PNP versus NPN bipolar transistors

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    Npn Transistors
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Discussion Overview

The discussion centers on the differences between PNP and NPN bipolar transistors, specifically focusing on the relationship between base current and collector current. Participants explore the factors influencing current gain and the implications for transistor design.

Discussion Character

  • Technical explanation, Debate/contested

Main Points Raised

  • David questions why the base current of a PNP transistor is higher than that of an NPN transistor for the same collector current.
  • Some participants suggest that the differences depend on the specific transistors, noting that current gain varies with factors like current, voltage, and temperature.
  • One participant attributes the difference to hole mobility, indicating that this results in a lower beta for PNP transistors, which in turn requires a higher base current for the same collector current.
  • Another participant emphasizes that a transistor with lower current gain will necessitate more base current for the same collector current, cautioning against general claims about PNP transistors having lower gain without evidence.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between base current and collector current in PNP versus NPN transistors, with no consensus reached on the generality of the claims regarding current gain.

Contextual Notes

The discussion highlights the variability in current gain among different transistor models and the influence of external factors, but does not resolve the implications of these variations.

cabrera
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Hi,

Could anybody explain me why the base current of a pnp is higher than a npn for the same collector current?

Regards,
David
 
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It depends a great deal on the particular transistors. Some are designed for high current, some for low, and the current gain varies with many different influences: current, voltage, temperature for starters.
Some manufacturers do make complementary pairs of transistors in NPN and PNP which are designed to match each other reasonably well, for push-pull applications.
 
The simple reason traces to hole mobility - which translates to a lower beta - which translates to a higher Ib for the same Ic value compared to an NPN.
 
A transistor which has less current gain than another will require more base current for the same collector current.

PNP and NPN transistors come in a variety of current gain versions, so you couldn't claim PNP types have lower gain without producing some evidence that this is true.
 

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