A simple control scheme for a single stage flyback with low harmonic distortion

This paper would like to propose a simple control technique which is capable of facilitating the adaptation of single-stage flyback (SSF) converters to the application of light sources of low-power LEDs. The average current mode has several advantages, such as an I/O current ripple that is only 1/2 of the critical conduction mode (CRM). This helps extend the lifetime of output capacitors while lowering the value of input EMI capacitance. Based on this, the present paper operates an SSF converter in the CCM. In addition, there are some extra circuits at the output. Two of them are the sample-and-hold (S/H) circuits, the other one is zero-point detecting circuit. They help to access the output voltage and the average value of feed forward voltage. Moreover, the extra circuits also contribute the system from being influenced by 120Hz ripple and reduce harmonic distortion of the input current.