Hello,I am needing to drive four transistors (NPN, NTE123, 2N2222, etc), which arebeing used as switches for fairly equivalent loads, from the output of a4013 flip-flop.Is there any reason not to just use one base resistor for all fourtransistors, or am I missing something really obvious?Thanks for any insight into this,Jon

In the absence of emitter degeneration resistors, yes, you are missing something obvious.Your Vbe will vary from one transistor to the next; with one base resistor you will find that one transistor tends to 'steal' the current from the bases of the other three transistors.With four diodes the one stealing the current would get hot, reducing its voltage drop and making it steal even more current. With transistors that are supposed to saturate the effect would be more complex and less predictable (a half-on transistor will get hotter than a fully on transistor, but one that never really turns on won't get hot at all).Just use four base resistors. It'll make your life easier in the end.-- Tim WescottWescott Design ServicesPosting from Google? See "Applied Control Theory for Embedded Systems" came out in April.See details at

Can I use one base resistor for several transistors?

Dec 01, 2006 21 Replies

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Jon Danniken 19 years ago

Oh, for sure; the digi-key interface makes it a lot quicker to find exactly what you're looking for.

Jon

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Jon Danniken 19 years ago

I wish I could say the same. I made *one* order with Newark a few months ago, all items listed as "in stock". After two days, I didn't hear anything back.. Emailed customer service, still no response for three days afterwards.

Finally called them on the phone to find out that several items were not in stock, and wouldn't be for several weeks.

I cancelled the order right then and there. I still continue to get spammed by them at least once a week.

I'll never do any business with Newark again.

Jon

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