improved current limiting (part2)


Now we have the control points, time to inject it into our secondary board.

Disclaimer :
It is a proof of concept and can be made much better.
In particular, it should be a low pass filter, and better impedance adaptation between the two stages.
/Disclaimer :

The control board  is based on a LM358, with two stages :
  • Amplify : So that the output range is 0--4V more or less (i'm aiming at 3.5 A max)
  • Differential amplifier : Amplify the difference between the previous stage and a reference .


The pot is there so that you can adjust the gain of the first stage, to get to the desired range.

The reference  (vRef) is just a voltage divider made by a potentiometer (so the range is 0...5v).
The differential amplifier output is fed to VOSense through a  0.1 v schottky diode.



So as soon as the current  makes ISENSE  * Stage1 gain go above  Vref, VOSENSE is driven higher than 0.8 v and the output voltage goes down.

The Vref is injected also into the ADC of an arduino so that we can display the limit.


Result:
 * A bit of ripple , not that much. Could be better.
 * It's linear, so very low current limit is hard to tune
 * Minimum current is ~ 100 mA

Next step (part3) : Software, calibration and display.


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