Need regular match help - possibly

I need a routine that will allow me to trap multiple <br> and/or line feed characters and convert them to a constant number. As an example, let's say that you have text that has 10 carriage returns and/or line feeds. I want to limit this to 3. So, I need to be able to parse the line to detect the multiple control characters and convert the string to 3. So if the string looked something like: This is \n\n\n\n\n\n\n\n\n\n a test. I would want it converted to This is \n\n\n a test. Conceivably, it could be This is <br><br><br><br><br> a test. I would want it converted to This is <br><br><br> a test. I know I could write a do/while loop, but I was wondering if there is a way using eregi_replace or something along that line? Thanks!