To Resist-or or not?

[SD70M]

Hi guys,

Simple question, manual3 shows driving a motor using a ULN2003A as opposed to a seperate transistor. No resistor shown.

If I was driving a relay using the ULN2003A would I need a resistor (I think I would) and if so, which value am I looking for on the relay datasheet for the equation?

Thanks
Angie

 

[nick12ab]

You would not need a resistor for a relay.

 

[SD70M]

Thanks Nick, that's put my mind at rest, hate seeing blue smoke!

Angie

 

[westaust55]

The ULN2003 and ULN2803 have inbuilt resistor within the "chip" for the Darlington transistor base.
These Darlington arrays also include a 'freewheeling' diode between the supply pin and the outputs so no further diode is necessary in parallel with the relay coil.

 

[SD70M]

Cheers WestAust, got the diode thing but didn't realise there was a resistor in there too

 

[Jakob2803]

Cheers WestAust, got the diode thing but didn't realise there was a resistor in there too

Shoulda checked the datasheet!

 

[boriz]

Resistance is futile!

 

[Jakob2803]

I just pushed a resistor across the desk. I guess that's what you call a resistance movement.