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How Transistors Work -- The Learning Circuit 27

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The Learning Circuit
sudo Sergeant
The Ben Heck Show

 

In today's Episode Karen discusses transistors. Rather than using a physical, mechanical switch, a transistor can act as an electronic switch, using signals to turn it on or off.  She'll go over what they are, how they work, and some types of transistors.  She'll cover Bipololar junction transistors (BJT), NPN transistors, PNP transistors, and darlington transistors.

 

The Learning Circuit 37: Community Feedback: Revisiting Transistors

Transistors eBook Part 1

Parents

  • There's some good information in this episode but there are a few things I think you might want to review.

     

    4:24 "Leaving 8.3V as your VCE." The VCE with the transistor on, assuming that there's enough collector current to pull the load right down, will be a couple of hundred millivolts, so there will be something like 8.8V across the LED and resistor.  [The collector voltage really does come down below the base voltage. Look on a datsheet for the figures for 'saturation'.] The VCE is the voltage between collector and emitter, not that between the supply and collector.

     

    4.47 The PNP behaves the same as the NPN except for all the voltages being reversed in polarity. The VBE with the transistor on will be a similar 0.7V, just the other way round (so you'd measure -0.7V rather than 0.7V). You're muddling exactly where it is you're measuring the voltages between and complicating things too much.

     

    4:57 If you were to force the Vbe to 8.3V, the dissipation in the transistor would be such that it would get very hot inside and fail.

Comment

  • There's some good information in this episode but there are a few things I think you might want to review.

     

    4:24 "Leaving 8.3V as your VCE." The VCE with the transistor on, assuming that there's enough collector current to pull the load right down, will be a couple of hundred millivolts, so there will be something like 8.8V across the LED and resistor.  [The collector voltage really does come down below the base voltage. Look on a datsheet for the figures for 'saturation'.] The VCE is the voltage between collector and emitter, not that between the supply and collector.

     

    4.47 The PNP behaves the same as the NPN except for all the voltages being reversed in polarity. The VBE with the transistor on will be a similar 0.7V, just the other way round (so you'd measure -0.7V rather than 0.7V). You're muddling exactly where it is you're measuring the voltages between and complicating things too much.

     

    4:57 If you were to force the Vbe to 8.3V, the dissipation in the transistor would be such that it would get very hot inside and fail.

Children