Hello Klaus
Thanks for the reply...I am sorry for didnt mention about the input. The input is 230v ac,preffering the circuit with flyback converter....I am looking for a constant 28v,1.5a at the output using flyback topology with feedback system....i have designed a circuit with astable multivibrator for the switching purpose with in13005 power MOSFET to drive the current.were bridge rectifierand filter at the input.at the output side ,using center taping the transformer and fullwave rectification and pass it to a lm317 regulator as it deliver 1.5a at output.But this didnt deliver the hiccup current protection, feedback and also pf improvement,so I am looking forward for flyback topology,i haven't get any idea about how much frequency we have to provide in the input transformer section in order to get a desired about, I have visted different circuits using smps topology...were they are using with high frequency above 20khz..but all have different values....can you show me the simplest circuit with all these specification...