hi , i am trying to connect output of DAC0808 i.e its 4th pin to LM324 ,i want to get output of LM324 to be negative . now when i give positive voltage at Vref(+) i.e pin 14 of DAC of dac i get a positive voltage at output of LM324 ,but when i give negative voltage on this same pin i get zero output of LM324.
similarly when i give negative voltage at Vref(-) i.e pin 15 i get positive output of LM324 and gving a positive voltage at same pin gives zero output.please help
in proteus it is runing the proper way i want but i am facing this issue in hardware.proteus file is attatched

 

its urgent friends please guide me

 

Eight minutes and your crying for a reply? Give it some time, man. The people on here are providing help FOR FREE.

 

Eight minutes and your crying for a reply? Give it some time, man. The people on here are providing help FOR FREE.

ppl here always helped me , n m nt crying i jst asked 4 urgent help cux i hv 2 complete things in a few hours time

 

What voltages are the power supply pins on your DAC and your LM324 connected to?

 

DAC is given 10v at refrence n DAC power suply pins r coected to 5v n ground n LM324 is connected to +15v n -15v

 

If the DAC is powered by 5V and ground, and the output is going to a node that is being held at virtual ground, how is the DAC expected to draw current from that node? Where is that current supposed to go?

 

ppl here always helped me , n m nt crying i jst asked 4 urgent help cux i hv 2 complete things in a few hours time

This isn't Twitter. Please use complete sentences and not cute texting shorthand.

And posting a follow-up because you haven't received a replay after just 8-minutes is quite unreasonable. Don't be surprised if it sometimes takes a couple of days (or longer) for it to catch the attention of someone that cares enough to respond.

 

You can't make the DAC0808 source current, but you can add an offsetting current (through R1), so that the op amp output will swing positive and negative.
The DAC output sinks 0 to 2mA, controlled by the digital inputs. R1 sources 1mA. The result is that ±1mA flows through R3, for ±10V at the output.
Note that the output will be at zero when the input code is 80 hex (128 decimal or 10000000 binary).
Note also that you MUST have a negative supply for Vee on the DAC.