A cable voltage drop compensation circuit for topology of active clamp forward converters is proposed. The proposed circuit sensed load current information by sampling the CS pin at a proper moment, and then adaptively adjusted the reference voltage of the error amplifier according to the information, so the load regulation was effectively reduced and the output voltage accuracy was improved. The circuit was designed in a 0.18 μm 40 V BCD process. The simulation results show that, under 3~30 A load current range without cable voltage drop compensation, the overall load regulation of the active clamp forward converter is 9.78 mV/A, while with the proposed cable voltage drop compensation, the load regulation of the converter is reduced to 0.096 mV/A, which is only 0.98% of that without cable voltage drop compensation.