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Voltage controlled oscillator VCO

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New Member
Hi, i need a voltage controlled oscillator and reading in my textbook there is an example how to make one using a frequency to voltage converter. They use a LM331 IC and i have attached the circuit the textbook shows.

I have a LM2907 frequency to voltage converter and would like to use this instead of the LM331 (which i dont have). (The LM2907 datasheet doesnt have a VCO example so i cant follow that) Is it ok to use this instead of the LM311 in its circuit?
Assuming it is, i'm unsure of what pins on the LM2907 correspond to the pins on the LM331 VCO circuit.

I have the 14 pin LM2907N

My guess so far at the pins are:

LM331 pins = LM2907 pins

1 3
2 11
3 5
4 12
5 4
6 2
7 10
8 8

To be honest these really are just guesses, i don't understand the workings of either the LM331 or LM2907 sufficiently to make a proper guess and suspect i can't use the LM2907 to replace the LM331.

Any help would be appreciated

(both datasheets also attached)




Well-Known Member
The LM331 is a voltage to frequency converter. The LM2907 is Frequency to voltage converter. In the LM331 it outputs a frequency based on a voltage (note, in data sheet the 331 can also be used a FV conv.). The LM2907 outputs a voltage based on frequency input.


New Member
If you were in the US, I could send you a handful of LM331's just for the mailing costs! I have them surplus at work!

Unfortunately, to send them to the UK would cost more than they are worth!

Farnell doesn't carry them?

The LM331 is a neat device, it can do V to F and F to V conversion and is very stable.I have made a lot of money through the years using it!


Well-Known Member
Most Helpful Member
A CD4046 phase locked loop IC has a VCO that you can use.
The datasheet for the LM324 has an audio VCO circuit.


New Member
I bought the lm2907 instead of the lm331 because it was cheaper, from farnell. :eek:
I've learnt my lesson i guess. The CD4046 sounds like a good option as i can get one from my local electronics store unlike the lm331 which i'd have to order online.

thank you for all your help guys.


In electronics like most everything else, (except perhaps hi-fi audio but lets not go there ;)) you get what you pay for.


New Member
I went and got a 4046, works a treat. Much simpler to use than i was expecting too. 1 resistor and 1 capacitor to get a VCO from 0Hz to upto 2Mhz with 10v Vdd amazing! :D


Good, you've managed to overclock it, the datasheet says it only works up to 1.3MHz with Vdd = 10V.


New Member
actually i havnt been over 20khz yet, and i was quoting the philips datasheet i have which says minimun 1 Mhz typical 2Mhz at Vdd = 10v although i'm not confident i havnt misread it!


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