Nowadays the expectation is growing bigger and bigger against the electronic devices’ energy saving possibilities and compact size. A power supply with good efficiency fulfill both of these requirements. Because of the low dissipation it needs smaller cooling surface, so the devices’ size is getting smaller. In case of devices that connect to the elecrticity network, power factor is one of the determinative components of the elecrical grid's loss. This means that the power factor should be as big as possible to reach the best efficiency of the system. In my master’s thesis I would like to introduce a modular system that is designed and constructed by me. The first circuit can produce direct current with aspicious power factor and efficiency from the local alternate current, everywhere in the world. The second one uses this direct current (or can be used independently with worse power factor) to supply a 100 watts LED. Other function of the power supply is the ability to control the brightness of the LED.