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Adjustable Power Supply Question

Doghouse

Aug 26, 2020
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Hello,

I have been reading a few posts and this seems like a friendly place for a novice to ask for advise. I am working on a bench power supply project and have a question about using coarse and fine adjustments for the current and voltage. The basic design comes from https://www.instructables.com/id/DIY-Lab-Bench-Power-Supply-Build-Tests/. One thing I don't like with this project is the use a 10 turn pot to adjust the output voltage and current. I would prefer to use coarse and fine controls like the circuit below:

IqdvQ.png


The voltage part of this makes sense to me, but I am not sure if this will work for the current. Please let me know the best way to implement coarse and fine adjustments for the current.

Thank you in advance.
 

Bluejets

Oct 5, 2014
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Don't know why you would not "like" a multiturn pot.
Perhaps the cost has put you off.

Your circuit is not using adjustable controls on the 100K and does not look correct.

Regardless, (without any circuit diagram to refer to) I'd imagine each pot would need to be in series with separate outputs.
 

Doghouse

Aug 26, 2020
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Don't know why you would not "like" a multiturn pot.
Perhaps the cost has put you off.

Your circuit is not using adjustable controls on the 100K.

Regardless, (without any circuit diagram to refer to) I'd imagine each pot would need to be in series.

It's a personal preference. Mutiturn pots annoy me. Sorry, wish I had a better answer, but that's the truth.
 

donkey

Feb 26, 2011
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my advice is as a novice too.... what about 2 pots in serial. one with your course and one with your fine adjustments. as long as the overall resistance is kept.... just a thought
 

Bluejets

Oct 5, 2014
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my advice is as a novice too.... what about 2 pots in serial. one with your course and one with your fine adjustments. as long as the overall resistance is kept.... just a thought

My thoughts as well, however, in wiring , care must be taken to ensure the Op doesn't end up with a dead short when the pots are screwed full one way.
 

Harald Kapp

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Nov 17, 2011
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The page where you took the schematic from gives all the math required. Current limiting is usually set by adjusting a reference voltage to a comparator circuit such that whenever the voltage sensed across a sense resistor exceedss the reference voltage current limit will set in, Therefore this circuit should work for current limiting, too. You may have to adjust the values of the potentiometers and resistors to match the potentiometer value present in the original circuit.
Another circuit including a thorough explanation is here.

As for the "design" you linked to: I came to really hate this kind of "design" as unfortunately seen rather often on instructables. Understanding or even modifying a circuit without a circuit diagram is not an easy feat when no circuit diagram (schematic) is being offered. I do respect the effort put into the presentations by the authors on instructables, but most of these "design" should be taken as is. They are meant for novices without sufficient background to really understand how the circuit works - less even how to modify it.
 

Doghouse

Aug 26, 2020
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Aug 26, 2020
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The page where you took the schematic from gives all the math required. Current limiting is usually set by adjusting a reference voltage to a comparator circuit such that whenever the voltage sensed across a sense resistor exceedss the reference voltage current limit will set in, Therefore this circuit should work for current limiting, too. You may have to adjust the values of the potentiometers and resistors to match the potentiometer value present in the original circuit.
Another circuit including a thorough explanation is here.

As for the "design" you linked to: I came to really hate this kind of "design" as unfortunately seen rather often on instructables. Understanding or even modifying a circuit without a circuit diagram is not an easy feat when no circuit diagram (schematic) is being offered. I do respect the effort put into the presentations by the authors on instructables, but most of these "design" should be taken as is. They are meant for novices without sufficient background to really understand how the circuit works - less even how to modify it.
Thank you for your answer.

I appreciate the advise, but not the condescending opinion.
 
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