I want to make a simple 8 chanel relay multiplexer. My choice for driver IC at the moment is ULN2803A and for relays it is a 12v DC DPST relay.

I read in ULN2803A datasheet that it contains Suppression Diodes. Does this means I should not be worried about adding a diode in the return path of relay coil?


  • \$\begingroup\$ I asked a similar question. \$\endgroup\$ – Dean Apr 21 '11 at 12:16

You need to connect the common cathode (pin 10) of the ULN2803A to the positive supply of the relay, then all outputs will be protected from the counter emf produced by the relays. There is no need to add an additional diode.

  • \$\begingroup\$ Thanks, would you mind telling what type of diode should I use in this case? \$\endgroup\$ – Sean87 Apr 21 '11 at 12:00
  • \$\begingroup\$ @Sean87 - You don't need a diode, they're integrated in the IC. \$\endgroup\$ – stevenvh Apr 21 '11 at 12:51

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