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[SOLVED] {LM331} Voltage to Frequency Convertor 0-10V to 0-50Hz(24Vpp)

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dhruv_electro

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I have tried following circuit to convert my 0-10V DC analog voltage to 0-50Hz (24Vpp) using LM331. But I don’t get the desired output. When I try to build the same circuit on breadboard it gives 24V output on the PIN3 for all the range of 0-10V.

1.png

  1. Is this IC capable of converting my 0-10V into 0-50Hz(24Vpp)?
  2. My requirement is NPN output. Is it possible with this IC?
  3. If both of the answer is Yes, Is there anything I am doing wrong?

All the capacitors are ceramic disk capacitors.
All the resistors are MFRs.
 

I have some help from other forum and done some self correction and I got the pulse output. As I have broken my oscilloscope I can not check output, I just inserted LED

1.png

Now my question is:
  1. Is there any problem in this circuit that I should consider?
  2. What duty cycle will I get? will it be 50%?
  3. Is it 24Vpp NPN output?
 

I suggest you to look carefully into the RC input at pin 5. There may be additional problems.
 

Try and follow the reference manual from manufacturers of the chip.
For your experiment Reduce the Vs to 15v. Also, for full scale -10v is required at the input and not +10v. Some capacitors value can be change check the datasheet.
 

ahmed-agt said:
Try and follow the reference manual from manufacturers of the chip.
For your experiment Reduce the Vs to 15v. Also, for full scale -10v is required at the input and not +10v. Some capacitors value can be change check the datasheet.
Click to expand...

I think you are referring to the page 14 figure 16 of https://www.ti.com/lit/ds/symlink/lm331.pdf

But this is different specification than my application. I think according to LM331 datasheet, this IC is capable of having Vs=24V and Full scale 10V input. If you think otherwise can you point out in datasheet where it mentioned?
 

Hi,

are you familiar wth microcontrollers?
If yes, then use the ADC and read the input voltage and generate the desired frequency.

Simple task. Needs less parts than your solution. Just some program.


Klaus
 

c_mitra said:
I do not see a resistor connected to pin 5. You can follow some of the example diagrams given in the datasheet.
Click to expand...

I have connected R2 at Pin 5 (which is Rt as mentioned in datasheet).

KlausST said:
Hi,

are you familiar wth microcontrollers?
If yes, then use the ADC and read the input voltage and generate the desired frequency.

Simple task. Needs less parts than your solution. Just some program.


Klaus
Click to expand...

Yes I am familiar with Microcontroller world. But in that case we required :

  1. Power Supply
  2. Output of the MCU needs to be driven using Transistor for 24Vpp NPN.

With this LM331 both will be served.
 

dhruv_electro said:
I have tried following circuit to convert my 0-10V DC analog voltage to 0-50Hz (24Vpp) using LM331. But I don’t get the desired output. When I try to build the same circuit on breadboard it gives 24V output on the PIN3 for all the range of 0-10V.

View attachment 130669
.
Click to expand...

This is one of those old analog ICs which are very straightforward to use, it just works, if one adheres to the simple guidelines outlined in the datasheet.
Over the decades, I've built many applications using the LM331 and have never experienced trouble with the circuit itself.

The problems I've experienced have always been related to errors in wiring and/or components, solder defects, or in the case I built one on a protoboard, a spring contact below was intermittent.

There is another problem that was very rare in the late 1970s but nowadays is prevalent: counterfeit devices.
Thus, the only advice I can give you is: check everything. Again.
In my instance where the defective protoboard was at fault, I found it by measuring continuity with a DMM from an IC terminal to a capacitor terminal.
 

schmitt trigger said:
Over the decades, I've built many applications using the LM331 and have never experienced trouble with the circuit itself.
Click to expand...

Can you comment on this?

dhruv_electro said:
View attachment 130681

Now my question is:
  1. Is there any problem in this circuit that I should consider?
  2. What duty cycle will I get? will it be 50%?
  3. Is it 24Vpp NPN output?
Click to expand...

I think circuit is working, as I have checked with LED, but now problem is related to linearity. Unfortunately I have broken my CRO. I just request you to comment on the circuit I have modified.
 

dhruv_electro said:
Can you comment on this?

The LM331 is a very robust circuit that has been sold by the tens of millions for over 45 years: it works. You have to follow some basic guidelines, but it will reliably work.

I think circuit is working, as I have checked with LED, but now problem is related to linearity. Unfortunately I have broken my CRO. I just request you to comment on the circuit I have modified.
Click to expand...
The circuit looks ok.
If your scope is broken, How can you check V/F linearity if you don't have an instrument to check frequency?
There are many multimeters which include a frequency function.....can you borrow one?
 

schmitt trigger said:
The circuit looks ok.
If your scope is broken, How can you check V/F linearity if you don't have an instrument to check frequency?
There are many multimeters which include a frequency function.....can you borrow one?
Click to expand...

Yes I have ordered new Fluke 17B+, Once I receive it, I will check the results.
 

dhruv_electro said:
Can you comment on this?



I think circuit is working, as I have checked with LED, but now problem is related to linearity. Unfortunately I have broken my CRO. I just request you to comment on the circuit I have modified.
Click to expand...


Are you sure you circuit is working now? I guess there is some issue could be there at Current Output & Threshold Input pins. Check for the connections properly. Because I suspect some small mismatch is there
 

hobbyckts said:
I guess there is some issue could be there at Current Output & Threshold Input pins.
Click to expand...

Is there anything wrong with RL(R3) and CL(C3)?

Actually when I change Voltage Feed in Rin(R1) from 0-10V, LED blinking rate is changing. I at least confirm this for visible range i.e. lower range up to 1.5V(15Hz). For Voltage greater then 1.5V, LED blinking rate is not visible.
 

I had quickly checked it, and the circuit is similar to figure 14 in the datasheet, without the optional offset components.

I did not check the component values, though. The OP should easily be able to calculate those.
 

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