Connect with us

More Range From 10 turn POT

Discussion in 'General Electronics Discussion' started by MrClamperSir, Mar 11, 2016.

Scroll to continue with content
  1. MrClamperSir

    MrClamperSir

    72
    7
    Feb 3, 2016
    I've got 2 questions:

    1. How can I get more range from my 10 turn POT? Before reading any further, please note that my potentiometer in my actual circuit is connected at 1 and 2 only. Right now I'm getting all the power my circuit is capable of within 1 turn.
    2. Do I need (or is it best) to add a diode in this circuit for protection? If so, do I connect it to the IC or at the end of the circuit?
    Thank you pp.jpg
     
  2. Alec_t

    Alec_t

    2,950
    803
    Jul 7, 2015
    It's not ideal, but you could try getting better adjustment by connecting a ~1k5 resistor between pins 1 and 2.
     
    MrClamperSir likes this.
  3. AnalogKid

    AnalogKid

    2,497
    718
    Jun 10, 2015
    Your question is very low in detail. More range - more than what? What is the "range" now? AND, kinda important, what range do you want?

    IF you are saying that the circuit output goes from minimum output to full output in only 1 turn of a 10 turn pot
    AND IF you are stuck with that 10 turn pot
    THEN connect pin 2 to pin 3 AND connect a fixed resistor to pins 1 and 3 as above.

    The result will not be a linear adjustment, but it will have more "range".

    ak
     
    MrClamperSir likes this.
  4. Bluejets

    Bluejets

    4,772
    999
    Oct 5, 2014
    Try a 5K or smaller pot.
    Is there any load connected?
     
    MrClamperSir likes this.
  5. MrClamperSir

    MrClamperSir

    72
    7
    Feb 3, 2016
    Thanks you. That's exactly what I'm saying. I'm going from minimum output to maximum output in 1 turn.

    I'm not stuck with the 10 turn pot necessarily but it would be a great asset to the overall design so I can better fine tune the power to my tools.

    What's the difference between linear and nonlinear in regards to put the fixed resistor across the pot?
     
  6. MrClamperSir

    MrClamperSir

    72
    7
    Feb 3, 2016
    Thank you. I tried the 5k pot initially and it did give me more of the dialing range I was looking for. Maybe I should try a lower valued pot?
     
  7. Bluejets

    Bluejets

    4,772
    999
    Oct 5, 2014
    If you read the spec sheet for the 338 it will show how the calculation for the adjustment come about.

    What about the load, any load connected or is the output floating?
     
  8. MrClamperSir

    MrClamperSir

    72
    7
    Feb 3, 2016
    My original question was a result of using the circuit with load. I believe when there was no load the pot would operate closer the range I was expecting. Meaning it was taking many full turns to get the voltage from min to max
     
  9. Bluejets

    Bluejets

    4,772
    999
    Oct 5, 2014
    What is the load?
     
  10. MrClamperSir

    MrClamperSir

    72
    7
    Feb 3, 2016
    Hmmm well I'm super new to this whole thing so sorry for sounding dumb but I'm not sure what that means exactly. I'll take a stab at it though.

    The tool I was using was drawing 4.5-5.5V at just over 0.5A
     
  11. dorke

    dorke

    2,342
    665
    Jun 20, 2015
    Yes it is advised to add the protection diodes.

    What are you going to use this P.S supply?
    Fixed voltage with "fine adjustment"?
    Variable output voltage?
     
    MrClamperSir likes this.
  12. MrClamperSir

    MrClamperSir

    72
    7
    Feb 3, 2016
    PSU with a Variable output
     
    Last edited: Mar 12, 2016
    davenn likes this.
  13. Bluejets

    Bluejets

    4,772
    999
    Oct 5, 2014
    Just trying to find out as much info as I can here........
    So you are running a 4.5v - 5.5v load from a 16v ac supply , rectified and then through a variable regulator that gives " all the power my circuit is capable of within 1 turn "

    Trying to determine what problem you have with that.

    Do you need a fine adjustment control as well?
     
    MrClamperSir likes this.
  14. MrClamperSir

    MrClamperSir

    72
    7
    Feb 3, 2016
    Exactly. The unit works well for what I'm using it for but it would be nice to fine tune the adjustment and also just so o can wrap my head around the whys and whatnot.

    Thank you.
     
  15. Bluejets

    Bluejets

    4,772
    999
    Oct 5, 2014
    It's just that by my estimates, your 16V AC will become approx. 22V DC, drop a couple of volts across the regulator, say leaving approx. 20v.
    Regulator will start around 2V out, so 18v adjusted by a 10k pot so maybe 1.8V per turn so after 1 turn approx 4V out....see what I'm getting at?
    You said you load is between 4.5V and 5.5V so at 1 turn I'm guessing you would be near max for the load.
    Or did I get it wrong somewhere?
     
    MrClamperSir likes this.
  16. MrClamperSir

    MrClamperSir

    72
    7
    Feb 3, 2016
    That's just about how it operates in real life!! That's awesome. I'm terrible at math and therefore equations so it's been tough trying to realize this project but once I build something I can learn it.

    I know on my other supply where I'm using the 317 amplified by a transistor I can dial the voltage a lot finer. It takes three or four spins just to get it in the lower operating range. I guess I was thinking this would operate similar.

    But that has a 24V in and a 5k pot so maybe that contributes to the function
     
  17. dorke

    dorke

    2,342
    665
    Jun 20, 2015
    There is another thing you can try set R1 to 240ohm.
    It will double your "turn ratio".

    BTW,
    an odd point,
    The LM338 is capable of 5A, yet you are using a 2A transformer, why is this?
     
    Last edited by a moderator: Mar 12, 2016
    MrClamperSir likes this.
  18. MrClamperSir

    MrClamperSir

    72
    7
    Feb 3, 2016
    Thank you. I will give that a try.

    I only need up to 1A on the output. I'm trying to not overload or overbuild this thing but optimize my needs and keep everything as cool as possible. A lot of guys have gone to switchmode cause it's small and lightweight. I think they are made of cheap components and tend to break easier.

    I like the linear cause it's heavy and durable. I don't really like the heat from it so I'm trying to keep the input closer to the output.
     
  19. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    If you are trying to keep the heat to minimum, and you need a max of say 6V, you should reduce the voltage of the transformer. Using a 9V transformer instead of 16 would reduce the heat produced by almost half.

    Bob
     
    MrClamperSir likes this.
  20. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    And, as for your original problem. The range of voltage you can get with a 10K pot goes up to 105V! No wonder you use only 1 turn out of ten. Use a 1K pot, which will max out at 11.6V or a 500Ω which will max at at 6.4V. See calculator here:

    http://diyaudioprojects.com/Technical/Voltage-Regulator/

    Bob
     
    MrClamperSir likes this.
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-