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Using the capacitance's impedance at AC to limit the input current, the DC level is obtained to power the LED. This kind of driving method has simple structure and low cost, but the input of non-isolation scheme has security hidden trouble. And the conversion efficiency is very low, can not achieve constant current control.
Isolated flyback circuit
A flyback circuit is used to generate a DC level on the secondary side through a transformer, and then the ripple of this level is fed back to the original side through an optocoupler, thus achieving self-excited stability. This kind of circuit meets the safety requirements, and the output constant current precision is better, and the conversion efficiency is higher. However, due to the need of optocoupler and side constant current control circuit, the system is complicated, large in volume and high in cost. At present has been gradually replaced by the original edge scheme.
The original edge solutions
The original edge scheme is to control the output power and current completely on the ac original edge, and the most accurate constant current accuracy can be achieved at 5%. The secondary edge only needs a simple output circuit. The original side mainly relies on the feedback of the auxiliary side to control the output voltage, the current of the original side is controlled by the current limiting resistance, and the accuracy of the output current is controlled by multiplying by the turns ratio. The original edge scheme inherits the advantages of isolated flyback circuit, and at the same time, its simple architecture, small size and low cost make it become the mainstream driver at present.
Constant current accuracy of the original edge: Due to the difficulty in controlling the production accuracy of the transformer, the output current drift of the original edge scheme is large when the low-quality transformer is used. Therefore, the side constant current control circuit is added through the improvement of the original side scheme, which is more complex than the ordinary side scheme, but compared with the flyback scheme, the optical coupling and so on can still be eliminated, and the system has the highest cost performance.
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