Abstract: In order to reduce flickering of the LED, a driving circuit with the primary side feedback control flyback converter is specifically designed on the basis of the digital technology. The principle of soft-start and the controlling flow of constant current output is deduced, the constant current control principle is given, and the internal structure of the digital controller is constructed. The setting of soft-start/constant current switching module can effectively suppress the surge current of the flyback converter and ensure that the flyback converter enters the constant current state smoothly. Based on the principle of constant current control, the demagnetization time sampling module and counter modulation module are designed, which works in coordination with the control signal generation module to automatically switching signal. Finally, the feasibility of the presented scheme is verified by the united simulation technique based on ModelSim and Simulink. The results show that the ratio of demagnetization time to switching period is constant when the flyback converter operates in constant current state, with the output constant current of about 320 mA and the current ripple of 0.38%. Consequently, the drive circuit investigated in this paper can work stably and reliably.

Key words: digital control, LED driver, flyback converter, constant current output, united simulation