ULN2003A Revisted

[Steve_88]

I would like to replace my transistor driven relays with the latest and greatest relay driver.
A UNL2003A etc. I would also like to use a shift register or I/O expander to reduce the number of I/O required to control the relays.

The Relays are 12 VDC with 160 ohm coli resistance (75ma).

I will not need more than three relays activated at any given time.

Questions:

Should I use external diodes to clamp the spike from the relays?

Is the ULN2003A a good fit?

Any suggestions for an 8 bit shift register etc? I would like to be able to turn one relay on, then turn another on at another time and not have the first relay drop out while it switches...Not quit sure how to say that.......

Concerning the hook up, I assume I would wire 12 volts directly to the relay, with the other side of the coil connected to the out of the ULN2003 which when active will complete the ground path and the relay turns on?

Thanks very much,
Steve

[Dave]

Steve_88 , Try one of these... I use them all of the time.... UCN5841A

Dave Purola,
N8NTA

[Steve_88]

Hi Dave,

Thanks that looks perfect. Though using www.findchips.com does not reveal where I could get a couple? No luke at Digikey etc......

If you have extra's? Want to swap for something....lol

-Steve

[paul borgmeier]

Steve,

Check these out

http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=2556324;keywords=5841

[Dave]

Steve_88, I had forgot to mention that Allegro changed the part number. The attached website has all of the info and samples available. The new part number is A6841.

http://www.allegromicro.com/en/Products/Part_Numbers/6841/index.asp

Dave Purola,
N8NTA

[Steve_88]

Thanks everyone, I'll try a few out, I'm sure they are perfect.

I'll be re-desinging a circuit board to use these chips, should I add external diodes?

Thanks,
Steve

[Dave]

Steve_88, If you like, Just make sure you tie the common cathode line on the driver to the supply you are using for the relays and not 5 volts.......

Dave Purola,
N8NTA