Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!wuarchive!uunet!zephyr.ens.tek.com!gvgpsa!gold.gvg.tek.com!grege From: grege@gold.gvg.tek.com (Greg Ebert) Newsgroups: sci.electronics Subject: Re: Transistor leakage current ? Message-ID: <1973@gold.gvg.tek.com> Date: 13 Feb 91 21:20:50 GMT References: Organization: Grass Valley Group, Grass Valley, CA Lines: 31 [circuit deleted] Icbo is collector-base leakage current with the emitter open. It is usually specified for a 'large' collector-base voltage. It is also exponentially related to temperature and approximately doubles every 8 degrees C (Ouch!). Icbo is troublesome in the sense that when you connect the emitter (ie, use the transistor in a real circuit), it will produce a collector-emitter current approximately equal to (beta*Icbo). As collector current increases, so does device heating, and thus Icbo, thus Ic... It is possible to construct a circuit which will have sufficient positive thermal feedback to self-destruct. But fortunately, you can shunt-away some/most Icb(o) by driving Vbe with a voltage source, instead of leaving the base open. As suggested in the original article, you can apply reverse Vbe bias without damaging the device if you follow the spec. I did this with a 850V/75Amp (yes my friends, thats AMPS, not mA or uA) device and its still quite healthy. - - - Though possibly off-subject, unclamped inductive loads (or improperly clamped) are the most prevalent transistor-zappers in motor/inverter circuits. Have respect for 1/2LI^2 ;if you don't provide a path for it to dissipate, it will transmute your expensive device into a fuse. ##### ## | ## # | # # /|\ # #/ | \# #######