Primary-side feedback control IC design for flyback converter with energy saving burst mode

The advantages of the flyback converter with the primary-side regulation (PSR) are small size and high efficiency at light load. However, when the PSR flyback converter operates in burst mode, the controller is not able to sense the output information. Therefore, it is not easy to control the output voltage precisely. An integrated circuit design for AC-DC flyback converter using primary-side controller with burst mode energy saving is proposed in this paper. As the load decreases, the flyback converter operates from discontinuous conduction mode to frequency reduction mode. At extremely light load, the flyback converter operates in burst mode. With the proposed control, the burst-on time is detected by the voltage across the auxiliary winding, and the burst-off time can be estimated to control the output voltage ripple. In the proposed control circuit, a capacitor is charged by a constant current source during the burst-on time, and the capacitor voltage is transferred to a controlled current. Therefore, the required burst-off time can be obtained by using the controlled current to charge another capacitor until it reaches the reference voltage. Finally, this controller is fabricated with TSMC 0.25 μm CMOS high voltage mixed signal general purpose process. The flyback converter with the input voltage range of 90-130 Vrms, the output voltage of 15 V, and the output power of 30 W is implemented to verify the feasibility of the proposed controller.