We do this by carefully choosing the emitter resistance, R E, which provides stability against differences in β. Therefore, when we are designing transistor circuits where we want roughly the same gain in all of them, we must design them in a way that produces the same gain despite fluctuations in the β values. We do this by carefully choosing the emitter resistance, R There is no way to replicate the same exact βs across transistors. of a transistor, its gain or amplification factor, can vary by large amounts from transistor to transistor, even if they’re the same exact type from the same batch. The R E provides stability in gain of the emitter current of a transistor circuit. I C≈ I E How Emitter Resistor, RE, Fights Against the Instability of β:
The collector current I C is approximately equal to the emitter current.
Then, we calculate for the emitter current using the following formula: We calculate R B below, which we will use the next calculation for I E. The base supply voltage, V BB, is calculated by: Also, voltage divider network biasing makes the transistor circuit independent of changes in beta as the voltages at the transistors base, emitter, and collector are dependent on external circuit values.īelow is a typical BJT receiving voltage divider bias,įor the circuit above, we’re going to assume that β=100 for the transistor. This voltage divider configuration is the most widely used transistor biasing method, as the emitter diode of the transistor is forward biased by the voltage dropped across resistor R B2. One way to bias a BJT transistor is a method called voltage divider bias. Voltage Divider Bias of a BJT Transistor: Voltage Divider Transistor Biasing circuit Transistor Biasing is the process of setting a transistors DC operating voltage or current conditions to the correct level so that any AC input signal can be amplified correctly by the transistor.
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