Switching regulators have higher energy efficiency, are independent of voltage, and can control brightness. However, the disadvantages are relatively high cost, higher complexity, and electromagnetic interference (EMI) problems. Common topologies of LED DC-DC switching regulators include Buck, Boost, Buck-Boost, or single-ended primary inductive converter (SEPIC). Among them, step-down structure is adopted when the lowest input voltage is greater than the maximum LED series voltage under all working conditions. For example, 24 Vdc is adopted to drive 6 LED series. On the contrary, when the maximum input voltage is less than the minimum output voltage under all working conditions, the booster structure is adopted. For example, 12 Vdc is adopted to drive 6 LEDS in series. When the input voltage and output voltage range overlap, step-down or SEPIC structure can be used. For example, 12 Vdc or 12 Vac can be used to drive 4 LEDS in series, but the cost and energy efficiency of this structure is the least ideal.
The direct drive LED by ac power source has also gained some development in recent years. In this structure, the LED strings are arranged in the opposite direction and work in the half cycle, and the LED only conducts when the line voltage is greater than the positive voltage. This structure has its advantages, such as avoiding the power loss caused by AC-DC conversion. However, leds in this configuration are switched on and off at low frequencies, so the eye might detect flickering. In addition, LED drive power protection should be added to the design to protect it from line surges or transients.

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