closest data sheet is:
http://www.elisnet.or.jp/download/003/2SC4637_1_3.pdf
but at Dalbani this 4637 cost is $5.95 so it seems to be quite different
from the 4641 that is only $0.19.

Anyway, this is the Sanyo data sheet search site:
http://www.elisnet.or.jp/cgi-bin/ESX/esx_service

Wagner.