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66103A current limit problem

Question asked by alex001 on Mar 22, 2012
Latest reply on Mar 23, 2012 by PeterW
I am having a problem with the 66103A power supply current limit. It seems to just bypass the limit. We started off by trying to use it to sink current and found that it can only sink 10% of its rated current (4.5A), leaving us with the ability to sink 450mA. This would be fine except that you cannot set a negative current limit. The solution we came up with was to swap the high and low end of the power supply. To clarify, our setup is shown below and is as follows: We have 1 66103A set to 12V with a current limit of 1A. The force+ and sense+ are both tied to one end of a 680ohm resistor. The other end of the resistor is tied to the force- and sense- of another 66103A that is set to 0V and a current limit of 10mA. The force- and sense- of the first supply are tied to the force+ and sense+ of the second supply. My understanding is that the supplies will force the desired voltage for as long as the current is below the limit. Once that limit is reached, the voltage will fluctuate in order to maintain the current. Therefore the supply will go from constant voltage (CV) mode to constant current (CC) mode. Based on our setup, 12/680 = 17mA, but because of the 10mA current limit on the second supply, we thought that the current would read 10mA and the second the voltage supply would rise from 0V to approximately 5.2V and go into CC mode. Instead what we are getting is the current to read 20mA and the both voltages are still maintained, which suggests that current limit does not function as I described. Any help would be great. Also, we are using CVI and the functional panel functions to communicate with supplies. 

     +|         680ohm          |-
(12V / 1A)                (0V / 10mA)