Due to the limitations of LED power level, it is usually necessary to drive multiple LEDs at the same time to meet the demand for brightness, so a special drive circuit is needed to light the LEDs.
1. Pressure reduction: The use of capacitance in the AC impedance to limit the input current, thereby obtaining DC level to the LED power supply. This kind of drive is simple in structure and low in cost, but the input is not isolated, there are security risks. And the conversion efficiency is very low, can not achieve constant current control.
2. Isolation flyback Circuit: The use of flyback circuit, through the transformer on the side of the secondary generation of DC level,
Then the ripple of this level is fed back to the original edge by Optocoupler, thus the self excitation is stable. This kind of circuit accords with the requirement of safety identification, and the output constant current precision is good, the conversion efficiency is high. However, due to the need of optical coupling and auxiliary edge constant current control circuit, resulting in complex system, large volume, high cost.
3. Original Edge scheme: The original edge scheme is through the total control of the original side of the output power supply and current, the most accurate can achieve 5% of the constant flow accuracy, the side only need a simple output circuit can. The original edge mainly relies on the feedback of auxiliary side to control the output voltage, and relies on the control of the current of the limiting resistor to the original edge, and the accuracy of the output current by multiplying the ratio of the turn. The original edge scheme inherits the advantages of the isolation flyback circuit, while the architecture is simple and can achieve small size and low cost.
The constant flow accuracy problem of the original edge: Because of the difficult control of the production precision of the variable pressure, the output current drift is larger when the original edge scheme is used in the low quality transformer. Therefore, the original edge scheme by improving the auxiliary edge constant current control circuit, which is more complicated than the common original edge scheme, but compared with the flyback scheme, can still save the Optocoupler, the system cost-effective.