Thanks for the great schematics. I'm starting to work through my design for this. I'm building a current limited variable power supply and it made sense to build a constant current load first to use in testing my power supply design. (I'm building most of my non critical lab equipment as a learning experience.)
I'm working on integrating this style of current limiter with a Micro for the same Constant Current use (connected or disconnected to computer), but also measure power and source voltage. For example, you might want to setup a battery discharge at a fixed current and have the computer measure the voltage of the battery. At a certain level, you will want to switch the load off for unattended runs without completely killing the battery.
My idea is to run the positive of the source through a SPST relay (normally open) to enable the microprocessor to turn on the load after initial verification. However, I will need some sensing constantly connected to the source in front of the relay, to determine if we are good to switch on or not. My switching current on the relay can be limited, but making sure that they PWM output is setup for low current mode before contacts are switched. Is there any issue with a floating open circuit existing at the Source or Collector of the transistor, with voltage going to the base. I couldn't think of a problem, but thought I would ask.
My main issue with with source voltage measurement and input protection. This isn't really a required piece to make this work, as I can just not be a bone head (sorry, deek head) and not hook up a voltage too high. However, I thought this would be a great project to learn a little more about accurate measurement with input limiting.
I want a voltage divider and follower much like the center portion of the above schematic with the TL082. If this is sized to be just under the A/D converter max at the maximum expected incoming voltage, all is good. However, I'm trying to figure out how I would protect this. If I have an "accurate" divider/follower that should give an accurate in the expected range, but then have another that is a wider range to be safe for all expected inputs and tell if we are too high of voltage. Do I just clamp the first with a zener or something similar? I'm concerned that as we get close to the max, I will start losing accuracy due to leakage current. Or is there a method of buffering the lower voltage range A/D source that is only enabled by the micro after the sampled "always on" A/D confirms we are good to go?
Anyone have any pointers on a good resource to look at for this?