Buck-boost converter topology for paralleling HB-LEDs using constant-power operation

A single switch multi-inductor buck-boost converter topology is presented for paralleling LED-networks. The proposed technique is based on discontinuous inductor currents to achieve a homogenous light-distribution of parallel connected high-brightness LEDs. In contrast to the common approach of driving LED-strings with constant-current, the proposed topology supplies the LEDs with constant-power. The topology has originally been developed for automotive low voltage applications; however applications with galvanic isolations and operating off-line from a 230 V or 115 V mains supply are also possible. A prototype converter has been built and tested to proof its performance for an automotive lighting application and to verify the constant-power operation of the LEDs. The converter drives 6 parallel strings with 4 high-brightness LEDs connected in series. Experimental results demonstrate a good performance when the converter is operated in its desired operation range of discontinuous conduction mode. Measurements confirm the good performance of the converter´s constant-power operation, with maximum power deviations below 2% in the LEDs. A comparison of the common constant-current drive of LEDs to the prototype´s constant-power operation shows a slightly more homogenous light distribution between the LED strings for the constant-power approach. Furthermore, tests with different heatsink temperatures show a better brightness stability of single LEDs operated at the proposed constant-power compared to the constant-current drive.