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This paper proposes a high-precision primary-side regulation constant voltage (CV) and constant current (CC) ac–dc converter. CV output is achieved by adjusting the switching frequency and primary peak voltage simultaneously, for better dynamic adjustment ability. In order to improve CV precision, a cable compensation module is adopted to inject current to pull-down resistor of auxiliary winding divider, compensating the cable voltage loss caused by the output cable resistance. On the other hand, CC output is acquired by maintaining the ratio of switching frequency and output voltage constant. The inductance compensation module regulates further to keep the product of demagnetization time and switching frequency fixed, equalizing the inconsistent output current result from the big tolerance of the transformer primary-side inductance in the same batch. Moreover, an improved demagnetization time detector is proposed, which is beneficial to raise CC precision. The control chip is implemented based on TSMC 0.35-μm 5-V/40-V BCD process, and a 12 V/1 A prototype has been built to prove the proposed control method. In CV mode, the deviation of the output voltage is within ±1.5%, while that of output current is within ±3% in CC mode. [ABSTRACT FROM AUTHOR]