ВЭФ 12 (Astrad VEF 12 Project) - including a transistor tutorial

[Mark Hennessy]

"If we know the voltage across a resistor, and we know the value of that resistor, what do we also know?"

Clearly, current values can be found.

Right! That's all I needed. So forgive me if I ignore the rest of your post for the time being

So we have 1V across a 1k resistor. Now, I'm pretty poor at maths, but 1V divided by 1k must be 1mA.

Let's move on.

Here's an equation that you might have seen before:

IE = IC + IB

In words, the emitter current is the sum of the collector current and the base current. This is just Kirchhoff's current law, which I'm sure you've met already.

Now, what about IB? We've not considered this yet, and frankly, I'd rather not bother. It's not quite zero, but it's insignificant. From a look at the datasheet Lawrence posted earlier, we can see that it'll be somewhere between 0.5% and 0.125% of the collector current. Given that we're dealing with real-world components and measurements, we can safely ignore that today.

So, IC equals IE

Therefore, everything we have done so far has been to set the collector current to 1mA.

The final step of the journey is to determine the collector voltage.

This again is just the application of Ohm's law. But, because I'm very fair, I'll mention that there is a trap that folk usually fall into at this stage. Only a small one, but useful from the learning point of view, so don't feel bad if it happens... So I'll say no more at this point - over to you: what is the collector voltage?