/diy/ - Do It Yourself

im making a heinously bright led panel. they are 100w 32-36v 3 amp cobs wired up 6 in series and 3 banks in parallel. i plan on running it off the wall and 125vac rectified gives about 175vdc, so each cob is getting about 29v (undervolted for thermal management) and the whole thing draws around 9 amps.
as i found out, as these things heat up the current draw increases and leads to thermal runaway which aint no good. what is the best way to keep them under control?
hard mode: no chips or controllers, only passives if at all possible