Wordpress Excerpt Function

function theme_name_excerpt($full_text, $letter_count = 50){

    $full_text = trim($full_text);

    $full_text = strip_tags($full_text);

    $full_text = strip_shortcodes($full_text);

    $full_text = mb_substr($full_text, 0, $letter_count);

    $full_text = $full_text."";

    return $full_text;

}