LEDs driven by AC without transformers or rectifiers

We explore the driving of LEDs by untransformed AC. An extreme case is driving 1.9 V threshold (red) LEDs with UK mains, peak voltage 325 V. Commonly, driving is by transformed, rectified (DC) supply with a series resistor (where a significant fraction of the power is wasted) to limit current in the LED. With AC, one can instead reactively limit to a maximum current safe for an LED by employing a series capacitive impedance. Cheaper and simpler supplies can thus be employed in some cases. We analyse such non-linear circuits, and also explore questions of duty cycle and power experimentally.

Automated summary

The study explores the driving of LEDs by untransformed AC and how to reactively limit the maximum current safe for an LED through a series capacitive impedance when using AC, potentially allowing for cheaper and simpler power supplies in some cases. Analysis of such non-linear circuits and experimental exploration of duty cycle and power are also conducted.