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Need help in using Darlington Pair IC ULN2003A


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Hello Guys,

I need some help in using ULN2003A Darlington Pair Array IC in my project, let me explain little about my project.

I want ULN2003A IC to drive 6VDC Relays, and my logic inputs are CMOS, here the input for ULN ic is coming from BCD-7 Segment IC 4511, and the output of ULN2003 is connected with 7 Relays, The relay's Normally Open Contact is used to drive 200V Circuitry.

Please help me what is going wrong..........

Any new idea will be helpfull for me.

Thanks

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Please help me what is going wrong..........

You forgot to say what is going wrong.
You forgot to attach a schematic of how they are connected together.
You forgot to say the current drain or resistance of the relay coils, and the power supply's current capability.
Did you forget to connect the ULN2003A COM pin 9 to the relays' +6V supply?
Did you forget to use a nice big supply bypass capacitor?
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Perhaps I can help out, I have used 2203s and relays in a similar way and they worked well.

The 4511 has its outputs active High (voltage level is close to the positive Vdd) when segments are turned on. Each one of the 7 transistors inside the 2003 work as an open-collector inverter, which means that the output connects to Gnd when the input is driven High. So the 4511 can drive the 2003 directly, and the relays should be connected between each one of the 2003 output and some positive supply voltage.

The 2003 pin 9 is the common emitter returns for the transistors, this should be connected to the ground, (same as pin 8 on the 4511) Pin 10 on the 2003 is the common for all the protective diodes, this should be connected to the same supply as the relays.  This supply for the relays should preferrably be separate from the 5V supply for the 4511 and its friends, so that the noise from the relays turning on and off do not affect the logic circuits there. Besides, 5V is a little too low for turning 6V relays reliably on.

If the 5V power supply for the rest of the circuit is taken from a regulator, maybe the relays can be powered from the supply voltage appearing before that, or a separate 6V to 7.5V supply could be obtained using another regulator circuit.

To test this, hook up the 2003s to the relays and the power and ground but not to the 4511 (or pull the 4511 out of its socket if possible, that will make this easy), and put 5V (from pin 16 on the 4511) on each of the inputs, to cause the 2003 to turn the corresponding relay on. Unconnected 2003 inputs will behave as Low with the transistors Off, since there are pull-down resistors inside the 2003.

Ashtead

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Perhaps I can help out, I have used 2203s and relays in a similar way and they worked well.

The 2003 pin 9 is the common emitter returns for the transistors, this should be connected to the ground, (same as pin 8 on the 4511) Pin 10 on the 2003 is the common for all the protective diodes, this should be connected to the same supply as the relays.

Hi Ashtead,
I couldn't find a datasheet for an old ULN2003, but the new ULN2003A has pin 9 different from your description.

post-1706-14279142605398_thumb.png

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Oops! Sorry for the mis-information, I was wrong about the pin numbers: The correct ones would be Pin 8 Ground (or common emitter) and Pin 9 where the diodes go, for the 16-pin 7-channel parts.

Pins 9 and 10 would have been right for the 2803 with 18 pins and 8 drivers in it...

I don't think there are any variant pin-outs on these, my older 2203s and the more recent 2003s all are the same.

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