Jump to content
Electronics-Lab.com Community
Sign in to follow this  
aniruddha

Please help on odd reference voltages

Recommended Posts

Why not use a Pot? You could set a reference voltage quite easily, and you should already have a rather stable power supply for your PIC


POT's.JPG

Wind the POT's to the required resistance and check them with a multimeter and your set.

If for some reason your voltage regulator decides to conduct harder/less than the voltage Vref (the reference for your ADC conversions) on your PIC is also going to be affected proportionally.

Eg; Vout from reg rises too 5.2 Volts, therefore the output of the potentiometers will rise by 0.2V but so too will what ever Pin (probably Vcc) you have as a reference for the ADC conversions, so your PIC will still read 2.26 or 3.673 volts (well the analogue equivalent), as its a digital representation of Vref

Share this post


Link to post
Share on other sites

Thanks, will try... have any specific pot for suggestion?
Will the pot give required accuracy?

I dont think stability would be a factor because after all its the ratio that counts ... temperature coefficients would get cancelled ... hence insensitive to temp. changes?

Share this post


Link to post
Share on other sites

If you are in no particular hurry, then I have a few TL431s and daughterboards I could spare.  They need two 1206 SMD resistors each for biasing.  They stand on edge and act like a two pin zener then finished.  PM me if you're interested.

Share this post


Link to post
Share on other sites

The accuracy will depend on where you set it - use a multimeter and wind too exactly where you want it, be sure to test the output without the screwdriver on the pot as the downward force may alter its normal reading.

The input impedance shouldn

Share this post


Link to post
Share on other sites

With the resolution you seek, standard values won't get you there in one step.  I recommend choosing one common value, and for the other leg combining resistors in parallel to trim the value down.

For example:  with a TL431 I would use a 10k 1% on the bottom leg which always sees a nominal 2V495, which I would measure with ref shorted to cathode.  For the upper leg I would start with 750R and measure the actual resistance.  After measuring the shunt voltage, expecting  2V655 to 2V709, I will know how far the '431 is off the nominal voltage and about how much reference current the chip needs.  Then I would select a resistor to parallel with 750R to get the target value of 516R to 729R, which could be from 1k6 to 26k.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
Sign in to follow this  

×
×
  • Create New...