Questions about the IC ULN2003?

In
**broken link removed**
I read: (….. It contains seven open collector Darlington pairs with common emitters.) What does he mean by saying common emitter? Is he mean all emitters of the 7 Darlington pairs are all connected together and with the common ground (pin #8)?


How to use pin #9?

What the difference between driving a 12V relay using this IC or using a simple suitable transistor?

Thank you very much.

Hi,

Gosh, not an easy datasheet to comprehend if you are not familiar with that kind of IC - neither the one you linked to nor the one I just read.

If you want, have a read of this other datasheet in the link, it may help to answer your questions:

https://www.ti.com/lit/ds/symlink/uln2003a.pdf

When you compare the IC pinout picture to the table on page 3, doesn't it look like the pin table has a mistake there regarding pins 7, 8 and 9? :O

Common emitter means emitter connected to ground, as each in/out is the same on this IC, they are all connected to the same point, but that isn't what common emitter means (search online for common base, common collector and common emitter, useful to know difference); in this datasheet it says typically connected to ground through pin ...7? NO! pin 8. So then pin 8 is IC and the common emitters ground, I think.......

Page 14 shows a "typical application" and pin 9 ("COM") connected "to V Supply".

A difference could be how many things do you want to solder (pin count)? 1 transistor, + flyback diode, + any required resistors (maybe 11 points + the relay connections) or 16 solder points + decoupling capacitors + the relay connections? For 1 relay I see little point in using an IC with 7 outputs if only one is needed.

samy555 said:

What does he mean by saying common emitter? Is he mean all emitters of the 7 Darlington pairs are all connected together and with the common ground (pin #8)?

Click to expand...

Exactly.

samy555 said:

How to use pin #9?

Click to expand...

For inductive loads, such as the coil of a relay, could act as a protective device that provide a closed path to suppress spikes generated due to commutation. It is usually called as free-wheeling diode.

samy555 said:

What the difference between driving a 12V relay using this IC or using a simple suitable transistor?

Click to expand...

Space saving at the PCB.
This part is particularly suited for driving arrays of 7-segment displays, but you can use elsewhere.