Hi All,

I am trying to rig up a comparator ciruit using LM339.I have supplied 12 to pin 3(Vcc) and pin 12(Vdd) has been grounded.Two resistors each 10k has been used as voltage devider and has been supplied to pin 5(non-inverting).

Now pin 5 has a voltage of about 6v. I tried supplying 0v and 12v to pin 4(inverting).In either of the case i got the same voltage i.e aroung .2v in the output pin 2 with respect to the ground.

I am trying build the following project.Instead of TL071, i am using LM339.
http://www.electronicsforu.com/elec...er2007/CI-05_Oct07.pdf&title=Laptop Protector

Could some one help me on this.

Nataraj

 

The 339 has open-collector outputs.
Connect a 2.7k resistor from the output pin to +12v.

Make sure that you ground all of the unused inputs.