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I have a table that presents DC Current Gain for BC548B transistor:

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and a graph that presents Normalized DC Current Gain:

enter image description here

Are those two things related? What does "normalized" mean? Why is the Y-axis labeled with numbers from 0.2 to 2 instead of something around 110 to 450?

My reason for asking this question is that I need to know the DC Current Gain for this transistor at Ic=2.0mA and Vce=5V, and whether it would be significantly different at Ic=2.0mA and Vce=0.5V-1.2V.

The table and the graph come from the datasheet for an On Semiconductor BC54X transistor: http://www.onsemi.com/pub_link/Collateral/BC546-D.PDF

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1 Answer 1

up vote 6 down vote accepted

"Normalised" means "relative to some specified reference value".

In this case the Y axis = 1 when Ic = ~~ 7 mA. This means that somewhere else they will have specified the gain AT 7 mA. This graph allows you see see how the gain varies realative to the gain at 7 mA as Ic is varied.

At 0.1 mA and at 100 MA the Y axis value is 0.5 so we know that the gain is 0.5 x the value at 7 mA.

Why they chose 7 mA as their reference point I know not.

They could have just used actual gain BUT this tells you how a tyical device behaves, regardless of the actual gains, which can vary between devices.

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This curve is for the BC546 (Figure 3). The curve for the BC548 (Figure 1) is normalized to 5mA and the gain at 2mA is 0.9. Why they chose different currents for the two devices only OnSemi knows. And I must learn to type faster ;) –  MikeJ-UK Mar 9 '12 at 22:38
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