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[[File:Darlington pair diagram.svg|frame|right|Circuit diagram of a Darlington pair using NPN transistors]]
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In [[electronics]], the '''Darlington transistor''' (often called a '''Darlington pair''') is a compound structure consisting of two [[bipolar transistor]]s (either integrated or separated devices) connected in such a way that the current amplified by the first transistor is amplified further by the second one.<ref name="TAoE">{{cite book | first=Paul | last=Horowitz | coauthors=Winfield Hill | title=The Art of Electronics | publisher=Cambridge University Press  | year=1989 | isbn=0-521-37095-7}}</ref> This configuration gives a much higher common/emitter [[Electric current|current]] [[gain]] than each transistor taken separately and, in the case of 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]].
 
The Darlington configuration was invented by [[Bell Laboratories]] engineer [[Sidney Darlington]] in 1953. He [[patent]]ed the idea of having two or three transistors on a single chip sharing a collector.<ref name="DarlContrib">[http://andros.eecs.berkeley.edu/~hodges/DarlingtonCircuit.pdf Darlington’s Contributions to Transistor Circuit Design]</ref>
 
A similar configuration but with transistors of opposite type (one NPN and one PNP) is the [[Sziklai pair]], sometimes called the "complementary Darlington."
 
== Behavior ==
A Darlington pair is like a set of feeders with a high current gain (approximately the product of the gains of the two transistors). In fact, integrated devices have three leads (B, C and E), broadly equivalent to those of a standard transistor.
 
A general relation between the compound current gain and the individual gains is given by:
 
:<math>\beta_\mathrm{Darlington} = \beta_1 \cdot \beta_2 + \beta_1 + \beta_2 + 1</math>
 
If ''β<sub>1</sub>'' and ''β<sub>2</sub>'' are high enough (hundreds), this relation can be approximated with:
 
:<math>\beta_\mathrm{Darlington} \approx \beta_1 \cdot \beta_2</math>
 
Darlington pairs are available as integrated packages or can be made from two discrete transistors; Q<sub>1</sub> (the left-hand transistor in the diagram) can be a low power type, but normally Q<sub>2</sub> (on the right) will need to be high power. The maximum collector current I<sub>C</sub>(max) of the pair is that of Q<sub>2</sub>. A typical integrated power device is the 2N6282, which includes a switch-off resistor and has a current gain of 2400 at I<sub>C</sub>=10A.
 
A Darlington pair can be sensitive enough to respond to the current passed by skin contact even at safe voltages. Thus it can form the input stage of a touch-sensitive switch.
 
A typical modern device has a current gain of 1000 or more, so that only a small base current is needed to make the pair switch on. However, this high current gain comes with several drawbacks.
 
The basic Darlington transistor circuit is formed by taking the emitter of the input transistor and connecting it such that its emitter drives the base of the second and then connecting both collectors together.
 
== Disadvantages ==
 
One drawback is an approximate doubling of the base/emitter voltage. Since there are two junctions between the base and emitter of the Darlington transistor, the equivalent base/emitter voltage is the sum of both base/emitter voltages:
:<math>V_{BE} = V_{BE1} + V_{BE2} \approx 2V_{BE1}\!</math>
For silicon-based technology, where each V<sub>BEi</sub> is about 0.65 V when the device is operating in the active or saturated region, the necessary base/emitter voltage of the pair is 1.3 V.
 
Another drawback of the Darlington pair is its increased "saturation" voltage. The output transistor is not allowed to saturate (i.e. its base-collector junction must remain reverse-biased) because the first transistor, when saturated, establishes full (100%) parallel negative feedback between the collector and the base of the second transistor.<ref>Similarly, an [[emitter follower]] never saturates because of the 100% series negative feedback. Another example is an "active diode" made by a transistor with joined base and collector (e.g., the current-setting part of a [[current mirror]]).</ref> Since collector/emitter voltage is equal to the sum of its own base/emitter voltage and the collector-emitter voltage of the first transistor, both positive quantities in normal operation, it always exceeds the base-emitter voltage. (In symbols, <math>\mathrm{V_{CE2} = V_{CE1} + V_{BE2} > V_{BE2}} \Rightarrow \mathrm{V_{C2} > V_{B2}}</math> always.) Thus the "saturation" voltage of a Darlington transistor is one V<sub>BE</sub> (about 0.65 V in silicon) higher than a single transistor saturation voltage, which is typically 0.1 - 0.2 V in silicon.  For equal collector currents, this drawback translates to an increase in the dissipated power for the Darlington transistor over a single transistor. The increased low output level can cause troubles when TTL logic circuits are driven.
 
Another problem is a reduction in switching speed or response, because the first transistor cannot actively inhibit the base current of the second one, making the device slow to switch off. To alleviate this, the second transistor often has a resistor of a few hundred ohms connected between its base and emitter terminals.<ref name="TAoE"/> This resistor provides a low impedance discharge path for the charge accumulated on the base-emitter junction, allowing a faster transistor turn-off.
 
The Darlington pair has more phase shift at high frequencies than a single transistor and hence can more easily become unstable with [[negative feedback]] (i.e., systems that use this configuration can have poor [[phase margin]] due to the extra transistor delay).
 
== See also ==
* [[Sziklai pair]]
* [[Insulated-gate bipolar transistor]]
* [[ULN2003A]]
 
== References ==
{{reflist}}
 
==External links==
* {{US patent|2663806}}&nbsp;&ndash; Semiconductor signal translating devices. (ed., "Darlington Transistor")
* [http://www.eleinmec.com/article.asp?21 A Darlington Pair motor speed control circuit]
* [http://www.tedpavlic.com/teaching/osu/ece327/lab7_proj/lab7_proj_procedure.pdf ECE 327: Procedures for Output Filtering Lab]&nbsp;&ndash; Section 4 ("Power Amplifier") discusses Darlington pairs in the design of a BJT-based class-AB current driver in detail.
 
{{Transistor amplifiers}}
{{Electronic component}}
 
[[Category:Multi-stage transistor amplifiers]]
[[Category:Transistor types]]

Latest revision as of 20:48, 27 December 2014

So, you've mastered light beer preparing the most innovative cocktails. The recipes truly must be your own expedition. Does your recipes has brought great reviews through your surrounding people, relatives and buddies? If so, it is time to share the recipe with a lot of other people. But the question for you is how will you get it done. With the development of the technology, sharing information is becoming much easier for individuals. Numerous networks have come up which you could share your recipes with thousands other individuals. What around the people who doesn't use social media sites so much or choose to use such platform via android applications? If you do a survey, you will see that most with the people nowadays, use specialist to get just about any information. Hence, if you need to reach out to these folks, applications are the most effective medium to make use of. As you are going to share cocktail recipes, applications like cocktails apps will there be for cocktail lovers.


What does these cocktail apps include?


Numerous cocktail apps attended up recently. Some of these appsinclude recipes of popular cocktail drinks, feedback on the users and some in the reputed bartenders likewise. Some other similar apps include facts about popular bars across the city that serves some on the best cocktails, including their price menu. If you need some pointers about the food which should be served in addition to cocktails, listing of food details as well as the recipes could be accessed with your apps. Apart from cocktails, you may also get recipe specifics of mocktails likewise. Some with the popular apps that supply such information are Mixology, Speakeasy cocktails, BrewGene app, Cocktail flow, See my drink and many more.


If you are searching for Beer, apps are available that will inform you the places or bars where one can get the best cookie Recipes all time beer such as the history behind the creation of beer at the same time.


Where you can find these applications?


Use the app stores available online for by using these applications. Before seeking the app, have a look in the review section on the provided cocktails. This will let you decide about which cocktail is going to be suitable for you and also what is its recipes. At the same time, location from the bar or perhaps the club in which the best quality cocktails are served.


However, just making the search work doesn't finish your work. You need to upload your cocktail recipe if you want to popularize it. Now the question, how you will are going to practice it. Though recipe cocktails will there be and people who frequently use apps for such purpose probably have utilized it fully. Hence, you must make a new customized app which will promote your cocktail recipe all of which will let others share their views at the same time. In order to do make a customized app, you'll need professional help.


Where are you going to get professional assistance? Numerous experienced app developers will there be that works to be a freelancer. Appoint one specialized in making iPhone drink recipe apps. The appointed developer will build a customized application adding all the features that can help to promote your cocktail recipes inside app world. Once the app is developed, share your recipes and let other cocktail learn about it. However, the developed app must be promoted from the app store otherwise individuals will never come to find out about its existence.

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