LM331 V-F Design, Please Help.

[StudentSA]

I am nearing the end of one of my electronics projects, however I have hit a problem and I really need help in designing a suitable linearity V-F.

I have requested help before while still familiarising myself with the LM331 in this post:
LM331 Post

I have now established my requirements and specifications.

I need the LM331 to be setup as a V-F with 0V = 0Hz and 10V = 30kHz
10V full scale = 30Khz
The supply will be a 12V Regulated supply.

Here is the problem ... In the datasheet
- The basic circuit given is only configured for 0 to 10kHz after which all hell breaks loose (linearity). I do not require excellent linearity just suitable i.e 1% or so

- The precision circuit is 0-100kHz but requires + and - voltage supply. I would like to keep things simple and only use a +12 Volt supply. Also this circuit is somehow designed for -10V full scale input.

On a side note I was keen on using the AD654 ... looks amazing but I cannot source this IC at a reasonable price in SA. The Lm331 is my second best option.

Can anyone please help me design a circuit using only +12V that meets my requirements

Regards,
StudentSA

 

[MRCecil]

Take a look at National's datasheet below. There should be no problem with a 12V supply. It would be just a matter of a quick calculation and building it.

https://www.electro-tech-online.com/custompdfs/2010/06/LM231.pdf

 

[StudentSA]

I will take this approch and try the simple design in Figure 3 of the datasheet.

I have choosen values
Ct = 10nF
Rt = 10k
Rl = 50k
Rs = 31350 this will be a fixed with a series 10k pot

I will attempt this build later, my concern however from previous experiments was the linearity at higher frequency demands.

Let me recheck and get back.

Thanks,
SSA

 

[MRCecil]

Pay close attention to the datasheet notes concerning the types of components. Use metal film 1% (E96) resistors, COG/NPO 2% MLCC ceramic capacitors where appropriate and a proper layout. If these cautions are followed, you should be able to get 0.5%-1% linearity even on a breadboard (given appropriate changes in Rt & Ct to compensate for the inherent reactance).