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I was doing a 3*3*3 arduino cube project when this doubt struck me.
Some instructables I watched used 2N3904 transistor whereas a few used BC547.

I hava a 548 at hand and was thinking whether I could use it. I use a variety of leds - red,blue,green and yellow. So current may range between 15 to 25 mA I guess.

Can BC 548 switch in these ranges?

The terms hfe, beta, current gain, transconductance still confuse me. Guess I'm not so thorough with my basics. A little bit of googling has left me in utter confusion.

Can somebody please shed some light upon the matter?

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    \$\begingroup\$ you can directly compare them using their datasheet. \$\endgroup\$ – MaMba Nov 27 '15 at 8:22
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    \$\begingroup\$ This wiki page compares BC548 with BC547 and highlights the differences. \$\endgroup\$ – Roger Rowland Nov 27 '15 at 8:25
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    \$\begingroup\$ The main difference is that BC548 is only suitable for up to 30V, BC547 can go up to 50V - for your application it should be fine. \$\endgroup\$ – Icy Nov 27 '15 at 8:25
  • \$\begingroup\$ See my related answer here which compares a 2N3904 and a BC107. It shows the typical parameters to be looked at when comparing BJTs. \$\endgroup\$ – tcrosley Nov 27 '15 at 10:54
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You will be fine with BC548, BC547 or 2N3904 your application is not demanding.

The history of this comes from the original metal can NPN silicon devices that were called BC107, BC108 and BC109. These numbers are in ascending gain and descending breakdown voltage. According to semiconductor physics gain and breakdown voltage are interchangeable. High voltage transistors tend to have lower gain and low voltage transistors tend to have higher gain. The gain differences are not huge when comparing the 547 & 548. Early analogue circuits that had no negative feedback using the minimum number of BJTs were much more gain sensitive and ran on 9V so the BC109 with its hfe of 900 was sought after. According to folklore the manufacturer put the numbers on the transistors after they were automatically tested. Packaged transistors that didn't make the specification in one or more aspects were sold to hobbyists as F PACK's and they were big cheap bags.

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  • \$\begingroup\$ @Icy - maybe also edit the 458 to 548? \$\endgroup\$ – Andy aka Nov 27 '15 at 10:15
  • \$\begingroup\$ @andyaka - yes hadn't noticed that. Now done \$\endgroup\$ – Icy Nov 27 '15 at 10:20
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    \$\begingroup\$ This is not quite correct : gain groups were denoted by [nothing|a|b|c] after the number, with gain group c (e.g. bc109c) being the highest. The BC109 was optimised (or selected) for low noise, while others were guaranteed for higher voltages or higher currents. And this distinction remains in the 54x and 84x series. \$\endgroup\$ – user_1818839 Nov 27 '15 at 10:41
  • \$\begingroup\$ Yes the a b c did happen and the 109 was a low noise device .I had hair and was thin then . \$\endgroup\$ – Autistic Nov 27 '15 at 10:50

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