AMD Mobility Radeon HD 5000 stock driver regain Brightness

Greetings, my iMac Mid 2010 whit a Radeaon HD 5670 since the last update(stock) lost brightness control, but i upgrade via Windows update the driver and bring up the AMD Mobility Radeon HD 5000 15.201.1151.1008(driver ver) driver date 11/04/2015 with that driver regain brightness control but the performance was not so good as the original driver, i search and found Bootcampdrivers and meet the AMD Mobility HD 5670 with a huge!! performance improvement! but again lost brightness control, it there a way beside the app lighter to regain control again? could some one see what have the HD 5000 stock driver that HD 5670(mod) does not have? sorry for my English and my Newbie question.
am using Windows 10 Version 10.0.17134 Build 17134