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Non-linear CV/CC control in schematic
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coromonadalix:
another control variant

Velleman kit  k7200
Silver_Pharaoh:

--- Quote from: xavier60 on March 03, 2019, 02:02:38 am ---
--- Quote from: Silver_Pharaoh on March 03, 2019, 12:54:01 am ---
--- Quote from: duak on March 02, 2019, 07:58:43 pm ---If you want a linear output voltage adjustment, change it to something like the attached image where only the upper portion of the voltage divider is variable.

Cheers,

--- End quote ---

I cannot for the life of me figure this out! I've tried connecting pin 4 to the top leg of the pot & the wiper, no luck.
Tried moving the pot over to pins 5&6 like I see in the LM723 datasheet, no luck - I have no control over voltage at all.

I'm missing something here....


I've also been reading about getting voltage control down to 0V with the LM723, it seems I need a negative voltage fed into the error amplifier of the LM723..... Not sure how that will play out.

--- End quote ---
It would be better to have a fixed divider from the output terminals to the error amp's inverting input. The Pot then is used to adjust the reference to the non-inverting input.
Applying a small positive offset to the inverting input will allow the output to be adjusted to a lower voltage.

--- End quote ---

the error amp's inverting input is pin 2, which is connected to the current adjustment pot, so I'm not sure how to connect up the voltage adjust pot if the current adjust pot is connected to pin 2?
xavier60:
I meant the voltage error amp's input pins, 4 and 5.
duak:
Silver, what is your present voltage control circuit?  The linear Vout adjust I presented works very well.

If you want the output voltage to go down to zero, you will have to provide a negative supply voltage to pin 7 of the 723 or figure out a way to operate the 723's core with voltages offset from the actual output voltage.  The latter can be done with some reference diodes such as the LM385.
Silver_Pharaoh:

--- Quote from: xavier60 on March 03, 2019, 05:10:49 pm ---I meant the voltage error amp's input pins, 4 and 5.

--- End quote ---
Ahh, I must have misread. Thansk for clarifying, I will give it another go  :)


--- Quote from: duak on March 03, 2019, 05:13:48 pm ---Silver, what is your present voltage control circuit?  The linear Vout adjust I presented works very well.

If you want the output voltage to go down to zero, you will have to provide a negative supply voltage to pin 7 of the 723 or figure out a way to operate the 723's core with voltages offset from the actual output voltage.  The latter can be done with some reference diodes such as the LM385.

--- End quote ---

Currently, the top leg of the pot is connected directly to pin 3 which is Vout, the wiper comes from pin 4, the inverting input (which is coupled to pin 13 with a capacitor) and the other leg of the pot goes to ground where pin 7 connects.

I've attached a picture of the current schematic
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