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| Non-linear CV/CC control in schematic |
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| 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. |
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