The DiodesZetex makes a high performance single stage Fly back and Buck-boost controller, targeting dimmable LED lighting application. It is a primary side regulation (PSR) controller which can provide accurate constant current (CC) regulation without optocoupler and secondary control circuitry. It is operating at BCM mode and switching at the valley which results in good EMI and efficiency. With working in constant on time, the system achieves high PF and low total harmonic distortion (THD) under universal input voltage. Primary side regulation without opto-coupler Valley switching for low switching loss Low start-up current, with high Efficiency and tight LED current variation range Tight output open voltage variation range