The Questions about STC12C5A60S2 Drive Relay

[ling1995]

Hello,all.Thank you for taking time to read my post.

I would like to ask a question about STC12C5A60S2 drive relay--5V by using uln2003.

My schematic diagram is given below.I have add the pull-up resistance and the wiring are no problems. But I really don’t know why can’t relay pick up?
Can anyone help me ? Thank you a million.

 

[gar]

170515-0820 EDT

ling1995:

I don't know either. I can't read the fine detail in your diagram. I hope the relay supply voltage is +12 and not -12.

I have never worked with a ULN 2003, but looking at the datasheet it is good for a 500 mA relay load and outputs can be paralleled for higher current, and internal reversed biased diodes are included.

If you short the ULN 2003 output to common does the relay change state? If so, then without the short what voltages do you read between the ULN output pin and common when you change the input to the ULN? This should swing almost the full supply voltage to the relay.

If you do not get the expected output swing, then what is the change in voltage at the input to the ULN? If we assume a beta over 500 or so, then a 5 V input change should give you a 500 mA output change. Make sure the ULN channel has not been damaged.

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