Should I say Ahmed or Ijaz? :o) (I think Ahmed, but please correct me if I'm wrong),

Linear Technology have lots of application notes on switching power supplies. That's a really good place to start (I did ;o) ). AN19 and AN25 are highly recommended. AN84f has a nice collection of assorted designs, including a 0 - 100V bench supply. Find them all here.

Best regards,
Rob.