Figure 4 BD555BKFV Block Diagram.
For full resolution click on image.
The curve after which the conversion of in the phase angles in LED currents takes place, is adjusted by an internal logarithmic adaption to the sensitivity curve of the human eye, thus delivering a pleasantly smooth and natural dimming performance. A pulse width modulation controller or a linear DC signal may alternatively replace the phase angle. An intelligent, on-chip power management system with low startup current and low operating current also controls the start-up and normal operation for optimized system energy consumption. The soft start behavior can be defined with the same capacitor which is also used for dimming detection
With the new LED driver family, the user can choose between different, simple to sophisticated power supply options to achieve maximum energy efficiency. He also receives a variety of configuration options, such as adaptation to 240V or 100V power grids, HB-LED configurations and adjustable soft start or emergency light functions. In addition, a wide range of external HV semiconductors is supported.
Various protection circuits such as the bleeder control, under voltage lockout, -and protection against over current (induction saturation), short circuit and overheating ensure reliability and fault tolerance. Customers expect a much longer lifetime from LEDs than from standard lamps which also justifies a higher purchase price. These integrated features help to achieve this goal without major development effort. A protective mechanism against the false activation of the LEDs by a leakage current is included as well. With an operating temperature of -40 to +110° C, the drivers cover a wide range of application areas.
The LED driver family BD555 is a flexible building block solution for demanding dimmable LED lamps, and not only creates the conditions for the design of highly efficient systems with low power consumption, but also gives the designers the chance to abandon expensive and complex multi-component solutions.
About the author
Raimund Wagner is Product Manager LED drivers at ROHM Semiconductor GmbH
Courtesy of EETimes Europe