Constant-current LED drivers suitable for edge lighting
As a result of growing demand for smaller LED lighting installations that also provide high efficiency and ultra-low EMI, Diodes Incorporated has extended its BCR420U and BCR421U families of linear LED drivers to include the BCR420UFD and BCR421UFD devices in the ultra-low profile DFN2020 package, making them suitable for 12 and 24V LED edge-lighting applications.
The primary benefits of LED lighting, namely longer lifetime and higher efficiencies, means there is growing demand for more varied and less intrusive solutions. This includes fittings that emit light from the edges as opposed to vertically. In order to meet this demand, manufacturers are looking for solutions that support a thinner overall profile. At 0.6mm in height, the DFN2020 package is suited to edge lighting.
Like other members of the BCR4xxU series, the new devices can deliver an adjustable constant current between 10 and 200mA (BCR420UFD) or 350mA (BCR421UFD) with ±10% tolerance, which in the case of the BCR421UFD can be controlled using a PWM signal of up to 25kHz and a duty cycle of one percent to provide LED dimming functionality.
Both devices include a negative temperature coefficient, which lowers the LED driver current as the internal temperature rises, thereby protecting and extending the lifetime of the LEDs. In addition, the linear topology used is based on an NPN emitter-follower with emitter resistor, which means the devices exhibit virtually no EMI, making them well-suited for sensitive applications such as medical lighting.
With a wide operating voltage range of between 1.4-40V and total power dissipation of up to 1.7W, the devices can be used to drive longer strings of LEDs while still providing sufficient protection from transients in a 24V system. Designed as monolithic solutions, the devices integrate transistors, diodes and resistors in a single package measuring 0.6mm high.
This is much thinner than the standard SOT26 package, allowing engineers, architects and lighting designers to develop LED fitments with a much lower overall profile, for a wider range of applications. Edge lighting is now being specified in areas such as emergency, mood or decorative lighting, but is equally applicable in medical, industrial and commercial environments.