A Primary Side Feedback Control for Flyback LED Driver with No Output Voltage Feedback Resistors

A constant average output current flyback LED driver without auxiliary windings, opto-couplers or output voltage feedback resistors is proposed. A novel on-chip feedback method through parasitic capacitor of the power MOS to detect demagnetizing time of the magnetizing inductor is used in the driver. The proposed scheme reduces the cost and improves the compaction of flyback LED drivers. The driver possesses over output voltage protection and short circuit protection on the basis of the demagnetizing time detection method. The system simulation results for a typical application show the functions of the LED driver meet the specification. Moreover, the demagnetizing time error was detected to be less than 0.6% and the average output current error is 4.43% at the worst case.