I am using a 4S LIPO-battery and a commercial constant current LED driver to drive a LED setup. Data Sheet for the driver
To avoid abusing the LIPO battery, I would like to build a low-battery cut-off using the driver's on-board dimming input. The driver has both PWM and analog dimming inputs.
As for analog dimming input, the signal voltages are as follows:
0 … 0.2V -> the driver shuts off (battery voltage 13.0 or below)
0.2V … 1.3V -> dimming in function (battery voltage 13.0 … 13.5V)
1.3V … 8.0V -> LED driver in 100 % (battery voltage 13.5V or more)
What kind of circuitry would solve my case here?
Thanks!
Best Answer
I think a one or two channel op-amp and a precision voltage shunt would be your friend here. for the shutoff, simply make a voltage divider that at 13.0V, would output an equal voltage as your voltage shunt. Connect that voltage into the one input of the op-amp and the voltage regulated by the voltage shunt to the other. Connect the op-amp output to the PWM dimmer. That will take care of the low-voltage drop out.
The "work" on this circuit will be primarily in finding a particular op-amp and resistor combination to create a dimming profile that you like. (I.E. does it dim the right amount at 13.2V, 13.3V, etc.) To be clear, I am using the term "op-amp" loosely to include comparators and similar op-amp variants.
Additionally, if you want to ensure that everything is 100% on at >13.5V you can use a 2nd op-amp and a second voltage divider similar to above but with reverse the hookups to the op-amp so that it switches on at higher voltages and off at lower.