Electronics > Projects, Designs, and Technical Stuff
Non-linear CV/CC control in schematic
<< < (5/10) > >>
xavier60:
My most recent experience was with the SG3525. Its error amp works with the input common mode range down to 1V.
I would aim for about 1.5V minimum on the Inv pin on the LM723.
I don't have the IC to experiment with.
With the Ninv pin floating I would find what minimum voltage is needed on the Inv pin to keep the Comp pin pulled low.
duak:
To work properly the 723 requires a minimum of 2 volts between the both the inverting and non-inverting inputs and pin 7.  It may work lower but performance may suffer.  Your circuit violates this by allowing the non-inverting input to go to 0 volts.  Try exchanging R1 and the Vadjust pot and recalculating the values.  In the limit, the non-inverting input will vary between Vref (~7.15 V) and whatever your voltage divider delivers.  The 723 then tries to deliver an output voltage equal to the ratio of R21/(R20+R21) times the non-inverting input voltage.  With the present values or R20 and R21 it will be 11X the voltage on the non-inverting input.

Does this make sense?
xavier60:
I would start with a 4:1 divider, 15K/4.7K. 10K from Vref to Inv should set the 2V minimum.
Use something higher like 10K for the voltage adj Pot and use it as a  variable divider not as a VR
Silver_Pharaoh:

--- Quote from: duak on March 03, 2019, 06:58:50 pm ---To work properly the 723 requires a minimum of 2 volts between the both the inverting and non-inverting inputs and pin 7.  It may work lower but performance may suffer.  Your circuit violates this by allowing the non-inverting input to go to 0 volts.  Try exchanging R1 and the Vadjust pot and recalculating the values.  In the limit, the non-inverting input will vary between Vref (~7.15 V) and whatever your voltage divider delivers.  The 723 then tries to deliver an output voltage equal to the ratio of R21/(R20+R21) times the non-inverting input voltage.  With the present values or R20 and R21 it will be 11X the voltage on the non-inverting input.

Does this make sense?

--- End quote ---

Not fully no...

Inv & NInv pins should both have a difference of 2V between them and pin 7 correct? So those pins should be connected to Pin 7 with a voltage divider to ground? (Pin 7 is usually connected to ground no?)

I tried swapping R1 and the pot leaving everything else alone and no luck. When you say recalc the values, I assume you mean R20 & R21?
The last bit about Vout being X times the NInv voltage makes sense.


--- Quote from: xavier60 on March 03, 2019, 07:22:36 pm ---I would start with a 4:1 divider, 15K/4.7K. 10K from Vref to Inv should set the 2V minimum.
Use something higher like 10K for the voltage adj Pot and use it as a  variable divider not as a VR

--- End quote ---

I tried this, but I wasn't able to get anything to work....


So bottom line here is Inv pin and NInv pins should be connected together? What about Pin 7 (-V?)


A physical picture example would probably help me. I don't learn so well from just text unfortunately. I need to see something hands on to grasp it.
xavier60:
I drew this up quickly. Ill check for possible mistakes later.
The values aren't supper critical.
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod