Infineon's High-Efficiency LED Lighting Solutions

In high-power general lighting applications, due to the discreteness of the forward voltage drop and heat dissipation caused by LED manufacturing, LED lighting solutions require highly accurate, efficient and reliable power supplies. This article introduces the power supply solution developed by Infineon specifically for LED lighting applications.

Infineon's LED (light-emitting diode) lighting solution adopts a two-stage topology of PFC (power factor controller) + LLC (logic link control) + linear driver, and implements feedback control. The primary stage is composed of PFC + LLC, acting as an AC-DC converter, and the secondary stage is composed of linear LED driver BCR450 + BDP947 power transistor, which serves as an LED constant current source. With the help of an 8-bit microcontroller, the solution not only has protection, dimming, intelligent control and communication functions, but also improves the efficiency of the linear LED driver.

This solution avoids the current imbalance between multi-channel LEDs encountered when using a single regulated output and the product stability problems caused by the switch-mode LED driver requiring more external components. It reduces product cost and improves stability. More importantly, the linear LED driver does not generate electromagnetic interference. In addition, this solution does not use electrolytic capacitors on the secondary side, thereby extending the service life.

A boost converter topology is used in the primary stage to provide power factor correction with the help of a TDA4863-2G IC (integrated circuit); this PFC drives a high-voltage MOSFET to provide a 400V DC output voltage.

The ICE2HS01G IC is a high-performance pulse frequency modulation resonant controller, more specifically, a half-bridge LLC resonant converter. It operates at a 50% duty cycle, supports two main gate drives, and implements a 180° phase shift. It combines a pulse transistor, a driver IC, and primary and secondary MOSFETs to step down the DC voltage.

An auxiliary flyback converter is implemented using the integrated power IC CoolSET? F3R ICE3BR4765J, a fixed frequency current mode PWM controller with integrated MOSFET. It provides 5V DC power for microcontroller operation and 12V DC power for linear LED driver operation.

The BCR450 linear LED driver is designed for high current general lighting applications with features such as high output current accuracy of ±1.5%, overcurrent protection, overvoltage protection and protection of the LED from thermal overload.

The BCR450, combined with an external power transistor BDP947, provides a constant LED current of up to 2000mA per channel. This output current can be adjusted using an external sense resistor. The solution is highly efficient thanks to the low voltage drop (~0.6V) across the power transistor and sense resistor. Using the linear LED driver BCR450, there are no EMI issues and no electrolytic capacitors are required, reducing product cost and increasing service life.

The independent multi-channel topology increases the design flexibility of LED lamps. Separating the LED drive power supply from the driver operation power supply further increases flexibility. The DC input voltage range is between tens of volts and hundreds of volts. This helps reduce system cost and improve system efficiency.

Infineon's 8-bit microcontroller monitors the voltage drop of the power transistors and sense resistors on all channels, evaluates the channel efficiency, and generates a PWM (pulse width modulation) feedback signal with a corresponding duty cycle to send to the main LLC. A simple RC filter circuit converts the PWM signal to a DC level as the reference voltage for the LLC. Based on the reference voltage, the LLC will adjust the DC output voltage. Under 48V DC input voltage conditions, this optimized output voltage can significantly improve the efficiency of the linear LED driver to 98%.

At the same time, the microcontroller provides PWM outputs (up to 6 PWM channels) to the linear driver BCR450, which supports dimming operation to adjust the brightness of the LED. It also allows individual switch control to avoid shutting down the entire power supply due to a fault in one channel.

The following lists the Infineon 120W LED Street Light Demonstration/Reference Design features:

● Dual-stage power supply topology with feedback control;

● Power supply voltage: 90 ~270 VAC;

● Output voltage: 37~48 VDC;

● Output current: 4 channels × 700 mA (maximum 8 channels, 240W);

● Power factor > 0.95;

● PWM dimming range: 25% ~ 100%;

● Overall power efficiency is higher than 91%;

● No electromagnetic interference is generated on the secondary side;

● Open circuit and short circuit protection and automatic detection.