A full database backup does not truncate the log. If you don't take regular transaction log backups, the log file continues to grow until it runs out of space. ... To reduce the size of the transaction log file, you need to shrink the log file.
Does backing up a SQL database shrink the log file?
Backing up your database (FULL, DIFFERENTIAL) does nothing with the TLog files. A FULL backup will create a consistent state of your database together with the committed transactions form the TLog file.
Does a full SQL backup include transaction logs?
A full database backup backs up the whole database. This includes part of the transaction log so that the full database can be recovered after a full database backup is restored.