In LED lighting applications using AC-DC power supply, the power conversion building blocks include diodes, switches (FET), inductors, capacitors, resistors and other discrete components to perform their respective functions, and pulse width modulation (PWM) regulators to control the power conversion. Isolated AC-DC power converters usually include flyback, forward, and half-bridge topologies. Flyback topologies are the standard choice for low and medium power applications where the power is less than 30 W, while half-bridge topologies are best suited to provide higher energy efficiency/power density. As far as transformers in isolation structure are concerned, their size is related to the switching frequency, and most isolated LED drive power sources are basically "electronic" transformers.
In THE APPLICATION of LED lighting using DC-DC power supply, the driving methods of LED can include resistance type, linear voltage regulator and switching voltage regulator, etc. In resistance driving mode, the forward current of LED can be controlled by adjusting the current detection resistor in series with LED. This driving mode is easy to design, low cost, and has no ELECTROMAGNETIC compatibility (EMC) problems. Its disadvantages include voltage dependence, binning LEDS, and low energy efficiency. Linear regulators are also easy to design without EMC problems. They also support current stability and overcurrent protection (fold back), and provide external current set points. The disadvantages are power dissipation, and the input voltage is always higher than the forward voltage, with low energy efficiency. The switching regulator continuously controls the switching on and off (FET) through PWM control module, and then controls the current flow.

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