Author Topic: darlington transistor is not functioning  (Read 11272 times)

george1

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darlington transistor is not functioning
« on: August 01, 2003, 09:06:38 AM »
hi,
  I have a 24 volt dc motor with a  5 volt encoder.  i supplied 5 volts to the encoder through the analog 5volts supply .  I get a 5 volt pulse, then I hook it up to a darlington transistor ULN2003 as it was described in the manual.  Now I only get .649 volts.  Is there I skipped over in the manual  in the manual that was left out?  
I tried several transistors and the same results.  So I assume I hooked it up wrong
« Last Edit: December 31, 1969, 04:00:00 PM by 1076562000 »

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Re: darlington transistor is not functioning
« Reply #1 on: August 01, 2003, 07:29:38 PM »
From your description, the darlington transistor array you used is actually working perfectly!!

When you supply 0V to ULN2003A input, the corresponding output is turned OFF (i.e. open circuit).

When you supply 5V to the ULN2003A input, the corresponding output is turned ON and the purpose is to conduct the current to ground (0V). However, there is always a voltage drop of about 0.7 to 0.8V so it is not a perfect switch unlike  relay contact but it will still serve the purpose of sinking current from the load.

Hence, when you connect the output of the ULN2003A to the input #3 and #4 of the PLC, it will turn ON the PLC input when the voltage is 0.7V and turned OFF the PLC input when open circuit.
« Last Edit: December 31, 1969, 04:00:08 PM by -1 »
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