Electronics Engineering 2, Laboratory | Jan 23, 2018

Experiment No. 5
Darlington Pair Connection
Dan Marlo S. Bautista1, Ronnie S. Concepcion II2
1
Computer Engineering Department, University of Perpetual Help System Dalta
2
School of Graduate Studies, Mapua University
1
Cavite, Philippines, 2Manila, Philippines
1
dann8@rocketmail.com
2
concepcionriis@gmail.com

Abstract— There are certain application that require a high III. INTRODUCTION
current gain but low frequency response. In this case, a Darlington
pair connection is used. Because of its structure, two BJTs
connected, it creates a high level current output. Along with its The Darlington pair connection, named after its inventor,
high current gain it also has high input impedance when compared Sidney Darlington is a special arrangement of two standard
to a single transistor. NPN or PNP bipolar junction transistors (BJT) connected
together.[ CITATION Ele \l 1033 ]
Index Terms— BJT, Darlington Pair Connection, Phase
Difference, super-alpha pair, switching
It may sometimes also be referred to as a super-alpha pair,
but this name is used less these days. The circuit configuration
was invented at Bell Laboratories by Sidney Darlington in
I. OBJECTIVES 1953 at the time when a significant amount of work was being
undertaken into transistor development. The idea covered the
idea of having two or three transistors on a single chip where
The objective of this experiment is to be able to determine
the emitter of one transistor was connected to the base of the
the input impedance and the output impedance of an amplifier
next, and all the transistors in the Darlington configuration
using darlington pair connection and to be able to differentiate
shared the same collector.
a darlington pair and a BJT in terms of current gain.
Darlington transistor pairs can be made from two
II. MATERIALS NEEDED individually connected bipolar transistors or a one single
device commercially made in a single package with the
standard: Base, Emitter, and Collector connecting leads and are
QUANTITY MATERIALS / available in a wide variety of case styles and voltage (and
EQUIPMENT current) ratings.
1 Power Supply
1 Multimeter The Darlington pair circuit configuration is quite distinctive.
1 Oscilloscope The emitter of the input transistor is connected directly to the
1 Function Generator base of the second. Both collectors are connected together. In
Transistors this way, the base current from the first transistor enters the
1 2N6038 or equivalent (npn) base of the second.[ CITATION TDP \l 1033 ]
Resistors
1 91K Ω (1/2 W)
1 8.2K Ω (1/2 W)
2 3.3K Ω (1/2 W)
1 1K Ω (1/2 W)
Capacitors
3 10 µF

Table 1. Materials
 Electronics Engineering 2, Laboratory | Jan 23, 2018

A to 200 mV/div and the vertical scale of Channel B

to 500 mV/div. Adjust the vertical position of the two
and determine the phase difference between the input
and the output voltages.

V. ANSWERS TO QUESTIONS

1. Compute for Zi, Zo, Ai, and Av using the values

obtained from procedure 1.

24.545 uV
Zi= =45285.978 mho
Figure 1. Basic Darlington Pair configuration 0.542 nA

This results in a very high level of current gain. The overall 157.312mV
current gain of the Darlington pair is the product of the two Zo= =1652.281 mho
95.209 uA
individual transistors:
95.209 uA
Current gain total = β1*β2 Ai= =175662.362
0.542 nA
Darlington pair configuration has attributes and parameters.
157.312 mV
Av= =6409.126
1. High current gain – It has already been seen that the 24.545 uV
current gain from the Darlington pair is very high.
Figures in excess of several thousand are often seen.
2. What parameters is the main advantage of a Darlington
2. Base-emitter voltage – The Darlington pair exhibits a pair connection than using a BJT?
higher voltage between the input base and the output
emitter than a single transistor.  High current gain compared to a single transistor

3. Frequency response – Darlington pair transistor  High input impedance for overall circuit
circuits are not normally used for high frequency
applications. The Darlington pair is inherently
relatively slow because the base current for the output VI. ANALYSIS OF RESULTS
transistor cannot shut off instantly. As a result, By setting the function generator voltage to 20-mV(peak), the
Darlington pairs are generally used in low frequency Darlington pair configuration yielded a high current gain and
applications including in power supplies or areas high voltage gain. Arranging the circuit is faster as the
where a very high input impedance is needed. transistor required is already in a compact form, making the
connections much easier to configure. After setting up the
IV. PROCEDURE circuit, we recorded the data using a multimeter.

Parameters Bypassed RE Unbypassed RE

After setting up the amplifier circuit the experiment was Ii 0.542 nA 0.38 nA
conducted. Io 95.209 µA 25.522 µA
Vi 24.545 µV 3.984 µV
1. Adjust the function generator input to 20-mV(peak),
Vo 157.312 mV 28.816 µV
60 Hz frequency and measure the following ac
currents and voltages using an analog or a digital Table 2. Measured Values
multimeter. Record your data in column 2 of table 2.

2. Connect the oscilloscope probes of Channel A and

Channel B at the output terminals and input terminals
of the common-emitter configuration. Set the
oscilloscope to dual mode, and adjust the horizontal
scale to 10ms/div. Adjust the vertical scale of Channel
 Electronics Engineering 2, Laboratory | Jan 23, 2018

and effort in conceptualizing this project. He would also like

to show his greatest appreciation to his adviser, Engr. Ronn
Conception II. for the support, advices and assistance
throughout the research project. Without his encouragement
and guidance this project would not have materialized.

Figure 2. Output Waveform

The output waveform of the circuitry showed a somewhat

stable and consistent waveform. The difference is more visible
if viewed on a different vertical scale.

Figure 3. Output Waveform (small vertical scale)

VII. CONCLUSION

The Darlington pair transistor is a very useful circuit in many

applications. It provides high level current gain which can be
used in many power applications. It is mostly where high
frequency response is not needed. It can be used in audio
outputs, power supply outputs, display drivers and the like

ACKNOWLEDGMENT

The researcher takes this opportunity to express gratitude to

the people who have been instrumental in the successful
completion of this project. Especially, to those who laid time
 Electronics Engineering 2, Laboratory | Jan 23, 2018

VIII. REFERENCES
Electronics Notes. (n.d.). Transistor Darlington Pair. Retrieved from Electronics-Notes: https://www.electronics-
notes.com/articles/analogue_circuits/transistor/darlington-pair.php
Electronics Tutorials. (n.d.). Darlington Transistors. Retrieved from Electronics Tutorials: https://www.electronics-
tutorials.ws/transistor/darlington-transistor.html