Exactly 5 numbers every time in php

I want to add exactly 5 random numbers to an array, but each number must be different. Here is what I have so far...

$col_B = array();

for ($i=1; $i < 6; $i++) { 
    $rand = $col_ranges['B'][rand ( 0 , 14 )]; // calls to an array of numbers
    if(!in_array($rand, $col_B)){
        $col_B[] = $rand;   
    }
    else{ $i - 1;}

}
echo implode($col_B, '<br>');