[DC Electrical Distribution: Latch randomly working]

Thread Starter

Gaspard PS (zadrenalin)

Joined Nov 25, 2017
Hi everyone,
I am working on a project of electrical distribution to clients thanks to a 12V Battery. I have to make an electronical protection against overcurrents.
I am currently testing the following circuit: (SEE Image 1)

I am measuring the intensity of the circuit in a small resistor (Shunt component n° 1) of 15 mOhms, amplify it (component Amplifier n°2), and compare it to a reference voltage. If Amplified Shunt voltage is greater than reference voltage, the latch output (component n°3) switches to 0V and keeps this voltage until I sent a new command of 5V to this latch. If latch output is 0V, latch command is 0V also thanks to the diode (I have "memory" of overcurrents). The "AND" (component n°4) then enable a MOSFET to conduct current if latch output is High.
My latch is randomly working. Sometimes the output of the latch switches to 0 in case of overcurrent and stays there.
Here in blue is latch input, in green latch command, in red latch output.

In other cases of overcurrents, latch output switches to 0V and then 2 microseconds later strangly switches again to 5V! This happens during 8 microseconds (the time the overcurrent peak ends) Thus overcurrent's protection is not working...

Here in blue is Shunt voltage measure , in Red Input- of comparator, in green latch command, in yellow latch output (Input- = Vref at the time where latch switches to 0V).

Would you have any idea of what's troubling the latch ? I am running out of new ideas...
Don't hesitate if you need further information
Thank you for your help ! :)
I give you the datasheets
LMC6482 (amplificater) http://www.ti.com/lit/ds/symlink/lmc6482.pdf
LM 393N (Comparator) http://www.ti.com/lit/ds/symlink/lm393-n.pdf
SN74LS375 (latch http://www.galigear.com.au/pdf_files/74LS375_datasheet.pdf
CD4081b (AND) http://www.ti.com/general/docs/lit/getliterature.tsp?genericPartNumber=cd4082b&fileType=pdf