By completely controlling the output power and current on the AC primary side, the most accurate 5% constant current accuracy can be achieved, and the secondary side only needs a simple output circuit.
The primary side mainly relies on the feedback of the auxiliary side to control the output voltage, relies on the current limiting resistor to control the primary side current, and multiplies the turns ratio to control the accuracy of the output current.
The original-side solution inherits the advantages of the isolated flyback circuit, while the structure is simple, and it can achieve small size and low cost.
The problem of constant current accuracy of the primary side: The production accuracy of the transformation is difficult to control, resulting in a large output current drift when the primary side solution uses a low-quality transformer. Therefore, the primary side solution is improved by adding a secondary side constant current control circuit, which is more complicated than the ordinary primary side solution, but compared with the flyback solution, the optocoupler can still be omitted, and the system has the highest cost performance.