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Author Topic: What are the advantage and disadvantage of Darlington pair  (Read 1887 times)
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hello everyone.

can you tell me What are the advantage and disadvantage of Darlington pair?
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Advantage:

Higher switching current

Disadvantage:

Multiple transistor stages means more noise, and possibly a slower response. Though this is somewhat meaningless without any specific part.


An example - you haven't given any information on purpose, so I will make up a unrealistic example to demonstrate...

For a BJT (Bipolar Junction Transistor), the current that flows into the collector is proportional to the current that flows into the base.
For example transistor x has a Beta, or current gain, of around 30. What this means is that for every 1mA that flows into the base, 30mA can flow into the collector. This is fine for smallish control signals such as that from an arduino pin. The arduino can source 20mA which means for this gain you can have a maximum collector current of around 600mA.
But what if you need to drive say 20 x 0.45A loads individually. That would require you to source ~17mA form every pin which would go far beyond the maximum power dissipation of the chip. Instead what if you used two transistors for each load. The base of the first is connected to the the arduino via a resistor to control the base current. Its collector is connected to Vcc, and its emitter is connected to the base of a second transistor. The second transistor is used to drive the load.
In this configuration lets say you put 0.5mA into the base of the first transistor. This gets amplified so that 0.5*30=15mA flows into the collector and out of the emitter from the power supply. This 15mA flows into the base of the second transistor where it is again amplified and into the second transistors collector you get 15*30=450mA.
By using this configuration for all of the loads you have cut down the amount of current the microcontroller has to source from 300mA down to 20mA, which is much better for the microcontroller.

Basically the darlington pair (or triple, or quadruple etc) allow you to get higher gains in current than a single transistor. But the whether they are needed or not depends on the application.
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~Tom~

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Advantages:- Lots of gain so a small current can drive a large load.
Disadvantages:- Two transistors give two Vbe 0.7V drops and the Vsat is twice what it could be. This causes it to dissipate more heat than a single transistor.
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Quote
can you tell me What are the advantage and disadvantage of Darlington pair?

+s: very easy to drive; cheap;
-s: high voltage drop; bulky;
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