bc 547 and bc 548?

Question

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?

Answer 1

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 h_fe 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.