I've just found the following circuit on a board I'm repairing. There are 3 N channel mosfets and 1 P channel mosfets driving the relay coil.
The signal is provided by two 5V micro pins (labelled IO7 and IO8 on the schematic).
I'm kind of struggling to understand what makes it tick.
I've done a bit more working through the circuit and think a pulse from IO8 would latch the circuit on, keeping the relay conducting without the micro having to constantly output.
And then a pulse from IO7 would turn the relay off ? I can't figure this out - time to look at how P channel mosfets work.
Thanks for the help.
I will check the relay code tomorrow. In the meantime I have taken another look at the devices and had transposed my N and P channel devices, so now the circuit schematic looks like this
I still struggle to understand how the circuit works, so wonder why they didn't just run with something like this
The BJT could be mosfet too. R6 and R7 would need to be changed to work with the relay's coil current and the 12V supply.
circuit from https://forum.mysensors.org/post/60174
Thanks for the simulation- it looks like our posts crossed. I'll take another look at your simulation.
My question is why are 4 mosfets required in the board I'm repairing when other circuits I have found only show 2. What advantage does the extra component count bring ?