Due to the power level of the LED limit, usually need to drive multiple LEDs at the same time to meet the brightness requirements, therefore, a special drive circuit to light LEDs. Resistance capacity step-down:
1. The use of capacitance in the AC impedance limit input current, to obtain DC level to the LED power supply. The structure is simple, the cost is low, the input non isolation scheme, has the security hidden danger.
Conversion efficiency is very low, can not achieve constant current control.
2. Isolated Flyback circuit: The use of flyback circuit, through the transformer on the side to generate a DC level.
Then the ripple of this level is fed back to the original edge by Optocoupler, thus the self-excited stability. This kind of circuit accords with the safety identification requirement, and the output constant current accuracy is good, the conversion efficiency is high.
However, because of the need for the optical coupling and side-edge constant current control circuit, resulting in complex system, large volume, high cost.
3. The original edge scheme: through completely in the exchange of the original control output power and current, the most accurate to achieve 5% constant flow accuracy, the side only need a simple output circuit.