A method of biasing a transistor for linear operation using a single-source resistive voltage divider. This is the most widely used biasing method.

Up to this point a separate dc source, V_{BB}, was used to bias the base-emitter junction because it could be varied independently of V_{CC} and it helped to illustrate transistor operation. A more practical bias method is to use V_{CC} as the single bias source, as shown in the above Figure.

To simplify the schematic, the battery symbol is omitted and replaced by a line termination circle with a voltage indicator (V_{CC}) as shown. A dc bias voltage at the base of the transistor can be developed by a resistive voltage-divider that consists of R1 and R2, as shown in Figure. V_{CC} is the dc collector supply voltage. Two current paths are between point A and ground: one through R2 and the other through the base-emitter junction of the transistor and R_{E}. Generally, voltage-divider bias circuits are designed so that the base current is much smaller than the current (I2) through R2 in Figure.

In this case, the voltage-divider circuit is very straightforward to analyze because the loading effect of the base current can be ignored. A voltage divider in which the base current is small compared to the current in R2 is said to be a stiff voltage divider because the base voltage is relatively independent of different transistors and temperature effects.

To analyze a voltage-divider circuit in which I_{B} is small compared to I2, first calculate the voltage on the base using the unloaded voltage-divider rule:

Once you know the base voltage, you can find the voltages and currents in the circuit, as follows:

Once you know V_{C} and V_{E}, you can determine V_{CE}.

**V**_{CE} = V_{C} – V_{E}

_{CE}= V

_{C}– V

_{E}

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#### Engineering Tutorial Keywords:

- voltage divider bias circuit