Dimmable AC LED driver with efficiency improved based on switched LED module

In this paper, one AC light-emitting diode (LED) driver with high power factor (PF) and low total harmonic distortion (THD) is adopted, which is added with the proposed switched LED module and is controlled based on the field-programmable gate array (FPGA). By doing so, the efficiency of such an AC LED driver can be improved significantly. This switched LED module is constructed by several LED strings, which have individual series-connected MOSFET switches. As the switch of the switched LED module is turned on, the corresponding LED string is short-circuited and hence is not conducted, whereas as the switch of the switched LED module is turned off, the corresponding LED string is conducted due to the redundant input voltage across this LED string. Therefore, the redundant input voltage across between the collector and emitter of the BJT current source can be reduced, that is, the unwanted power dissipation in the BJT current source can be decreased, so as to upgrade the efficiency of the overall system.