i'm trying to guess meaning of value marked as Ube0 in datasheets. (datasheet adress: http://www.datasheetarchive.com/dlmain/Datasheets-36/DSA-700258.pdf, the transistor I want to use is Tesla KF-508). I want to regulate secondary circuit by voltage divider on base. Does this value means that max allowed voltage on base is 7 volts and I must design voltage divider to not allow more than 7 volts and current no more than 2.2 mA ?? (computed from measured parameter h21e = 233, max current that I want trought collector = 0.5 A)
UBEO is the base to emitter voltage with unconnected or "open" collector terminal.
A bipolar junction transistor has three terminals, base, collector and emitter. Whichever terminal is not connected for the rating is replaced with open when left unconnected. Hence similar identifiers for UCBO, UCEO.
UEBO = -UBEO = 7V means that the emitter voltage referenced to the base voltage can be 7V maximum. Often there is a "max" squeezed (UEBO,max) in to indicate it is a maximum rating.
If you exceed that voltage the base to emitter diode will break down (avalanche). When carefully used this mode of operation can be used as a white noise generator, when uncareful the transistor will be destroyed.