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problem ............uln2804 to drive a relay 12v...

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sherazi

sherazi

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i have connected one terminal of relay to fix 12v and the other to uln... the question is would it work if i supply logic 1 to the uln...

i assume that when i would supply logic 1 it would turn the relay on... the connections are same as in pic except instesd of 24vdc i m using 12vdc...

but it doesnt work.. what could be the prblem?



also i have tried to check it on breadboard... connecting in the same fashion and appliying both ground and 5v to the pin 1turn by turn.... nothing happens............
 

The pin numbers are incorrect for ULN2804, that has 8 channels and a 18 pin package. They are right for ULN 200x.

By specification, ULN2804 is intended for 6 to 15 V CMO logic input, while ULN2803 is the correct choice for 5V logic. But 2804 can
work with a light load and 5V logic input anyway.
 

Hai,
Your statement says ULN2804 but your circuit is ULN2003.
you are sinking the current through load. So, No problem in supply voltage. Make sure the relay current should be less than the ULN datasheet other wise shunt the pins.
First Check the condition of the relay, by simply shorting 16 and 8 th pins in your circuit. If it is fine then change the IC.

Refer the circuit for ULN2804 attached here with.
 

just replaced the two ics didnt help as both were damaged.... the third change made the circuit working
 

The Vcc supply to the ULN chip should be connected strongly. Through which freewheeling diode is connected internally. The relay common voltage and the vcc supply for ULN should be in same potential.
 

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