Lighting
EVLIIVLED815W10A 10W , buck-boost LED driver
STEVAL-ILL055V1 11W , flyback LED driver
Fig . 2 – Main system evaluation boards
EVALIIVLED815W15 15W , flyback LED driver can be used as well ; in this topology , the 60-100V low-voltage
STripFET F7 power MOSFETs series , ensures all solutions are very efficient and reliable . The STripFET F7 family features an extremely low Rdson , an optimized body diode ( low Qrr ) and intrinsic capacitance and a proper Crss / Css ratio .
Commercial Commercial and architectural lighting applications usually they require more than 20W , a high power factor , high levels of efficiency , cost-saving solutions , and the possibility of using more than one LED string — single or multiple strings — with remote monitoring .
In the case of a single string , the flyback topology is usually used . Working in constant-current primary-side regulation ( PSR-CC ) mode , ST ' s new HVLED003D , a flyback offline LED driver controller with embedded dimming capability ( 0-10 , PWM and Triac ), can directly drive the single string without needing an optocoupler and secondary-side controller in the circuit .
For the main related switch , the MDmesh K5 power MOSFETs series is suggested , and we ’ ve found the 800-900-950Vbr part numbers fit very well . The MDmesh K5 series suits hard switching topologies , and it has a very low Rdson , and small Qg and capacitance .
The multiple strings power supply architecture consists of a main power supply ( usually a flyback ) providing a constant DC bus voltage and subsequent multiple strings . This architecture can be seen in fig . 3 .
Fig . 5 – Analog LED multiple strings management based on a controller
The suggested output diodes for buck and reverse buck topologies are the same as those reported in the single string case .
Ÿ To digitally manage the strings with reverse buck topology ( fig . 6 ) jointly to PM88 or TD35 gate drivers , ST offers the STLUX , a new series of dedicated digital lighting controllers , as well as the STM32 high-performance microcontrollers . The power MOSFETs are the same as those shown in the fig . 5 case , and the output diodes in this case are the same as those used in both figures 4 and 5 cases .
Fig . 3 – LED multiple strings power supply architecture
ST ’ s offline LED controller HVLED001 / A with constant-voltage primary-side regulation ( PSR-CV ) with dimming capability ( 0-10 , PWM ) is available for the flyback . PSR-CV means doesn ’ t need to use an optocoupler and secondary-side controller in the circuit . Power MOSFETs , output diodes and clamping net used for this flyback are the same of the ones described in the single string approach . The subsequent multiple strings can be managed using analog or digital means :
Fig . 6 – Digital LED multiple strings management
A wide offering of system evaluation boards for commercial single and multiple strings are available , and some of these are shown in fig . 7 .
STEVAL-ILL070V2 / V3 35W , analog single-string LED driver
STEVAL-ILL074V1 / V2 60W , analog power supply for LED driving
Fig . 4 – Analog LED multiple strings management based on a converter
The new HVLED0002 current mode LED controller based on a fixed off-time ( FOT ) algorithm for reverse buck topology ( fig . 5 )
STEVAL-ILL077V1 60W , digital multiple-string LED driver
STEVAL-ILL054V2 18V-4A , buck LED driver converter
Fig . 7 – Main system evaluation boards for commercial applications
ELE Times | 54 | March , 2017