I'm building a driver for a large common-cathode 7-segment display using a shift register and BJT transistors (more details in this question).

I wanted to make it more compact by replacing the transistors for a Darlington array such as ULN2003 or ULN2803, but these only sink current and I can only figure out how to use them to drive common-anode displays.

Is there a way I can use these Darlington arrays to drive common-cathode displays? If not, are there Darlington arrays, such ULN2003 or ULN2803, that source current? If not, why not? Is it because the IC would require more transistors (as explained to me in here) and thus it would be more expensive to produce?

Should I just prefer to drive common-anode displays instead? For some reason I think there should be some simmetry in this, but apparently there's not.


1 Answer 1


Sourcing drivers are not as common as sinking drivers. I often use the UDN2981 / TD62783 as a 'high-side ULN2803'.

  • \$\begingroup\$ Could you please explain how to drive a VFD (vacuum fluorescent display) with TD62783? AFAIU, TD62783 can't sink current, so to turn off a segment/grid reliably it must be grounded through a pull-down resistor. If I use a 10k resistor a high potential is still present on the segment/grid, so I get ghosting. If I use really low resistor value, the whole thing is just sucking current constantly. Another strange thing: turning a grid on or off has no noticeable effect on a segment brightness. I have a feeling that I'm doing something completely wrong :) \$\endgroup\$
    – actual
    Commented Mar 13, 2019 at 18:36
  • \$\begingroup\$ Where did you get the idea that what you suggest is possible with that chip at all? \$\endgroup\$ Commented Mar 17, 2019 at 19:36
  • \$\begingroup\$ I bought it at a shop there it was advertized as a VFD driver, I checked the datasheet before purchasing it and found: "designed for fluorescent display applications". Probably that's some other kind of "fluorescent display applications". \$\endgroup\$
    – actual
    Commented Mar 19, 2019 at 9:06
  • \$\begingroup\$ That sounds like you are trying to multiplex? These drivers don't seem to be designed for multiplexing. \$\endgroup\$ Commented Mar 22, 2019 at 7:40
  • \$\begingroup\$ Looks like the VFD is ran out of its filament/phosphor resource: the display is very dim, there is no enough contrast between active and inactive segments, so that's not ghosting. Have tried to drive it directly by hands from the lab supply, still no contrast even with the proper voltages recommended to achieve the highest contrast possible (1.5V/100mA on filament, 24V for active grids/segments, -4V for inactive grids). Searching for a compatible VFD now. Thanks for the moral support! :) \$\endgroup\$
    – actual
    Commented Mar 24, 2019 at 14:39

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