Page 8 - EE Times Europe November 2021 final

8 EE|Times EUROPE

Harmonized Two-Stage LED Driver Systems

Simplified illustration of Infineon’s XDPL8219
controller + ILD8150 DC/DC converter IC

DC/DC constant-current (CC) buck regulator. The AC/DC PFC/flyback series of LED linear regulators that can adjust/control the regulation of
focuses on regulatory requirements such as PFC/iTHD and on deliv- the AC/DC converter. The BCR601 adjusts the feedback loop to ensure
ering a well-regulated constant voltage to the output. The DC/DC CC there is always just enough headroom across the pass element to regu-
buck regulator’s sole function is to deliver a well-regulated DC current late its desired current.
to the LED array. This system approach satisfies the designer require- Using linear regulators, traditional LED drivers would require the
ments with a minor penalty of cost and efficiency — if done correctly. design engineer to set the AC/DC converter’s output voltage to be
Infineon Technologies has released two AC/DC PFC/flyback con- greater than the worst-case LED array voltage. Worst-case (greatest)
trollers targeting these applications. The output of these devices is a voltage requirements on the LED array are present when the LEDs
constant voltage (CV) but intended to be paired with DC/DC CC regula- are cold, when they have high current density through them, and
tors for the lighting market. The lighting market has unique regulator when tolerance of the forward voltage is considered. Once the worst
needs, including exceptional PFC and low iTHD over wide operating case is determined, the output voltage is set, but typical LED array
conditions. Fast startup time and protection schemes are required in voltages would be lower than worst-case ones, and an inefficient
SSL systems. system is realized.
Infineon has developed secondary-side regulators such as the The BCR601’s active headroom control feature dynamically adjusts
ILD8150 and BCR601/602 to ensure that best-in-class dimming and the AC/DC converter’s output voltage regardless of LED count, LED
light-quality standards are achieved. They include dimming below 1% temperature, and LED current density, all of which affect LED array
and meet IEEE 1789 light-modulation regulations. voltage; the output voltage will continuously be optimized for LED
The company has designed the ILD8150 and BCR linear regulators to current regulation and efficiency.
optimize the system performance by working in harmony with the Adjusting the AC/DC voltage to be slightly greater in magnitude than
AC/DC controllers — by dynamically controlling the magnitude of the the LED array requires for proper regulation has benefits with
PFC/flyback’s output voltage depending on LED array voltage require- DC/DC CC switching regulators. Minimizing the duty cycle regardless
ments. The buck converters can dynamically optimize the system for of the topology often results in higher-efficiency systems. Infineon has
the best efficiency and best dimming possible. The traditional two- developed devices, circuits, and evaluation platforms that take a system
stage design would pay the penalty in efficiency; this inefficiency is approach to LED driver design.
easily recaptured — and the efficiency of the traditional design is often Infineon Technologies’ ILD8150 is a 1.50-A 80-V hysteretic
surpassed — with harmonized two-stage approaches. DC/DC CC regulator designed to meet IEEE1789 standards. By pairing
the ILD8150 with the XDPL8219 or the ICL8800 AC/DC converter and
LINEAR REGULATORS WITH ACTIVE HEADROOM CONTROL allowing the DC/DC converter to control the feedback loop, system effi-
Linear regulators have benefits such as ease of use, cost, and not ciency for a two-stage design can be greater than 92% with exceptional
creating further EMI noise in an LED driver. Of course, they can be an dimming performance.
inefficient solution if used traditionally. A linear regulator is an effi- Easily configurable digital AC/DC controllers, paired with DC/DC CC
cient method as an LED regulator as long as the input voltage is greater regulators designed to work in harmony, are required to meet today’s
in magnitude than the LED array voltage. Infineon has developed a and tomorrow’s quality of light and regulatory requirements. ■

NOVEMBER 2021 | www.eetimes.eu