I am looking for a very simple circuit that I can use to control the iris motor in a video lens assembly. The iris is operated by a small 12VDC motor. I would like to use an H-Bridge circuit with a pot on one input and a photocell on the other input so that the motor will rotate one way or the other depending on how much light strikes the photocell. The pot would be used as a sensitivity adjustment. Does anyone know of a good circuit that will do this? I was thinking of using transistors or an IC to do this.

 

I think you need to control both the position and the speed of the motor, don't you?

Is there a position feedback?

 

I don't think I need to control speed. No there is no position feedback. I built a simple H-Bridge with some transistors and it worked pretty good. I used a CAD protocell mounted in a black brass tube in one input and a pot in the other. When I turned the camera toward a lighter area the iris closed proportional to the light intensity which is what I wanted except that the transistors get hot. I tried power transistors but they were not very sensitive. I think the transistors were all drawing current all the time.