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Hi, i'm just trying to understand the transistor specifics on circuitlab but i confused on the saturation current. For example, if you check the BC547B you'll find a value of 1.53e-14 A (a very little current) but on the datasheet i found the value of 100 mA. What is the reason of this difference? Maybe these is a different measure i'm missing?

Thanks

Thanks for the reply, so how i can find the max of current the Base can drive on the collector without a saturation?

I thought that with a Vbe(sat) of 0,7 i can drive until 10mA on the collector (and 0.5mA on the base) with a gain of 20.

Base Emitter Saturation Voltage VBE (sat) V IC = 10mA, IB = 0.5mA Typical 0.70 IC = 100mA, IB = 5mA Typical 0.90

But then how i can read that: hFE IC = 2mA, VCE = 5V 200 ?

With a Vce = 5V i can push the gain until 200 ?

And so what is this information? The peek current on the collector? IC collector current - - 100 mA

Sorry for the confusion, i'm trying to bring together all the pieces. I'm reading many books, missing the pratical aspect of the thing.

You need to understand the basics of how a transistor works.

The collector current for saturation is as much a feature of the external circuit as it is of the transistor parameters.

Have a play with this:

and try changing Vcc and R1 to get a feel for how things behave.

Try also inserting a resistor in series with the emitter to ground.

Then rub those observations up against all the stuff you're reading.

A very simple model of the bipolar transistor is that it is a current controlled current sink or CCCS (for NPN, it's a source for a PNP). You put current into the base and you get hFE times the base current out of the collector.

That simple model breaks down as soon as the collector voltage gets close to the emitter voltage: a real bjt saturates, the collector voltage cannot get closer to the emitter voltage and the collector current no longer increases in proportion to base current (small signal hfe tends to zero) but in this simple model the collector current carries on increasing and pulls the collector below the emitter because a CCCS is an ideal current source whereas a bjt is not.

Here's a slightly more sophisticated version which crudely models Vbe and Vcesat:

If you look at the references in the links above you'll see that bjt models rapidly get more complex as you try to account for more detailed physical behaviour and the effects junction capacitances and electron hole transit times across junctions and through the material.

However the simple models show the underlying behaviour and for some things, are often all you need to see how a circuit behaves. It is often instructive to replace "real" models with simplified behavioural models to strip away the complexity and see underlying function.

Pity you can't buy behavioural devices Farnell or Radio Shack ...

:)