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How do you design a voltage divider bias circuit with certain specifications for Vcc Ic and beta-dc?

Answer:

When you design a voltage divider bias circuit for a BJT amplifier, you must consider the base current, because that represents a resistance which is in parallel with the lower leg of the divider.

To determine the base current, select the desired operating point, and calculate the emitter (collector) current. Divide that by beta-dc, and you have base current.

Back calculate the effective base resistance, and build the divider accordingly. Note that in a silicon BJT, the base voltage is about 0.7 V higher (NPN) or lower (PNP) than the emitter. Note also that these calculations only work correctly when the BJT is in linear mode. Note also that beta-dc varies amongst BJT's, even though with identical designs, so your design must consider these variations - you can compensate with an emitter resistor, but variations still have an impact.

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First answer by Alex146. Last edit by Alex146. Contributor trust: 419 [recommend contributor ]. Question popularity: 2 [recommend question].

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