I've been trying to read up on BJT transistors to figure out how I can use one for a simple switching application. In order to calculate the resistances I need, I need to figure out VCE, the collector emitter saturation voltage and VBE, the base emitter voltages. But I'm noticing some of these data sheets seem to have conflicting data the way I am interpreting them.

For example, in this P2N2222A NPN transistor, I can look in the "ON CHARACTERISTICS" table and see that VCE has a max of .3V for IB=15mA and IC=150mA.

However, in Figure 4 there is a graph of IB vs VCE. If I look at the plot for IC=150mA, and then go to IB=15mA, I see VCE=.1V and not .3V. Collector Emitter Voltage Graph

Is the datasheet just telling me that at a maximum, the graph will be shifted up so that the value is .3V at IB=15mA? And if so should I expect the general shape of the graph to still hold?


1 Answer 1


What you are seeing is the difference between guaranteed maximum and typical. Typical specs are mostly marketing BS. What you need to design to are the min/max specs.

The curves show typical values, so you can't rely on them. Their point is to give you some idea how the part behaves, even if you have to use different numbers to determine part values in your design. Think of the curves as kindof interesting, but not much more.


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