SQL server has data files and log files, reason log files are increasing are a long running transaction running (Index maintenance)?, big transactions (i.e millions of transactions per hour)?, or your log file is in default recovery mode(i.e full)?
How to stop growing log file too big
1. Monitor default Size Limit:
In case SQL ldf file is growing too big then, put a large default size limit on the SQL server, so that it does not expands automatically and overloads the SQL server database.
2. Using the Memory Units:
Remember to configure the expansion of log files by making use of the memory units instead of percentage if the SQL transaction log file grows quickly.
3. Changing the recovery model:
Simple Recovery model helps in controlling and shrinking the log file size. Based on how crucial the data is, user can choose any of the following recovery models namely,
a. Simple Recovery Model (recommended, take decision considering to DB uses, monitoring and backup)
b. Bulk-logged Recovery Model
c. Full Recovery Model (not recommended, take decision considering to DB uses, monitoring and backup)
Check following posts for detailed explanations,