I want to get:
So it looks as if the basic pattern you're after is "A(digits)+B(digits)"
Your expression seems a bit over-complicated for that purpose, I'd simply use:
preg_match('/^A\d+(\+B\d+)+$/', $input, $match);
If the input can be alphanumeric (A(alnum)+B(alnum), just use
preg_match('/^A[:alnum:]+(\+B[:alnum:]+)+$/', $input, $match);
Basically, the 2 absolute hard requirements are: the input string should start with an upper-case A, and there should be one + sign, followed by an upper-case B. Whatever the characters in between should be, you just have to add a character group that best fits your requirements. From the examples you gave
\d+ (one or more digits) seems to fit the bill. If "A00FF33+B123ABC" should be valid, I'd either use
[0-9A-F] (for hex values) instead.
The trick for the one-or-more requirement is to create a group for the +Belement part of the match, and repeat that group one or more times:
\+B\d+ //matches once (\+B\d+)+ //matches once or more