This is Resonant Mode LED Driver circuit. This circuit is used to give a constant DC current through a string of a given number of LEDs. This circuit uses flyback, boost, or buck topology. Each of them has disadvantages and advantages depending on the number of LEDs being driven in series, the LED output current, if dimming is required, if isolation is required, efficiency, size, cost, the number of parallel LED strings and the input voltage range. Resonant mode circuit is the new circuit that has been slightly modified from dimming fluorescent applications. Here is the circuit:

 

Resonant Mode LED Driver circuit schematic

 

The circuit can be implemented in off-line non-isolated applications. The advantages of this circuit are it can be easily scaled for different LED current levels, utilizes soft-switching for good efficiency and it can drive one or many LEDs in series.

This circuit uses IRS2530D Dimming Control IC. To drive LEDs instead of a fluorescent lamp, the output stage has been modified. The tank has been changed to a series L-C-LED type because the preheating and igniting the load is eliminated. A full-wave bridge rectifier has been added into circuit because the output current is AC. So, the current is always flowing through the LEDs during each high frequency switching cycle. [Source: International Rectifier]