Do you like the way you hit your 7-iron? Is it consistent and straight? How about driver?
I try ("try" is correct word) to hit my irons at far less than full speed. I want to control the distance more than I want more distance. The only club that I swing with the thought that "as far as possible is good" is my driver. Even so, I find that a swing thought of "swing like an athletic 90 yard pitching wedge" gives me more consistent length than swinging "hard." My regular PW distance is about 110-115 so a 90 yard swing thought is shorter and under control.
So I'm guessing your 7-iron is being swung to fast and your driver swing is tight because you are desperate to control the ball. If your 7-iron is really that fast when consistent and under control, swing a driver as if it is a 7-iron. Easy to say -- hard as heck to do.