I have a SSL set up on www.mydomain.com

How can I redirect traffic on mydomain.com to https://www.mydomain.com?

I've tried the following

server {
listen 443 default;
server_name _;
rewrite ^/(.*) https://www.mydomain.com/$1 permanent;
}

server {
listen 443 default;
rewrite ^ https://www.mydomain.com$request_uri?;
}

both not working..

thank's before