What happens when VB > 0.7V and no remitter resistor?

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Zoner118

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I'm experimenting with a common emitter feedback bias amplifier setup, no RE, if I bias the base above 0.7V, what happens? Does VBE increase, current spike, or does something else weird happen? I am just experimenting
 
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If you don’t control the base current, the transistor will probably saturate (turn fully on). A base resistor, chosen for the collector current and the transistor’s beta, will allow you to linearize the circuit.

The gain of the amplifier will be very transistor-dependent. Feedback can give you better control of the amplifier. Have fun, and learn a bunch!
 
Zoner118 said:
I'm experimenting with a common emitter feedback bias amplifier setup, no RE, if I bias the base above 0.7V, what happens? Does VBE increase, current spike, or does something else weird happen? I am just experimenting
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If you're gonna bias the base above 0.7 then the VBE will increase, and will increase the base current too. I'm not familiar with the other aspects but @barfle here explained really good/
 
Setting the base above 0.7V without an emitter resistor can make V_BE go up a bit, which can cause the base and collector currents to increase a lot. Without RE, the transistor might get too hot or saturate. Yep, do you have a schematic to look over your setup?
 
The simple answer is it depends on the source resistance of the voltage driving the base. In the real world this will not be zero. The current that flows and the value of Vbe will be determined by the voltage, its source resistor and the transistor equation (which you can find in any good text book).

Cheers

Ian
 
Pretty simple for silicon & germanium transistors. Force Vbe more than a diode drop and the base current skyrockets. Transistor go POOF!
 

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