LED Drivers: The Role of the Rectifier on Flicker Immunity in ELV DC Environment

Within dc operated networks, the ac-dc conversion stage in various appliances is not needed anymore and may be excluded from the design, thus increasing overall efficiency. Previous research showed that removing the diode bridge rectifier from the LED driver design can sometimes worsen and sometimes enhance the overall immunity of the LED lamp to supply voltage distortion in terms of produced luminous flicker (flicker immunity). This paper aims to explain this behavior by performing simulations of the analyzed drivers. It is found that: firstly, the voltage reference inside the driver integrated circuit is not affected by the voltage perturbations; secondly, the removal of the rectifier will not worsen the flicker immunity if the driver is properly loaded and the common mode rejection ratio is not too high in case high side current sensing is used; thirdly, the size of the smoothing capacitor does not affect the flicker immunity when dc supply is used.