Modified Harmonic Injection Technique for Electrolytic Capacitor-Less LED Driver

Conventional LED drive has a limited lifetime due to present of bulky electrolytic output capacitor (E-Cap) which is essential to make the power difference balancing between the constant output power and the pulsating input power. In fact, LED chip has a longer lifetime than E-Cap. Therefore, it is insufficient to use this type of capacitors in LED driver. Increasing the LED lamp lifetime can be achieved through changing the E-Cap with Film or Ceramic one. But the LED current peak will be double as a result of using low energy density capacitors. However, the LED can be driven by a pulsating current with a defined peak value. Peak to average ratio (PTAR) of LED current has to be limited (less than 1.4) to save LED from overdriven, failure and flux saturation. Recently, the methodology of injecting a predefined value of harmonics to limit the PTAR is costly and complex to be used in interior and exterior LED applications. This paper will present an optimization methodology for the LED driver control circuitry to be simpler and more cost-effective. Three major parameters will constrain the design of the control circuitry are cost reduction, lifetime expansion and simplicity in implementation. The feasibility of the proposed control circuit has been verified by simulation and real prototyping as well.