Comparator circuit problem

What i am trying to do is change a voltage waveform which originates from a flip flop and is at 0-5V to 0-12V . To solve this i thought of using a comparator like lm339n and i created a reference voltage at about 3.5V and compared it with the one i am getting from the flip-flop exit. Problem is all seems to work fine when comparator exit is on air .If i conecct the comparator exit at another part of my circuit and i get a voltage drop at my exit which goes from 0-12v to something like 0-6v .

Plz give me an idea why this doesnt work properly , or an idea how to change the voltage from 0-5V to 0 -12V in any other way .

Hello,

Sounds like your pullup resistor is too large. Try making it smaller in value like 2.2k.