Is the AMC7135 current regulator an on/off type device?

Or can you adjust the VDD pin for regulation at some lower current? So far I have only seen the part used with VDD and Out tied together (constant current) or the VDD pin being driven by a MCU or such, which I assume is PWM driven. Are true constant current lights using a different LED driver?

It is either on or off. The Vdd pin powers the control circuitry. It is not a feedback pin.

Other constant current drivers use a variety of approaches. Some use a switching converter, others have some sort of adjustable variable linear regulator. Look at Led4Power’s drivers for an example.

great, thanks for the feedback. I was beginning to come to that conclusion based on more reading, now I know.

It’s basically just a transistor pass-element with a current limit. Ie, it’s designed to pass up to 350mA (or 380mA) by saturating, and will pull out of saturation into “active mode” if the device tries drawing more.

Think of a 65mph governor on a truck. Keep it floored, and it’ll go 65mph forever. But if you try going up a steep hill with too much of a load, of course the truck’s speed will drop. Level out, and it’ll get back to 65mph and stay there.