LM331

tjs2010

Member
2010-09-29 12:48 pm
Anyone here have any experiance using the LM331 as a F/V converter?

I have it breadboarded up as per the data sheet, these are te results i got from it.

Freq Voltage out (mV) Increment
100 0.03 ............. 200 0.03 0 300 0.05 0.02 400 0.08 0.03 500 0.1 0.02 600 0.1 0 700 0.13 0.03 800 0.14 0.01 900 0.17 0.03 1000 0.18 0.01 1500 0.28 0.1 2000 0.37 0.09 2500 0.46 0.09 3000 0.55 0.09 3500 0.64 0.09 4000 0.72 0.08 4500 0.77 0.05 5000 0.84 0.07 5500 0.89 0.05 6000 0.95 0.06 6500 1.04 0.09 7000 1.13 0.09 7500 1.2 0.07 8000 1.3 0.1 8500 1.39 0.09 9000 1.5 0.11 9500 1.59 0.09 10000 1.68 0.09 10500 1.81 0.13




As you can see the output is really low, from research I have looked at it should roughly go up 1V per Hz... another weird thing is that the circuit works as above even when I turn off the power supply which makes me think something weird is going on. Any ideas?
 

tjs2010

Member
2010-09-29 12:48 pm
My table 'cut n paste' seems to have failed horribly, what I was trying to illustrate is that it is only rising about 0.09 mV per 0.5kHz squarewave rise. i.e from 0.37mV to .46mV ...Seems like the chip is getting any power to use to convert??

I have it setup with a PSU on 15v.
 

tjs2010

Member
2010-09-29 12:48 pm
Cheers David, noone semed to know the answer to the question before!

I figured out the answer to the problem above regarding the output voltages i was receiving.

Power wasnt succesfully getting to the chip due to a faulty cable,

A new problem arose when i fixed it though.

The output now remains consistantly at around 14v (input is still 15V)

Im hoping that the chip is just buggered.

I have ordered a new LM331 (The AN model this time), and hopefully this should sort it's self out straight away. (fingers crossed at least!)

I will write my results up here tomorrow after I have fully tested it with the new chip.