A novel bridgeless isolated AC LED driver is developed, which improves LED utilization and application flexibility due to a coupled inductor inserted between the bidirectional switch and the LED module without any output electrolytic capacitor. By reducing the turns ratio of the coupled inductor, the voltage across the secondary side will be decreased so as to lessen the voltage across the LED strings and hence reduce the number of LEDs, thereby making the load design of the AC LED driver more flexible. It is noted that the coupled inductor plays a role of not only galvanic isolation but also inductor behavior as well as transformer behavior. Therefore, during the turn-on period of the bidirectional switch, the coupled inductor can transfer the energy to one LED string and store the energy simultaneously, whereas during the turn-off period of the bidirectional switch, the coupled inductor can release the stored energy to the other LED string. That is, two LED strings are conducted over a pulse-width-modulated (PWM) period for any half-cycle, implying that LED utilization is upgraded. As for LED dimming, it is realized by directly tuning the control signal for the bidirectional switch without any dimming circuit. Eventually, the basic operating principles and theoretical deductions are given along with some experimental results provided to verify the effectiveness of the proposed AC LED driver topology.
A Low Flicker TRIAC Dimmable Direct AC LED Driver for Always-on LED Arrays
