Due to the limitation of the power level of LED, it is usually required to drive multiple LED simultaneously to meet the brightness requirement. Therefore, the special driving circuit is needed to lighten the LED.
1 resistance capacitance Buck: the use of capacitors in the AC impedance to limit the input current, thereby obtaining a DC level to LED power supply. The driving method has the advantages of simple structure and low cost, but the input of the non isolation scheme is safe and hidden. And the conversion efficiency is very low, can not achieve constant current control.
2. Isolation reverse excitation circuit: using flyback circuit. Through the transformer in secondary side produces a DC level, again through the optocoupler will ripple of the level of feedback back to the original side, and self stability. The circuit conforms to the safety requirements, and the output constant current accuracy is better, and the conversion efficiency is higher. But due to the optocoupler and secondary constant current control circuit, resulting in system complexity, large volume, high cost.
3 original plan: the original plan is to control the output of the original AC power and current, the most accurate can achieve 5% of the constant current accuracy, by the side of the simple output circuit can be. The primary side mainly depends on the feedback of the auxiliary side to control the output voltage, which is controlled by the current limiting resistance, and the accuracy of the output current is controlled by the turn ratio. The original program has inherited the advantages of isolated flyback circuit, while the structure is simple, can achieve small size and low cost.
The constant current accuracy of the original boundary is difficult to control because of the difficulty in controlling the output voltage of the transformer, which leads to the high output current drift when the primary side scheme is in the use of a low quality transformer. So, original programs through improvements increase the secondary constant current control circuit, so although more complex than ordinary original programs, but the contrast flyback scheme can still be save optocoupler, the highest price.