Single-Stage, Universal-Input AC/DC LED Driver With Current-Controlled Variable PFC Boost Inductor

This paper presents a single-stage flyback power-factor-correction (PFC) circuit with a variable boost inductance for high-brightness LED applications for the universal input voltage (90-270 V_rms). The proposed circuit overcomes the limitations of the conventional single-stage PFC flyback with a constant boost inductance that cannot be designed to achieve a practical maximum bulk-capacitor voltage level (i.e., less than 450 V) at high line while meeting required line-current harmonic specifications at low line. According to the proposed method for achieving variable boost inductance, the boost inductance has a constant high value at high line, while at low line it is reduced proportionally to the load current, so that the IEC 61000-3-2 class C and corresponding Japanese JIS C 61000-3-2 class C line-current harmonic limits are satisfied. The proposed single-stage PFC flyback LED driver with the variable boost inductor is experimentally verified on a 24-V/91-W prototype circuit.