The maximum collector current IC(max) of the pair is that of Q2.
A typical integrated power device
is the 2N6282, which includes a switch-off resistor and has a current gain of 2400 at IC=10 A.
Integrated devices can take less space than two individual transistors because they can use
a shared collector. Integrated Darlington pairs come packaged singly in transistor-like packages
or as an array of devices (usually eight) in an integrated circuit.
Darlington triplet
[edit]
A third transistor can be added to a Darlington pair to give even higher current gain, making a
Darlington triplet. The emitter of the second transistor in the pair is connected to the base of the
third, as the emitter of first transistor is connected to the base of the second, and the collectors
of all three transistors are connected together. This gives current gain approximately equal to
the product of the gains of the three transistors. However the increased current gain often does
not justify the sensitivity and saturation current problems, so this circuit is seldom used.
Applications
[edit]
Darlington pairs are often used in the push-pull output stages of the power audio amplifiers that
drive most sound systems. In a fully symmetrical push-pull circuit two Darlington pairs are
connected as emitter followers driving the output from the positive and negative supply: an NPN
Darlington pair connected to the positive rail providing current for positive excursions of the
output, and a PNP Darlington pair connected to the negative rail providing current for negative
excursions.
The maximum collector current IC(max) of the pair is that of Q2. A typical integrated
power device is the 2N6282, which includes a switch-off resistor and has a current gain
of 2400 at IC=10 A.
Integrated devices can take less space than two individual transistors because they can
use a shared collector. Integrated Darlington pairs come packaged singly in transistor-
like packages or as an array of devices (usually eight) in an integrated circuit.
Darlington triplet
[edit]
A third transistor can be added to a Darlington pair to give even higher current gain,
making a Darlington triplet. The emitter of the second transistor in the pair is connected
to the base of the third, as the emitter of first transistor is connected to the base of the
second, and the collectors of all three transistors are connected together. This gives
current gain approximately equal to the product of the gains of the three transistors.
However the increased current gain often does not justify the sensitivity and saturation
current problems, so this circuit is seldom used.
Applications
[edit]
Darlington pairs are often used in the push-pull output stages of the power audio
amplifiers that drive most sound systems. In a fully symmetrical push-pull circuit two
Darlington pairs are connected as emitter followers driving the output from the positive
and negative supply: an NPN Darlington pair connected to the positive rail providing
current for positive excursions of the output, and a PNP Darlington pair connected to the
negative rail providing current for negative excursions.
