String data to blob column in update query for oracle

Question

I want to execute update query to update blob column. Query is something like this :

update table_name set blob_col = 'large text here';

But when I execute this, I get error saying :

SQL Error: ORA-01704: string literal too long.

I saw somewhere when I googled about this to use

update table_name set blob_col = utl_raw.cast_to_raw('large text here');

But for this also, I'm getting same error SQL Error: ORA-01704: string literal too long.