Analysis and Application of the Infineon BCR405UE6327 Linear LED Driver

The drive for greater energy efficiency and enhanced reliability in modern lighting systems has propelled the development of sophisticated LED driver ICs. Among these, linear LED drivers offer a compelling solution for low-to-medium power applications by providing a simple, cost-effective, and low-noise alternative to switching regulators. The Infineon BCR405UE6327 stands out as a quintessential example of this technology, engineered to deliver exceptional performance and simplicity in a compact package.

Technical Analysis and Operating Principle

The BCR405UE6327 is a linear constant current sink housed in a space-saving SOT-23-6 package. Its core function is to regulate a precise and stable constant current through one or several series-connected LEDs, independent of fluctuations in the supply voltage or the forward voltage (Vf) of the LEDs themselves. This is achieved through an integrated N-channel MOSFET and a control circuit that adjusts its operation to maintain the preset current.

A key feature of this device is its extremely low dropout voltage. This parameter, which is the minimum required voltage between the input (Vcc) and the output (OUT) pin for regulation, is typically just 200 mV at 20 mA. This low dropout is critical as it minimizes power dissipation within the IC, thereby enhancing overall system efficiency and allowing operation even when the input voltage is only marginally higher than the combined forward voltage of the LED chain.

The desired output current is easily set using a single external resistor (Rext) connected to the SET pin. The relationship is defined by the formula Iout ≈ 0.6V / Rext. This straightforward setup provides designers with immense flexibility to tailor the drive current for optimal LED brightness and longevity. Furthermore, the IC incorporates robust protection features, including reverse polarity protection on the SET pin and a high ESD tolerance, safeguarding the device during handling and operation.

Application Circuits and Advantages

The BCR405UE6327 excels in a wide array of applications, particularly where component count, cost, and EMI are primary concerns. Its typical application circuit is remarkably simple, requiring only the IC and the external set resistor, making it ideal for space-constrained PCB designs.

A common use case is in AC/DC mains-operated lighting, where a simple transformerless capacitive dropper power supply is used. In such designs, the BCR405U can be placed directly in the path of the rectified voltage to regulate the current through the LEDs with minimal additional components. It is also perfectly suited for automotive interior lighting (e.g., dashboard backlighting, reading lights) and consumer appliance indicators, where its low EMI ensures no interference with sensitive radio or control systems. The driver can also be easily dimmed by applying a PWM signal to its enable (EN) pin, allowing for dynamic brightness control.

The advantages of using the BCR405UE6327 are multifold:

Simplicity: Minimal external components reduce design time, board space, and BOM cost.

Low Noise: As a linear regulator, it generates no switching noise, making it ideal for noise-sensitive environments.

High Reliability: The absence of inductors and electrolytic capacitors, which are common failure points in switching converters, increases the system's mean time between failures (MTBF).

Excellent Line Regulation: It maintains a constant current despite variations in the input voltage.

ICGOODFIND Summary

The Infineon BCR405UE6327 is a highly efficient and simple linear constant current sink, offering outstanding performance for low-power LED driving applications. Its key strengths of an extremely low dropout voltage, simple current setting via a single resistor, and compact form factor make it an superior choice for designers seeking a reliable, cost-effective, and noise-free solution for lighting and indication.

Keywords

1. Linear LED Driver

2. Constant Current Sink

3. Low Dropout Voltage

4. BCR405UE6327

5. Electromagnetic Interference (EMI)