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Author Topic: 0-30volts Lab power supply  (Read 2551 times)
pier
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« on: April 24, 2007, 11:52:20 AM »

I have made the 0-30 volts lab power supply which is there on this site . I want to know if it was possible to add a FINE TUNE provision for accurate selection of the O/P voltage . Please help me .
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shafton
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« Reply #1 on: April 25, 2007, 10:26:57 PM »

I dont think it is possible, or else the author would have done that .
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audioguru
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« Reply #2 on: April 25, 2007, 10:58:54 PM »

Hi Pier,
Of course you can add a fine tuning pot. Just add it in series with the existing pot. Make it have a value less than the existing pot. You might need to reduce the value of the existing pot a little.
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pier
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« Reply #3 on: April 26, 2007, 01:25:10 AM »

Thanks a lot AG , I was about to wind up after shaftons reply . Will this changes be sufficient ?
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esp1
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« Reply #4 on: April 26, 2007, 01:49:23 AM »

hi pier,
Assuming that the existing 10K pot gives you a linear range of 0 to 30Vout, then the 100R [centred] will give you a +/- 0.15V adjustment, that should be OK.
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pier
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« Reply #5 on: April 26, 2007, 08:59:22 AM »

hello esp1
               Actually i just guessed with no practical calculations . But since u say its going to be fine i just have to try it out . But since AG said you should reduce the value of the existing pot as well, I am confused .
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audioguru
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« Reply #6 on: April 26, 2007, 09:57:37 AM »

The 10k resistor provides an output voltage range of from 0V to about 34 (but the project can't go that high). Since 100 ohms is 1/100th of 10k then its fine tuning range is from 0V to only 0.34V. The 10k pot doesn't need to be changed.

This is the voltage setting pot which is a voltage divider. I was thinking about adding another fine tuning pot in series with the current setting pot which would change the amount of current and require a lower resistance for the original pot so the total resistance is correct.

Many people found the voltage and current of the project reachs max before the pots are at max. They fix it by adding calibration trimpots in series with the existing pots.
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pier
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« Reply #7 on: April 26, 2007, 10:46:12 AM »

Hi AG
        So is the 100 Ohms pot fine for the fine tune . What should be the value if i need to get a fine tune of one volt ?
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Ante
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« Reply #8 on: April 26, 2007, 12:38:12 PM »

I use this type (10-turns) of potentiometers for PSU
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audioguru
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« Reply #9 on: April 26, 2007, 12:53:42 PM »

So is the 100 Ohms pot fine for the fine tune . What should be the value if i need to get a fine tune of one volt ?
If 10k ohms gives 34V then 10k/34= 294 ohms gives 1V.
It won't be accurate since pots have a tolerance of 20%.
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pier
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« Reply #10 on: April 26, 2007, 10:48:16 PM »

Thanks for the value AG but is it a standard value that we get ? . I feel ante's selection is a good one but do you call them a multiturn pot ? or does it have a specific name  Huh ?
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shafton
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« Reply #11 on: April 26, 2007, 10:55:57 PM »

sorry for wrong information

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audioguru
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« Reply #12 on: April 27, 2007, 07:27:41 AM »

Pots are made only in certain resistance values and their resistance has a tolerance of about 20%. So you won't get one that is 294 ohms. Maybe 200 ohms and 500 ohms are the closest.
Use a multi-turn pot instead like Ante uses.
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Ante
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« Reply #13 on: April 27, 2007, 10:30:40 AM »

For these multi-turns I try to find heavy machined aluminum knobs with a small crank or one with a finger hole; this gives you a smooth and accurate feeling.
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