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Saturation in transistors (BJTs) - why and how

The reason you would saturate a BJT, and how to calculate base current and resistor values

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  1. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    KrisBlueNZ submitted a new resource:

    Saturation in transistors (BJTs) - why and how - The reason you would saturate a BJT, and calculating base current and resistor values

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  2. hevans1944

    hevans1944 Hop - AC8NS

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    At least one reference defines saturation occurring when the base-emitter junction is forward biased and the base-collector junction also becomes forward biased, as a result of the decrease in collector voltage. I think it does no harm to have a little "too much" base current, just to guarantee saturation does occur.... shooting for Vce in the neighborhood of 0.2 V.
     
  3. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    Right, that's the thrust of the resource - that you need "too much" base current.

    I mentioned forward-biasing of the base-collector junction as one way to define saturation, but no matter how you define it, there is no clear demarcation between "not quite saturated" and "saturated". Even if you use the base-collector forward bias criterion, I don't think it's right to say saturation "occurs" as soon as any current flows that way. Perhaps you could say it occurs when IBC reaches or exceeds IBE but that's also just arbitrary.
     
  4. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    Yeah, the transition from linear operation to "saturation" is not abrupt. Brute force is the way to go as long as you don't fry the base-emitter junction.
     
    KrisBlueNZ likes this.
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