i think its the same way thats exactly it i dont feel the muscles controling it on the way down i dont feel my back squeezed i dont feel my triceps locking out etc..
im doing 15-30 reps circuit training for two weeks.
How are you doing those 15-30 reps? quick and explosive? Or like normal reps, just doing more per set. if you are just doing them quick and pumping, then you might be to focused on getting the set done quickly and not focusing on form.
You should get someone to help you with a proper bench form/setup. Shoulder blades back, feet tucked back slightly, slight arch in lower back, not huge arch. I don't think you should lock out your triceps at the top, it shifts weight and force down through your joints as opposed to your muscled holding the weight. If you are feeling it in your chest, that's good. That's what you want. Slow your reps down if you have to, it sounds like you are dropping the weight b/c you feel like you need to blast through the set as fast as possible. You can do high reps, with some speed, BUT you still have to keep your form and technique correct. Not just get it done no matter what.
Also, if you can, get a buddy to video you with his cell, of you doing a set just like you did before this post. Do the same thing, weight, reps, speed. Post it up so we can see, and so you can see it from an outsider's perspective. It's hard for you to see what's going on really since all you look at is the ceiling.