I’ve got a VFD display on board along with UPD16311 driver is made for negative voltage around -30V and i think so is display (i couldn’t find any info on display) and I’m doing it mostly from junk parts. I want to know what devices could/should contain power supply for such voltage. I’ve tried -12V from psu i’ve got lying around but it didn’t work. There’s also a chance that display itself is damaged but there’s no visual sign of it.
Measured voltage is completely dependent on what is used as a reference. If you were to measure the voltage of a power supply set to +30V with a voltmeter whose leads were backwards (ie positive on the voltmeter connected to negative on the power supply, and negative connected to positive), then you would measure -30V. All this is to say that if you connect your 30V supply “backwards”, you will have -30V. Now, there may be some circuitry in the power supply that only allows current in one direction, and it could be that it’s able to source a different amount of current than it’s able to sink, so be sure to check its manual.
I’d advise caution against arbitrary decisions with electronics — both for your own safety and the safety of the equipment.
It would be weird for say, a 12V-2A PSU to not be able to source and sink 2A. The current direction didn’t change from the PSU perspective, only from the load. If you have multi-rail power supply, then yeah it may have different source-sink capabilities for different rail