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I intend on driving 24VDC relays with darlington arrays of the ULN200X series. Since the darlingtons will be driven by a 3.3VDC outputs I am hesitating on whether I should choose ULN2003 or ULN2001.

As mentioned in the datasheet ULN2001 works with: general purpose, DTL, TTL, PMOS, CMOS. However it does not mention the voltage levels. On the other hand ULN2003 works with 5V TTL, CMOS. The only difference between the two would be a series resistor:

enter image description here

Since the resistor is not existent in the ULN2001, would this mean that driving it with 3.3VDC would be much easier than in the ULN2003 case?

Each relay draws ~20mA. According to the electrical characteristics, "VI(ON)" of max 2.4V is sufficient for 200mA loads, in the case of ULN2003. I guess this means that ULN2003 should be ok with 3.3VDC but I still wanna make the better choice between the two.

The MCU I use is stm32 with general purpose I/Os which are TTL and CMOS compliant according to the datasheet.

Advise on alternative components regarding this application is most welcome.

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    \$\begingroup\$ A BJT used as a switch always needs a resistor in series with the base. Always. The ULN2001 needs that resistor to be external, while the 2003 has it internal. \$\endgroup\$ – Hearth Jun 9 at 13:09
  • \$\begingroup\$ @Hearth Well it makes a lot more sense now that you have mentioned it :D. Thanks. \$\endgroup\$ – Phill Donn Jun 9 at 13:24
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    \$\begingroup\$ ULN2001A Status: Obsolete \$\endgroup\$ – Tony Stewart EE75 Jun 9 at 13:51
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The ULN2003A is better because 3V drive voltage is high enough and they are infinitely more available than ULN2001. It also saves the external resistors or network(s) that you would otherwise have to provide.

Perhaps confusingly, there are a couple of Chinese makers (Mixic, HGsemi) who have a 'ULN2001' which is similar to a ULN2003A but with only three channels and an additional 4K pull-down resistor, in an 8-pin package.

If memory serves, the ULN200x series was originally made by Sprague Semiconductor, which was sold off to Sanken of Japan about 30 years ago. Some models (ULN2003A/ULN2803A) became popular and were copied by a by a number of other companies.

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The uln2003 would be the choice. For advice on other devices, I’d advise that other options might be the likes of the TPIC6B595 if you want to save port pins, component count and space. You’ll need some level translation as it needs 5V logic levels.

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