loose-electron
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San Diego California
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The resistance in the base serves to limit base current into the transistor, so that you do not burn out the Vbe junction. Without the resistor, you are essentially forcing a voltage onto a diode. Putting 3V or 5V logic swing into a diode makes for lots of current and "poof" fried transistor.
A resistance in parallel with the collector to emitter nodes of the transistor - Depends on the application. Some things may want an output that has a maximum and minimum resistance, depending on state control.
A resistor between the base and the emitter of large value? Thats a little unusual. It would allow current division between the Vbe junction and the resistor, and in the right ratio with the resistor in series with the base, reduce the voltage swing into the base. That would help keep the transistor out of saturation (bipolar version, not MOS, they are different) and allow the bipolar transistor to change state a bit quicker (no longer needs to recover from saturation.)
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