Darlington Transistor – Using Darlington Transistor as Common Base

bjtdarlingtontransistors

  1. Why do we use Darlington pair?
  2. I've heard that we don't use it as common base. Why is that?
  3. Why don't we just develop a BJT with high beta value istead of using this structure?
  4. What are the different types of it?
  5. How can I recognize the emitter and collector of it (for example in the image below)?

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Best Answer

  1. For high current loads. BJTs are a current-controlled device, so one might not provide enough current amplification. This is called the beta value and is normally around 100-300 for general purpose transistors
  2. The base current is being amplified and projected through the collector to the emitter (in NPN). If it's common base, the current is the same through both transistors. Stacking the base of the second transistor to the emitter of the first one provides amplification in the 1000s
  3. Good point, these are expensive! Alternatives are MOSFETs which are voltage controlled and can handle high currents.
  4. NPN, PNP and Szikial pair (push pull amplifier)
  5. These are generally labelled in Darlington ICs such as the ULN2003
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