What's the difference between BC547/BC547A/BC547B/BC547C?

[sonic]

Hi!
I'm trying to control a flash with a headphone out using this circuit:

I hope the 2k2 resistors that I already have will also work.
After ordering 50 BC547Cs, it occured to me that there are 4 varieties with different h_FE:

Variety	Min	Max
547	110	800
547A	110	220
547B	200	450
547C	420	800

What's behind this?
How can the variety BC547 span the range of all the others?
Does all that matter for this circuit?

[Simon]

just make sure the resistors are the right value to acount for the lowest gain you may have.

the letters after the part numbers can often mean different CE voltages

[kayvee]

The 547 is the non-graded version, whereas the A, B and C versions have been graded into specific hfe ranges.

[sonic]

VCE	= 4.8 V
IC	= 1.6 mA

[SeanB]

Basically any of them will work there. The ungraded one is just tested on the line ( hopefully) and is not graded, or is the selection that is out of either the top or bottom gain selections so may work perfectly or not at all. This is often the case that the cheapest components like transistors are not tested fully during manufacture, just are done on a sample basis. The A,B,C ones have had a simple gain test during production and are binned into the 3 grades as they test out. Often the cheapest is not the lowest gain but typically the mid, where the processing places most of the devices.

The reason why you might want a gain group is that some circuits need a gain in a certain range to operate correctly, and ones with too high or too low a gain may not operate properly over the full operating condition range, or may saturate near full signal level.