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Voltage to Frequency conversion problems LM331 ON PROTEUS

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caiolips

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Dear Friends,

I need Help with an VFC LM331!

I tried to folowwing the circuit of national semiconductor (VFC NATIONAL SEMICONDUCTOR.png) on PROTEUS (VFC SIMULATION.png). With a quite diferent parameters (VCC = 5V), and i couldnt reach the equation of circuit). The frequency in simulation is so high, even the PIN2 conected to the ground, the output frequency is about 60KHZ with 1V INPUT. By the equation of this VFC, the PIN2 conected to the ground, the output frequency should be ZERO. I remove 12k resistance, because with this value, i cannot simulate. I saw a guy with the same problem in this forum, but without solution.

How i can solve this problem???
 

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  • VFC NATIONAL SEMICONDUCTOR.png
    VFC NATIONAL SEMICONDUCTOR.png
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  • VFC SIMULATION.png
    VFC SIMULATION.png
    132.3 KB · Views: 544

You say to substitute the ground to a source with this voltage (2V)?
 

Yes, because if you short the pin 2 to ground I think the reference of this circuit won't be valid. I have no idea why you can't simulate with the original resistors, describe more about it why you can't.
And on your schematic the Ct is 100nF, on the right figure it is 10nF only. I don't think it is the cause of high frequency, I just mention it to you.
 

I adjusted all parameters and the problem remais....

Why i can do? :(

circuitproblem.png
 

How much is the input voltage? How much is R4? How much is the supply voltage?
 

INPUT VOLTAGE : 1V
R4: 10k
SUPPLY VOLTAGE: 15V
 

This certainly does not answer the above question, but at occasions when I'm not sure about if one component model is properly working in a specific simulation environment and have no other similar option, I usually do the same experiments on another simulator just to check whether the error is at the circuit or at the component model itself. In that case, a candidate for Proteus would be LTSpice (freeware tool), and a model for LM331 can be found in this thread here (ok, another forum, but belongs to the same media group from Edaboard).
 

I would suggest to try it in an other simulator either, and with an other model too, if it is possible.
And I would run simple transient analysis instead of real-time oscilloscope simulation first.
 

There seems to be some error with the proteus model regarding the one-shot section in the model. The problem is present in both the LM231 and LM331 models.
 

Someone can help? i need to do this in proteus :(
 

Ok, i gave up to adjust my project, but i want to try adjust for real model. For this, i want to divide the output frequency by 50 times, how i can do this? You guys know a component or a math function on proteus that do this easily?
 

caiolips said:
Ok, i gave up to adjust my project, but i want to try adjust for real model. For this, i want to divide the output frequency by 50 times, how i can do this? You guys know a component or a math function on proteus that do this easily?
Click to expand...

Make a synchronous counter modulo-50 with flip-flops.
 

Hi,

Look for frequency divider type ICs that have a model in Proteus.
 

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