Hi Team,
Our customer is looking for an alternative to LM566 and would like to know if he can use the LM331 voltage to frequency converter.
According to our customer, in LM566 when the control voltage increases, the output frequency decreases. While in LM331 when the control voltage increases, the output frequency also increases.
Regards,
Danilo
Hi Danilo,
if he can use the LM331 voltage to frequency converter.
Below is two graphs captured from LM566's datasheet. It looks like it can operate up to 100kHz or the maximum sweep rate is up to 1MHz.
We have a very limited support in LM566. Do you know which part of function in LM566 that customer wanted to reproduce in LM331 (if it is possible). Please provide us the design requirements, perhaps we can figure it out how to assist the customer.
Best,
Raymond
Hi Raymond,
This is the design we are using for LM566
where,
VCO is given with control voltage (11.25V to 15V at pin5), Resistor & Capacitor and receive output frequency.
Example, V5=12.37, V+= 15, Ro= 2700, Co= 1uF
By the below mentioned formula (LM566)
fo= 155.8Hz (output frequency of LM566)
Regards,
Mirthun
Hi Mirthun,
if he can use the LM331 voltage to frequency converter.
It looks like if you can adjust some of R, C and Vin parameters, you should be able to replace LM566 with LM331. Since the pseudo simulation does not work with V to F conversion, I am unable to simulate it.
If you use the following calculated value, the output frequency should be approx. 155.85Hz with Vin = 2Vdc per the Vin to frequency transfer function.
I would suggest to place the LM331 on a perfboard or breadboard and check it out. 155.85Hz is in the low range of LM331 and it should work.
If you have additional questions, please let me know.
Best,
Raymond
Hi,
Could you confirm that whether we can use this internal IC diagram for the LM331 Simulation with Tina?
Regards,
Mirthunraju M
Hi Raymond,
As you mentioned "you should be able to replace LM566 with LM331". But according to our design if Vin increases, Frequency out should be decreases.
By the LM331 Formula,
I hope it is not possible. And also, according to our design Vin varies from 11V to 15V and respective frequency out should be received at Frequency out,
| Vin | Fout |
| 11 | 237.037 |
| 12 | 177.7778 |
| 13 | 118.5185 |
| 14 | 59.25926 |
| 15 | 0 |
Now, can you check whether LM556 is replaced with LM331?
Regards,
Mirthunraju M
Hi Mirthunraju,
If you use the following calculated value, the output frequency should be approx. 155.85Hz with Vin = 2Vdc per the Vin to frequency transfer function.
I mentioned that Vin needs to be approx. 2Vdc in order to work with LM331. The following upper equation is for LM566, which the fo is proportional to (V+ - V5). LM331's transfer function is different. You have to modify the modify the input voltage for LM331 and level shift the input is to the acceptable range.
BTW, if you plot out the attached data above, the Vin and Fout seems to be linear, except it sloped downward. Anyway, the circuit should work, except you have to lower the input voltage, Vin. You may use the voltage divider or op amp to level shift the LM566's Vin voltage.
If you have other questions, please let me know.
Best,
Raymond
Hi,
Vin of the LM566 is from P2(external) could be of maximum 15V. We tried to simulate the input voltage of Vin of LM566 and this what we observed,
So, this will be the Vin Voltage provided to the LM331.
could you confirm whether is it replaceable?
Hi Mirthunraju,
I do not have resources to check the physical setup in the lab. The LM331's V-to-F transfer function is published and shown in the image below.
However, I can request our technician to check on behalf of you. It will take approx. 7-10 days, please let me know if it is ok with you.
Best,
Raymond
Hi Mirthunraju,
I put the LM331 circuit together on the bench, and it works fine as the transfer function presented in the datasheet.
In my LM331 configuration:
Vin = 1Vdc --> frequency out is 118.5Hz or 8.438 msec in square wave
Vin = 2Vdc --> frequency out is 215Hz or 4.66 msec in square wave
Vin = 3Vdc --> frequency out is 308Hz or 3.24 msec in square wave
Vin = 5Vdc _--> frequency out is 515.5Hz or 1.94 msec in square wave
In LM566 IC, your inputs are sinusoidal, but V+ - V5 is a constant or DC voltage, if I understand your attached plot correctly (J1 and V5 are synchronized sinusoidal waveform).
If my understanding is correctly, you need to convert the input signals to DC voltage via a difference amplifier, which is the equivalent to Vin = (V+ - V5) function, where Vin_dc to LM331's input and (V+ - V5) is the signal differences from LM566.
If LM566's AC signals are converted to the equivalent DC voltage for LM331, then V/F conversion will be made.
Please let me know if my understanding of your circuit is correct.
Best,
Raymond
Hi Raymond,
As Vin of LM566 pin5 is ranges from 11.25V to 15V according to datasheet.
We don't know the exact P2 value. So, we use Sinusoidal signal to check to the Vin range of LM566 pin5. And ended up with the Vin range as 12.37V to 15V. According to this DC value 12.37V to 15V should generate respective frequency.
Whereas the DC Voltage value, which is provided to LM566 and same value will be provided to LM331.The LM331 frequency out should match with LM566.
Where LM566 and LM331 frequency out are differs in the linearity. So, LM331 could replace LM566 in this case?
Hi Mirthunraju,
Where LM566 and LM331 frequency out are differs in the linearity. So, LM331 could replace LM566 in this case?
The LM566 has different input Vcm range from LM331, but the LM566's transfer function is specified that fo is a proportional to (Vcc - V_pin5) (fo is linear to Vcc - V_pin5, see the captured figure below). If you are taking into account the delta voltage, LM566 has similar V/F conversion from LM331, which LM331 has different transfer function.
The Figure 15 below specified the linearity of LM331 part. The linearity should be good at low V/I conversion.
During the bench test, I used R and C that is close to previous LM331 155.85Hz simulation (C has tolerance up to ±20%, R is typically ±5%). LM331 can replace LM566 IC, if the input voltage of LM566 (Vcc - V_pin5) is translated to LM331's input in V/F converter.
If you have additional questions, please let me know.
Best,
Raymond
