Hi,
studing a little of transistor biasing history and the uses of negative feedback i find a topic i dont understand,
i attached a simple circuit with a feedback resistor inserted into the emiter side of the transistor,
i will type exactly what the book "says":
"Historically, the first attempt at stabilizing the Q point was emitter-feedback bias, Notice in the figure that an emitter resistor has been added to the circuit. the basic idea is this: if Ic increases, Ve increases causing Vb to increase.,(until here i'm fine).
More Vb means less voltage across Rb" . this results in less Ib.<-- here starts my problems:
Vb is the voltage across Rb minus the 0.7 voltage drop across the emitter diode, i'm ok?, so if originally the collector current is 20 ma and the emmiter current is +/- 20 ma, and the voltage across the Er is 3 v, this means that the Vb is about 3.7 v that is the same across the Br .i'm ok until here?.
now suppose a rise in temperature makes the Ic rise to 30ma so the Ie is about 30ma and now the Ve is 5 v, and Vb is 5.7 volts that equals Rb voltage, checking ohms law "more voltage across the resistor = more current" so why in the book the autor states: "More Vb means less voltage across Rb"
i think my confution is with the Rb voltage and the Vb.
thanks for any help and please excuse my poor english
studing a little of transistor biasing history and the uses of negative feedback i find a topic i dont understand,
i attached a simple circuit with a feedback resistor inserted into the emiter side of the transistor,
i will type exactly what the book "says":
"Historically, the first attempt at stabilizing the Q point was emitter-feedback bias, Notice in the figure that an emitter resistor has been added to the circuit. the basic idea is this: if Ic increases, Ve increases causing Vb to increase.,(until here i'm fine).
More Vb means less voltage across Rb" . this results in less Ib.<-- here starts my problems:
Vb is the voltage across Rb minus the 0.7 voltage drop across the emitter diode, i'm ok?, so if originally the collector current is 20 ma and the emmiter current is +/- 20 ma, and the voltage across the Er is 3 v, this means that the Vb is about 3.7 v that is the same across the Br .i'm ok until here?.
now suppose a rise in temperature makes the Ic rise to 30ma so the Ie is about 30ma and now the Ve is 5 v, and Vb is 5.7 volts that equals Rb voltage, checking ohms law "more voltage across the resistor = more current" so why in the book the autor states: "More Vb means less voltage across Rb"
i think my confution is with the Rb voltage and the Vb.
thanks for any help and please excuse my poor english