Functions of resistors CONTD. (TRANSISTOR BIASING)

One of the functions of a resistor is in biasing the base of a transistor. A transistor basically needs a small base
voltage (>0.6) to make a large voltage flow through its
collector/emitter terminals. But the base of a transistor is
quite vulnerable to high currents, so a resistor is incorporated here to limit the current and provide a safe biasing voltage.

The value of the base resistor of a transistor may be
calculated through the below given formula:
R = (V – 0.6).Hfe / I,

    V = source voltage to the base resistor
    I = thecollector load current
    Hfe = forward gain of a transistor(150 nominal) and 0.6 = minimum transistor biasing voltage.

These resistors are generally of low values so that the over all performance of the circuit is not affected.


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