Transistor activated by finger on base

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    Base Transistor
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Discussion Overview

The discussion revolves around the operation of transistors, specifically how a finger touching the base of a transistor can activate it. Participants explore the mechanisms behind this interaction, including the role of charge and capacitance, and compare NPN and PNP transistors. The scope includes conceptual understanding and technical explanations related to electronics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant suggests that touching the base of the transistor introduces charge from the body through capacitive coupling, which may explain the activation of the transistor.
  • Another participant notes that the effectiveness of this activation may depend on individual body capacitance and resistance, questioning how sufficient current can be maintained for the transistor to remain active.
  • A different perspective is offered regarding the possibility of the body picking up AC signals from mains electricity, which could influence the transistor's behavior.
  • There is a request for more information about the specific transistor model and the circuit setup to better understand the situation.
  • A link to an external resource is provided for further reading on the differences between NPN and PNP transistors.

Areas of Agreement / Disagreement

Participants express differing views on the mechanisms at play when a finger touches the transistor's base, indicating that multiple competing explanations exist without a consensus on the primary cause of activation.

Contextual Notes

Participants highlight the importance of specific circuit details and the characteristics of the transistor used, which remain unspecified. There is also uncertainty regarding the charge dynamics and the role of body capacitance in the activation process.

Who May Find This Useful

This discussion may be useful for individuals interested in electronics, particularly those seeking to understand the operation of transistors and the effects of external influences on their behavior.

mitocondrio
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So... My transistor does the switching job when I put my finger on its base. I know that NPN transistor are activated with positive charge, so... What happens between transistor, my finger and the earth? What happens to the charge? I don't know much about this, I would like an introduction.
Also, PNP transistors should be activated with a positive charge on the base... So how do them work? Please help me! Thanks :)
Thanks!
 
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You have built up some charge in your body. When you touch the base you are capacitively coupling that charge into the transistor. That's why ESD can kill electronics.

Seems like wikipedia would be a good place for you to start.
 
Hi there, well it's not that easy to imagine the specific setup you have there , well people have different body capacity and resistance , well if that is a BJT then as you probably know the current flows also from the base so unless you can make sufficient current flow the transistor should close after the current is too little to maintain emitter-collector flow.

A MOSFET could either stay open or closed depending on the charge put on it's gate but that is a different case because in a MOSFET the gate is isolated so acts as a capacitor but in a bipolar the base is part of the circuit, so where do you get the charge to put in that BJT to keep it open?
By the way it would be great if you could say the transistor part number/model.And tell more about the circuit you have.
Are you just measuring the transistor or is it in a circuit and then being measured or what?
 
Could be your body picking up the mains and acting like a AC signal injector.
 

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