Dimmer for LED retrofit using current reduction

The main purpose of this research is to design a dimmer circuit that can either be fitted with the LED itself or embedded in the switch, using the available infrastructure, such as the wiring and circuitry, thus adding new technology to older systems. The main intention in doing so is to increase energy efficiency and decrease energy consumption with the least possible expenditure. The LEDs are in theory fully dimmable but are not compatible with all dimmer controls designed for the other lighting technologies. Therefore, it is necessary that a dimmer circuit be designed in order to use them as retrofits. This dimmer design is based on the working of a resonant converter. The circuit is run at resonant frequency as maximum current passes through the load at this frequency and decreases on moving farther away. It also uses capacitors in conjunction with high frequency AC in order to balance the current in the LEDs. The LED driver circuit is based on a current-fed push-pull resonant converter. The driver circuit contains two transistors which are switched on alternatively at the resonant frequency of the circuit, thus generating the required high frequency efficiently. The two transistors are driven alternatively in a self-oscillating mode. The input to the converter is supplied through a DC rectifier with a bulk capacitor as a filter. A relatively large inductor is placed in between the rectifier and the resonant converter, in order to provide the required current supply to the converter. The brightness of the LED depends on the current passing through it and as maximum current is rendered through the load in a resonant converter, it glows at maximum brightness. On changing the frequency, the current through the load changes, thereby changing the brightness of the LED.