Electronic – Flip flop/latch with isolated differential input and differential output

digital-logicfeedbackflipfloplatch

I am looking to make something that takes a pulse of floating voltage (say from a feedback coil of on a transformer), and maintain a differential output voltage depending on the sign of the amplitude of the pulse. Then when another pulse comes along with a different sign, the output would change signs as well. I naturally looked into flip flops/latches, but after some experimentation and closer reading, I realized they do not really provide a differential output, and they do not seem to work with floating inputs. They seem to work instead with pulses of non-floating voltages and send a high to one of two nand/nor gates.

In summery: My problem is I am given an isolated voltage in the form of a pulse. I want something that will "remember" the sign of that pulse in the form of a voltage difference between two output leads.

The reason I emphasize the "differential" part is that the two output leads of a flip flop/latch will not form a complete circuit when connected through a load or something that senses voltage differences. It is just an open switch and a closed switch.

I may just be doing this wrong, or misunderstanding, but based on what I have tried, this seems to be nontrivial.

Best Answer

If I understand your question right, a simple centre tapped rectifier like this should do:

PulseCatcher

L1 is the primary winding, L2 and L3 are the secondary windings. OUT1 and OUT2 are to your FFs (or whatever you are capturing with) Ignore the 1Meg R3, it's just there to keep SPICE happy.
You can use the correct windings ratio to adjust the levels as desired (may be useful if high voltages are involved), and add e.g. a couple of zeners to protect your inputs. There are also many other ways to do this, depending on exactly what you are trying to do.

Simulation of above circuit (light blue is input pulse waveform, blue is negative pulse output, green is positive pulse output) EDIT - to make it clearer I simulated with a pulse file rather than a square wave as shown in the schematic:

PulseCatcherSim