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enter image description here

Assume that I have VCE = 10Vdc, IC = 1mA. How can I find out hfe in Figure 11. There are 4 curves; what curves that we need to read?

Reference from: https://www.onsemi.com/pdf/datasheet/2n4401-d.pdf

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2 Answers 2

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Only pay attention to the curves that are marked, the others are there because someone copied an older datasheet. They refer to the 2N4400 part.

enter image description here

They represent some kind of expectation of the behavior, however you should primarily work with the guaranteed numbers in the datasheet. The curves provide a way to get some confidence of the behavior if your conditions are not exactly where the performance is guaranteed.

For example, the numbers on the above-linked datasheet guarantee a minimum gain of 40 for the 2N4401 at 1mA and 1V Vce. The curves seem rather more optimistic. As a designer you should be pessimistic if you want things to always work.

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    \$\begingroup\$ +1- Curves are for qualitative understanding of behavior, datasheet min/max numbers are for designing! And datasheet typical numbers are often useless..... \$\endgroup\$
    – John D
    Commented May 9, 2023 at 20:20
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As far as I can see, only 2 of the curves are useful because there's no explanation in your (unattributed) figures as to what the other two curves represent.

The hfe is shown for a high and low gain unit, so you could expect the typical unit to fall somewhere in between these two curves. At 1 mA and 25 C with 10 V Vce that would be between about 140 and 200. We don't know if these two units are the min and max possible, so you COULD potentially see units outside those values.

The datasheet shows a min hfe of 40 at 1 mA Ic and 1 V Vce, so it's possible that the second set of curves are for 1 V Vce. (Though I think Spehro has the right answer on the extra curves.)

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  • \$\begingroup\$ (Same graphs appear in Fairchild's datasheet. My best guess for the unlabelled curves is @1 V, same units/specimen.) \$\endgroup\$
    – greybeard
    Commented May 9, 2023 at 20:13
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    \$\begingroup\$ @greybeard I was just editing my answer to say the same thing, though I think Spehro has the right answer. \$\endgroup\$
    – John D
    Commented May 9, 2023 at 20:16
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    \$\begingroup\$ +1 I know this only because I've run into it before. Whoever goofed this up as an intern has probably retired by now. \$\endgroup\$ Commented May 9, 2023 at 20:28
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    \$\begingroup\$ @SpehroPefhany It wasn't me, LOL :) \$\endgroup\$
    – John D
    Commented May 9, 2023 at 20:30

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