High-efficiency multiple LED-string driver for street lighting and TV backlighting applications

This paper describes a soft-switched high-efficiency multiple current source well-suited to drive multiple strings of LED in street lighting, TV backlighting and, more in general, Solid-state lighting (SSL) applications with electrical isolation. This topology enables a simple overall architecture with only two conversion stages from the ac line to the LED strings, PFC pre-regulator included. LED current can be accurately controlled with PSR (Primary Sensing Regulation), thus no optocoupler is needed and reliability is enhanced. Additionally, each LED string can be dimmed (either PWM or linear) independently from the others. In particular, PWM dimming can go down to very low duty cycles with excellent cross-regulation and dynamic response.