild's lighting specialist, about the company's Single-Stage PFC Primary Side Regulation LED Driver which minimizes bill-of-materials, allows for more compact, longer life, lower system cost design. LED lighting has evolved into a promising solution for replacing conventional lighting sources, such as fluorescent and incandescent lights. However, designers face several obstacles in residential and commercial LED lighting applications up to 20W including bulb, down lighting (GU10/E17, E26/27, PAR30/38) and Tube/Bar. Implementing dimming capabilities in a conventional TRIAC dimmer infrastructure is challenging because of dimmer compatibility. Additionally, small space requirements remain a consideration.
This highly integrated PWM controller, FL7730MY, provides several features to enhance the performance of single-stage flyback converters. The proprietary topology, TRUECURRENT™, enables the simplified circuit design for LED lighting applications. TRIAC dimming is smoothly managed by dimming brightness control without flicker. By using single-stage topology with primary-side regulation, an LED lighting board can be implemented with few external components and minimized cost. It does not require an input bulk capacitor or feedback circuitry. To implement good power factor and low total harmonic distortion, constant on-time control is utilized with an external capacitor connected to the COMI pin. Precise constant-current control regulates accurate output current versus changes in input voltage and output voltage. The operating frequency is proportionally changed by the output voltage to guarantee Discontinuous Conduction Mode (DCM) operation with higher efficiency and simpler design. The FL7730MY provides protections such as open-LED, short-LED, and over-temperature protections. Current-limit level is automatically reduced to minimize output current and protect external components in a short-LED condition.
The FL7730MY frequency-hopping function in the oscillator improves EMI performance. The FL7730MY controller is available in an 8-pin SOP package. To help designers address these challenges, Fairchild Semiconductor (NYSE:FCS) developed the FL7730 single-stage primary side regulation (PSR) controller with power factor correction (PFC), TRIAC and analog dimming compatibility, as well as the FL7732 for non-dimming applications. This highly integrated PWM controller provides several features to enhance the performance of low-power flyback converters. The proprietary topology enables simplified circuit design for LED lighting applications. By using single-stage topology with primary-side regulation, a LED lighting board can be implemented with few external components and minimized cost. No input bulk capacitor or feedback circuitry is required. To implement good power factor and low THD, constant on-time control is utilized with an external capacitor connected to the COMI pin. Precise constant-current control regulates accurate output current versus changes in input voltage and output voltage. The operating frequency is proportionally adjusted by the output voltage to guarantee DCM operation with higher efficiency and simpler design.
FL7732 also has a frequency-hopping function in the oscillator for better EMI performance. The FL7732 controller is available in an 8-pin SOP package. The FL7730 is an active PFC controller for single-stage flyback topology application. The device supports both TRIAC and analog dimming. Implemented with Fairchild's unique analog sensing technology, the device can achieve TRIAC dimming control without flicker over the full range of 0 to 100% light output. The FL7730 and FL7732 combine primary-side regulation and a single-stage PFC topology to minimize total bill-of-material (BOM) count, such as an input electrolytic capacitor and feedback circuitry, therefore allowing for a more compact, longer life, and lower system cost design. To improve power factor and THD, both devices feature constant on-time control with an internal error amplifier and low bandwidth compensator. Precise Constant Current accuracy/control (± 5 percent) regulates accurate output current, independent of input and output voltage, allowing designers to achieve high and improved lighting quality. Operating frequency is proportionally adjusted by output voltage in both devices to guarantee DCM operation with optimized PF/THD and simpler design. Excellent PF (?0.9), low total harmonic distortion (THD) (Class C) and power efficiency of up to 85 percent for the FL7730 - greater than 85 percent for the FL7732 in non-dimming applications - allows these devices to meet worldwide energy saving regulations. Fairchild offers a total solution portfolio for low- (<20W), mid- (20W to 50W) and high- (>50W) LED driver applications. Our highly integrated PWM and PFC controller solutions reduce component BOM counts to enable smaller lamp sizes and eliminate design complexities, while improving overall lighting efficiency. Fairchild's extensive product portfolio ranges from discrete devices to integrated solutions that contain PFC controllers, high voltage gate drivers and MOSFETs. With a commitment to energy savings and meeting the most stringent regulations, Fairchild has developed innovative products that maximize performance while reducing board space, design complexity and system costs. In addition, Fairchild's Global Power ResourceSM Center comprised of online tools, FAEs and regional centers staffed by power engineers, is the industry standard for customer design support. Price: US $ in 1,000 quantity pieces FL7730: $1.27 FL7732: $1.15 Availability: Samples available upon request. Delivery: 8-12 weeks ARO www.fairchildsemi.com
