Ellington has moved to Pride Park, where he will team-up again with his former boss at Wigan, Paul Jewell, on a season long loan deal with a view to making the move permanent next summer.
"I'm really excited about his move and particularly looking forward to linking up again with Paul Jewell," Ellington has said
"It's no secret that the most successful period of my career was spent playing for him at Wigan Athletic. He got the best out of me then and when I came to see him the other week he told me he intended to get the best out me again and get me scoring goals again.
"I was really impressed with the ambition of both the manager and the Chairman and excited about their plans for this coming season and beyond.
"I know they are looking to rebuild the team here and I'm looking forward to being part of that and playing my part in bringing success here."