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Darlington Pair
f-alpha.net » Electronics » Basic Circuits » Darlington Pair » Let's go... » Experiment 4 - Darlington Pair III

Experiment 4 - Gain of the Darlington Pair

Build the circuit shown. With two multimeters you measure the current into the base of transistor T1 and the collector current of the Darlington pair.

Measuring the gain of a Darlington pair. (Enlarge)

Circuit diagram measuring the gain of a Darlington pair.

You'll have difficulty to measure a current into the base of transistor T1 at all. Turn the potentiometer P1 to a point where the Darlington pair is not yet saturated and you might measure the following currents...

IB = 0.1 μA         IC = 4.0 mA

Hence the gain βD of the Darlington pair calculates...

βD = IC ÷ IB = 4.0 mA ÷ 0.0001 mA = 40,000

β of the Darlington Pair

The gain βD of the Darlington pair is approximately the product of the gains of the individual transistors...

βD = βT1 × βT2

(You derive this formula in Experiment 16...)

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