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tsopa: That .pdf you posted seems to have been written by someone who never actually worked with a transistor before in his or her life.
The hie of a transistor is never anywhere near the 3k, 1k or 1.4k values given in the examples.
These values are ABSURD.
In reality, it is a fraction of an ohm, so low it is negligible. It is a miniscule fraction of the impedance shown by the emitter resistor multiplied through the hfe of the transistor, or even in comparison to the value of the base limiting resistor. That's why it's not in the spec sheet - it is so trivially low it can safely be ignored.
The base-emitter drop is never much more than .7V. If it was anywhere NEAR those values it would be much higher.
The formula Zb = hie + (1 + hfe) RE gives you the increased input resistance at the base node for a BJT with negative feedback due to an emitter resistor RE.
Section 3.3 of tsopa's pdf file reference shows an hie values lower than the emitter resistor itself. Trying to include RE (not an intrinsic part of the transistor's h parameters) won't even excuse this.
Go hook up a transistor like I said. See if you can measure anything like 1k in the B-E junction.
tsopa: That .pdf you posted seems to have been written by someone who never actually worked with a transistor before in his or her life. The hie of a transistor is never anywhere near the 3k, 1k or 1.4k values given in the examples.
These values are ABSURD.
In reality, it is a fraction of an ohm. It is negligible compared to the impedance shown through the base by the product of the emitter resistor multiplied by hfe, and negligible in comparison to the value of the smallest base limiting resistor you will probably ever use. That's why it's not in the spec sheet - it is so trivially low it can safely be ignored.
i was reading a book on audio power amplifier design a few years back, and something that stuck with me is that a well designed amplifier makes use of semiconductor physics for it's operation, and minimizes the effects of individual device characteristics. that works ok for an op amp or power amp, but with a single transistor gain stage, you are stuck with calculating the individual device characteristics...
The voltage gain is the collector resistance (in parallel with the load resistance) divided by the internal emitter resistance (plus emitter resistor value).