Autoswitching LED Driver

A novel autoswitching Class D converter is proposed as a means to power an LED light engine. The control system regulates the LED current by adjusting the series resonant frequency. The control transformer provides intrinsic isolation between the power converter and the 0-10 V dimming interface. An innovative thermal fold-back method limits the maximum temperature of the driver and the LED array. The autoswitching methodology and the control methodology are presented in detail. The experimental model achieves an efficiency of greater than 93% at 277 V_AC while producing 100 W of output power. The light engine is dimmable to less than 10% of the rated output current. A new miswiring protection circuit does not use a thermistor and provides excellent linearity in the 0-10 V dimming interface.