Products, Materials & Tools | Apr 06, 2012

Allegro MicroSystems, Inc. Introduces New Single Stage Off-Line LED Driver IC Series

Allegro MicroSystems, Inc. introduces the LC5540LD/LF single stage power factor corrected off-line LED driver IC series which is manufactured and developed by Sanken Electric Co., Ltd. in Japan. The robust functions within these single stage converters have been developed to simplify system designs. This new series is targeted at the consumer and industrial markets targeting indoor and outdoor LED lighting and off-line LED lighting applications.

Main Features and Benefits:
• Integrated on-width control circuit (it realizes high power factor by average current control)
• Integrated startup circuit (no external startup circuit necessary)
• Integrated soft-start circuit (reduces power stress during start-up on the incorporated power MOSFET and rectifier)
• Integrated bias assist circuit (improves the startup performance, suppresses VCC voltage droop during operation, allows reduction of VCC capacitor value as well
as use of a ceramic capacitor)
• Integrated Leading Edge Blanking (LEB) circuit
• Integrated maximum on-time limit circuit
• Dual-chip structure, with an avalanche-guaranteed power MOSFET (allows simplified surge suppressing circuits)

Protection features:
▫ Overcurrent protection (OCP): pulse-by-pulse
▫ Overvoltage protection (OVP): latched shutdown
▫ Overload protection (OLP): latched shutdown
▫ Thermal shutdown (TSD): latched shutdown

The LC5540LD/LF series are quasi-resonant topology switching power supply ICs, designed for input capacitorless applications making it possible for systems to comply with the harmonics standard (IEC61000-3-2 class C). These devices incorporate separate controller and power MOSFET chips. The controller adapts the average current control method for realizing high power factors, and the quasi-resonant topology contributes to the high efficiency and low EMI noise. The rich set of protection features helps to realize low component counts and high performance-to-cost power supply.

These devices are intended for isolated designs. The incorporated MOSFET has a VDSS(min) rating from 650 V (LC5545LD, LC5546LD, LC5546LF, and LC5547LF,) to 800 V (LC5548LD and LC5549LF). The RDS(on)(max) is 1.1 Ω (LC5547LF), 1.9 Ω (LC5546LD and LC5546LF,) and 3.95 Ω (LC5545LD). These devices are capable of a maximum output power of 20 to 80 W on a 230 VAC supply to 16 W (LC5546LD) to 55 W (LC5547LF) on a universal supply based on the thermal rating. Note that the maximum output power can be up to 120% to 140% of this value. However, it may be limited in applications with low output voltage or short duty cycle.

This series is available in the DIP8 and TO220 packages that have been designed to protect the IC and overall system from excessive heat. Similar competitive designs on the market cannot easily detect the power MOSFET rising temperatures.

About Allegro MicroSystems:

Allegro MicroSystems, Inc. is a leader in developing, manufacturing and marketing high-performance semiconductors. Allegro's innovative solutions serve high-growth applications within the automotive market, with additional focus on office automation, industrial, and consumer/communications solutions. Allegro is headquartered in Worcester, Massachusetts (USA) with design, applications, and sales support centers located worldwide. Further information about Allegro can be found at


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