Infineon BCR112W: A Comprehensive Technical Overview and Application Note

The Infineon BCR112W is a highly integrated, low-voltage linear constant current regulator (CCR) designed for driving LEDs with exceptional reliability and efficiency. Housed in a compact SOT-143 package, this device simplifies circuit design by eliminating the need for external components typically required by traditional regulating circuits. It represents a robust and cost-effective solution for low-power lighting applications, offering superior performance and stability.

At its core, the BCR112W is a two-terminal, self-biased transistor that delivers a fixed, constant output current over a wide range of input voltages. Its nominal output current is set at 20 mA, making it ideal for standard indicator and lighting LEDs. A key advantage of this device is its low dropout voltage, which minimizes power dissipation and enhances overall system efficiency. This characteristic is crucial for battery-operated and energy-sensitive applications. The regulator maintains a stable current from a supply voltage as low as 2.5 V up to its maximum of 40 V, providing significant design flexibility.

The internal structure of the BCR112W incorporates active linear regulation. It features a built-in Zener diode that provides a stable reference voltage, which in turn controls the base of an internal NPN transistor to regulate the emitter current. This architecture ensures that the output current remains largely independent of fluctuations in the supply voltage or forward voltage variations of the LED. Furthermore, the device offers excellent temperature and current stability, protecting the LED from thermal overstress and ensuring consistent luminosity over its operational life.

Application Circuits and Design Considerations

The primary application for the BCR112W is as a simple, drop-in replacement for a current-limiting resistor. Its basic circuit configuration is remarkably straightforward: the input voltage is applied to the collector (C) and base (B) pins (which are internally connected), the anode of the LED is connected to the emitter (E) pin, and the cathode is connected to ground.

For a single LED application, the circuit requires no external components. However, for driving multiple LEDs, they can be connected in series. It is critical to ensure that the sum of the forward voltages of all series-connected LEDs, plus the dropout voltage of the BCR112W, is less than the minimum supply voltage. For parallel configurations, each LED string must have its own dedicated BCR112W to ensure current matching, as the regulators will not share current accurately if connected to a single device.

A significant benefit of using the BCR112W is its inherent over-temperature protection. As the junction temperature rises, the regulated output current gradually decreases. This negative temperature coefficient safeguards both the regulator itself and the connected LED from thermal runaway, a common failure mode in less sophisticated driving schemes.

Key Advantages and Use Cases

The BCR112W excels in a multitude of scenarios:

24V AC/DC Industrial and Automotive Systems: Its high maximum voltage rating makes it suitable for harsh electrical environments where voltage spikes are common.

Battery-Powered Devices: Low dropout voltage extends battery life in portable electronics, appliances, and handheld equipment.

Signage and Decorative Lighting: Provides a simple and reliable solution for constant current drive in multi-LED arrays.

Replacement for Resistors: Offers a performance upgrade over resistive driving, ensuring consistent LED brightness regardless of supply or temperature changes.

ICGOOODFIND: The Infineon BCR112W stands out as an exceptionally simple, robust, and cost-efficient solution for constant current LED driving. Its high level of integration, excellent stability, and built-in protective features make it an ideal choice for designers seeking to improve reliability and reduce component count in low-to-medium power lighting applications.

Keywords: Constant Current Regulator, LED Driver, Low Dropout Voltage, Thermal Stability, Infineon BCR112W