Hi There,
I have a problem understanding the function of a circuit I have created in LT spice.
Background: My intention was to create a constant current limit with the linear regulator LT1083. This regulator has current limiting built in and it can handle current up to 7.5Amps. If you gang two together (as per the datasheet including 0.015Ω resisters for load balancing) it will current limit if more than 15 amps is reached.
I have used an AD8211 current sense IC (model from Analog) and am sensing the input of the LT1083s intending to limit the current sensed before the LT1083s. I got this idea from a series of video blogs on a
power supply by David L. Jones on his blog EEBlog.
The problem I am facing and which has been alluded too in a reply to a post on the LT forum I made last night is that the LT1083s limit current is based on input voltage to output voltage. I don't understand this properly and how it impacts what I am trying to do.
You can view my circuit working and see that I have placed a load of 1Ω. I have an input of 30 volts and I am setting the LT1083s to 28.8 volts via the input of a voltage on the ADJ pin of 27.5V+1.3V=28V.
However, in the second trace from the bottom you can see that i_select and i_measure instead of being together here (i_select should limit i_measure using the BC547) i_measure is way lower than i_select because the LT1083s are doing their own current limit and I dont know why. What am I missing here?
Could someone please explain why this circuit isnt working and what I need to do to make the constant current limit sub circuit take control of this..
Kind Regards
Simon