Making a simple low current limter

Sometimes you might need a constant low current to for example charge small batteries like coin cells. Often the current limit function of the power supply is too coarse to

get a reliable low current or it might not even go as low as you need. I needed to charge a coin cell package at 7 mA so I made this simple add-on board which fits directly

to a PS5004 front panel. It could be used on other power supplies too if it fits the connectors or it could be lying on the desk using lab cables to the P/S.




The board from component side. The strap selects the range and the pots adjusts the current while monitored by the DMM with 10mV/mA.



... and the reverse side.




Charging the coin cell package.



With the switch in the left position 70 mV on the DMM equals 7.0 mA charging current .... 




... and with the switch in the right position the DMM shows the actual battery voltage. The sense input is not used on the picture but if used it would provide a

more accurate reading of the battery voltage.


Schematic here 


Email me with comments. /Håkan


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