The PS30, a constant duty cycle 67 kHz LED driver from Supertex, is optimized for dimmable off-line LED bulb/tube applications, providing high power factor correction (PFC). The PS30 is intended to drive a single switch, single inductor power converter (flyback for isolated version and buck-boost for non-isolated version) directly from AC line, 110 V or 220 V, for power levels up to 20 W. PS30DB1 demo board provides a 6.3 W design solution, achieving 93% PFC and greater than 81% efficiency with ±4% current accuracy. It can be modified for other power levels up to 20 W.
PS30 offers smooth dimming to extinction for a wide variety of dimmer types such as leading edge dimmers, trailing edge dimmers, and dimmers with microprocessor controls. It implements a PFC LED driver solution, operating from a 10V shunt regulator derived from the power supply snubber, and provides for a simple design by eliminating feedback components and the optocoupler typical in isolated solutions. It minimizes line induced brightness variation, and protects against open circuit failure with over voltage protection.
Two unique features, covered by filed patents, enhance the performance and value of PS30. It is designed to implement a simpler, lower cost open loop solution. The potential limitation of open loop design is that the output choke tolerance normally results in variation in output current amplitude across product builds in production. PS30 includes proprietary control techniques that largely mitigate this output current variation. It also includes proprietary dimming circuits that ensure proper operation with different triac dimmers. It controls the timing of the power stage and activation of auxiliary loading to eliminate concerns of erratic SCR firing and the resultant flickering. Its circuitry ensures stable operation during light load conditions and a consistent starting point for the zero crossing phase detection.
