It is very difficult to design a converter with PF exactly equals to 1, but you can design a AC-DC converter with power factors a little less that one, e.g. PF = 0.98.
To design such converter, you must use a PFC (power factor correction) unit in the first stage of your converter:
AC line ---------> PFC-------------> converter
Please give more detail information about the converter you need:
Input AC voltage:?
Output DC Voltage:?
Output Power:?
i dotn think we can attain the unity power factor
as there will be tolerances in the componenets used
but you can achieve a little less then unity almost .98 and .99
i am using a pfc ic of texas make ucc2818d
and a lot of ics are available
but you should use it after the bridge as the first stage