# Transistor array with a common base

I'm looking for a transistor array IC with a common base to all the transistors, but I'm having some trouble finding what I'm looking for. Essentially, what I want is to take 8 data lines in parallel and be able to (somewhat rapidly) switch them on and off - that is, for 8 lines, switch all of them on and all of them off with one input line. I can do this with 8 individual transistors, splitting the input line itself into 8 parallel bases, but I'm hoping some actual EE out there - i.e., not a dabbler like me - knows of a nice little chip that will do the trick and save me some soldering.

You can imagine what it's like trying to search for "transistor integrated circuit", but that's what I want - an IC with 8 NPN transistors, all of which take their base off of one pin.

MORE DETAIL:

I'm attempting to drive quite a few 14 segment dual digit LED displays (like this one - the internal circuit diagram is important to this issue) with a fancy little LED display driver here (details less important. Fancy 16 bit shift register.) The LED driver has some nice features that would be annoying to duplicate, like individually-controllable PWM dimming for each segment, and this would be just fine with a seven segment LCD without multiplexing. Shift in the bits, latch it up, and we're good.

Unfortunately, the 14 segment LCD's only seem to work through multiplexing, as you have 8 input pins that are multiplexed among 4 different "regions" by choosing the anode. You can't just latch the bits you want on the driver and forget it - you need to control the bits as a combination of anodes and cathodes.

What I'm thinking of now is to drive a closed loop shift register with e.g. 0001 in a loop and choose the 8 cathode inputs by and-ing or switching them 8 at a time out of 32 latched input lines (that is, 2 of the driver chips, but only 8 bits of those chips at any one time). This way I would be able to shift the desired bits into the registers and ignore the whole circuit from the microprocessor's point of view (minus the shift merry-go-round clock pulse, which is minor). Just let it round-robin multiplex itself until I want to come back and display something else.

How about using a 74HC240 or 74HC244 tri-state buffer IC and use the OE input to switch multiple outputs?

• Yes, this is exactly the sort of thing I was looking for. Thanks! – Matt Mar 22 '12 at 18:59

If you can find a source for these ICs:

• M54513P is a plain 8 x 50mA NPN transistor array.
• TLC59213 is a more sophisticated choice for your application. All 8 outputs (current source, 500mA each) are latched and controlled by a common ~CLR input for shutdown.
• Those are common emitter arrays, not common base. – stevenvh Mar 22 '12 at 10:20
• The M54513P is an 18 pin DIP IC and all 8 input pins are on one side: pins 1-8. Connecting their pads would suffice the requirement: "what I want - an IC with 8 NPN transistors, all of which take their base off of one pin", I suppose? My understanding is that @Matt wants to avoid the trouble of soldering 8 discrete transistors. As far as I know, there are no generic common base transistor arrays. See nteinc.com/linear_web/array.php?a=12 as NTE (formerly ECG) is a benchmark for generic parts and replacements. – shimofuri Mar 22 '12 at 10:50