I went to bed because i was tired

Student or Learner
I went to bed because i was tired
hi guys....most of us know that because is the correct answer.. How about if i change it to :
I went to bed AS i was tired...
Is the sentence still correct??
it's "because' . for sure
It should be 'because'since it is followed by the reason for going to bed . To use 'so' we have to say I was tired fist.
Of course BECAUSE :)