TABLE OF CONTENTS Robert A. Pease
| Note | This V BE topic has come up many, many times since junction transistors were introduced in the 1950s. Usually scholars like to use lots of exponential equations, and they seem to pretend that IS is constant. Then they show the old, trite curve where Ic bends like a hockey stick at V BE = 0.6 volts on a linear-linear scale. They pretend the transistor has no collector current below V BE = 0.4 volts. This does not help a user or engineer understand how things change versus Ic or temperature. They ignore the way that the transistor's current shrinks exponentially, all the way down to just a few millivolts of V BE, and does not magically stop below a certain "threshold." This analysis helps me a lot; how about you? Bob Widlar used graphical techniques to design transistor circuits that ran some transistors on a small number of nanoamperes or of millivolts./rap |
The other day, I was walking past the applications engineering area when I heard a grouchy debate between a couple of guys over in the corner. As they saw me walk by, they called out, "Bob, come on over here, and maybe you can solve this problem for us." I looked at their problem.
"Bob, we were trying to use the standard diode equation to compute the tempco of a transistor's V BE, and it doesn't seem to make any sense." I looked at their standard equation:
