Voltage and current regulated buck converter 0 to 35 V and 0 to 5 A

[Svele]

Hi to everyone!
I want to make buck converter as lab power supply, it has to be with voltage and currrent regulation. Voltage source is a classic 50 Hz transformer from 230 Vac to 35 V dc /5 Amps and then is connected to above mentioned converter. I have a schematic with MC34060 chip but it has regulation up to 20 V and current up to 1,5 Amps...Is it possible to modify this schematic and to have regulation of voltage up to 35V and current up to 5 Amps? Please help me to solve this problem!
Greetings from Belgrade!

 

[Svele]

I have one idea to build above mentioned buck conveter with low cost chips such as MC34063A,SG3524N, TL494CN, UC3842N, UC3843N, UC3844N, UC 3845N...Please if anybody has a schematic send it to me or post here...