The functional safety LED driver

New state-of-the-art solution for fail-safe light

To guarantee the driver’s safety, fail-safe availability under all circumstances and in all situations is essential for LED-based lighting functions such as front lighting, turn indicators or brake lights in vehicles. Regular checks and providing the LEDs with the precise current at any time are indispensable. OSRAM Continental ensures the continuous performance of the lighting system with its LED driver CELSIUS defining a new standard.

CELSIUS precisely diagnoses and evaluates the lighting functions and takes over control in case of a system error to ensure the current through the LEDs. Even if signals are missing or the microcontrollers fail, OC’s solution maintains the critical function for the illumination of the road.

While most solutions only deal with failing microcontrollers and not with the failure of other hardware parts, CELSIUS measures at each power cycle – based on a three-level safety system.

At the first level, the LED driver tests itself, its safety mechanisms and its operating infrastructure and quantifies the environment from the hardware to the LED. At the middle level, the software algorithms assess the quantification according to its regularity and start operation. At the upper level, CELSIUS observes whether the software system is still functional.

With this three-level approach, OC ensures that the system works either in full operation or at least in a fail-safe state to guarantee that the driver and their environment have continuous light in every situation.

Driving testability

during operation and in production

Light is one of the most important requirements for safety. For this reason, the circuitry responsible for the accuracy of the current and thus the light must be tested during each individual operation.

To achieve this, OC has defined a self-test to check the critical infrastructure such as the power comparator and the watchdogs as well as the mathematical unit inside. Furthermore, routines measure internal quantities such as references or external components, for example, the current shunt and the inductor. Finally, all external components around the LED driver are validated.

In addition, the stored data is verified with a checksum. OC defined a CRC-16 over only 16 bytes, which allows a Hamming distance of 6 bits.

Since all these functions are measured at the beginning of a regular operation, the test results can also be used for the production plants, resulting in faster test times and reduced test equipment.

Driving flexibility

for a reliable performance

Whether turning the light on and off very smoothly, changing the load point of a feedback control system, changing the number of LEDs or the physical behavior of the circuit, modern solutions require dynamic lighting functions.

This flexibility calls for a wide range of stable operating conditions without the need to adjust the regulation loop in parallel. With eight patents inside, CELSIUS, OC’s Functional Safety LED-driver, works reliably under all conditions.