(please)help on driver rotation limitation

is it possible to limit the rotation of a bone so that it only effects itwhile going up abd not down?
example:the guy only smiles when i go up and not down(it can go down but only too an extent)
Help?:frowning:
EDIT:
never mind found the answer, thanks anyway

It sounds like youโ€™re trying to do facial expressions? Maybe you should try shape keys instead of bones?