One of the solutions is to connect another supply conventor in series with the main power supply, it forces the power supply closely follow the sine type line voltage to get the current. Figure 9 is the principle diagram.This solution is suitable for the products which is directly powered by the high voltage rectifying way.
Power frequency AC will change into the fluctuant dc after the rectifying of the rectifier, the fluctuant dc powers the PFC for switching the circuit. For the common switch power supply, since PFC control circuit is equivalent to increase a level switch circuit between the rectifiers and filter circuits of the original switch power source.
On one hand, it increased the degree of the complexity of the circuit, the power section of the original system may need to be redesigned and layout. On the other hand, it is equivalent to increase a level switch circuit, the radio-frequency disturbance produced by the power supply may be increased and even exceed the standard. Then, you need to take some measures to make it meet the requirement of the related standards.