I'm working on a project where I want to switch a load (utility LED light, +- 20W) using a motion sensor. The PIR can only operate at a maximum of 12 volts, while the load can be operated at a voltage between 12-36 volts. I want to power this circuit using a lead acid battery, with the light on the 'unregulated' output and the PIR regulated (with a buck converter) to something like 5V. The PIR also outputs a 3,3 volt signal, so I made a circuit to boost this to the battery voltage. I was wondering if a circuit like this would work or if the '0V' line would be different between the battery negative and the buck converter negative output.
According to the comments the ground is probably the same if some constraints are satisfied:
Non-isolated buck converter
Buck converter without current regulation, current regulated converters have a shunt at the ground line changing the voltage
Buck-boost converters have a negative (afaik) 'ground' voltage and thus are not usable