Light-emitting diode driver with low-frequency ripple suppressed and dimming efficiency improved

In this study, a single-stage power-factor-corrected flyback converter is used as the main power stage, which is controlled by a critical mode control integrated circuit and is used to drive light-emitting diode (LED) strings. Since the output voltage of this converter possesses a double line frequency ripple, one energy-recycling circuit without any control is added to render the instantaneous output power close to the instantaneous input power, so as to reduce the energy stored/released in the output capacitor and hence to reduce the output voltage ripple of the double line frequency. Accordingly, the effect of the low-frequency voltage ripple on the colour, luminance, life and stability of the LED can be reduced. For the dimming circuit to be considered, the gate voltage detecting circuit is employed herein so as to achieve efficiency improvement in LED dimming. Based on the dimming command and the variation in gate voltage, the voltage reference command for the flyback converter is dynamically adjusted so as to make the voltage across the metal oxide semiconductor field effect transistor reduced as the LED string is dimmed up/down and hence to increase the efficiency of the overall system.