proteus dac

[liewchin]

hi someone who is experts in proteus can help ?
I have set my power in configure power rails which are , Vcc =15V, VEE=-15V, Vref=5V
The schematic diagram would be something similar shown as below. i don't know what wrong ,why I get a 13.5 V at full scale . please help me ,I'm a beginner of using proteus .

 

[KlausST]

Hi,

What value do you expect?

Did you use voltmeters in your simulation to trace the signal from beginning to end?

Klaus

 

[liewchin]

Hi,

What value do you expect?

Did you use voltmeters in your simulation to trace the signal from beginning to end?

Klaus

Hi klaus , i expect to get a value of 4.99V when the input number is 11111111.
yes , I'm using a dc voltmeter

 

[KlausST]

Hi,

You have a simulation tool, so use it to debug your circuit:
* what is I14?
* what is Iout?
Of the DAC.

Klaus

 

[liewchin]

Hi,

You have a simulation tool, so use it to debug your circuit:
* what is I14?
* what is Iout?
Of the DAC.

Klaus

hi , i got 4mA at I14 but it supposed be 1mA

and the iout is 1.35e-7 also not same with the calculation

 

[KlausST]

Hi,

I doubt that "Iout - of the DAC" is that close to zero.

I14: just go on debugging straight forward. The current should be determined by R1. So what are the voltages at both sides of R1 wrtg?

Klaus

 

[liewchin]

Hi,

I doubt that "Iout - of the DAC" is that close to zero.

I14: just go on debugging straight forward. The current should be determined by R1. So what are the voltages at both sides of R1 wrtg?

Klaus

not sure , but is it this what you mean ?

 

[liewchin]

View attachment 175243
not sure , but is it this what you mean ?

Hi klaus,

i just realised i will get the same answer with theoretical calculation if I divide by 2 . but I dunnoe why divide by two .Thanks in advanced

 

[KlausST]

Hi,

When thereis +5V at one pin and -5V at the other pin, then it's 10V in total across the resistor.
Divided by 5kOhms this gives 2mA.

I can't see why there is -5V at Pin 14.

--> a guess a simulation (library) error.
But I didn't go deep into the datasheet.

Do you have a real circuit to verify against?

Klaus