Would this be a good DC Voltage supply

Discussion in 'The Projects Forum' started by Kuki Muki, Apr 3, 2018.

Would it be a good voltage source.

  1. Yes

    0 vote(s)
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  2. No

    2 vote(s)
    100.0%
  1. Kuki Muki

    Thread Starter New Member

    Apr 3, 2018
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    Currently i am making DC Voltage source that would be able to produce about 34V at output,the problem is that some people said that voltage will drop when resistance is above 100k,here take a look:
    Screenshot_1.png
    Well i am still a begginer in electronics,so please dont judge me.
    I added those resistors to limit the current to prevent short circuit.
    Also i need to use voltage doubler because electric components are hard to find here in Serbia,so i use what i found.
    Do i even need the fuse?
    R2=R3
    And i couldnt find AC source so i placed the DC source and marked it as AC.
    Thanks for help.
     
  2. ericgibbs

    Moderator

    Jan 29, 2010
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    hi Kuki,
    Welcome to AAC.
    The resistors are not a good idea.
    What Voltage and Current are you requiring from the power supply output.?
    What is the VA rating of the transformer.?
    Eric
     
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  3. Kuki Muki

    Thread Starter New Member

    Apr 3, 2018
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    Well i am not going to need more than 1A at output,but transformer rating is 3.2VA,and why are resistors are bad idea,i am going to use those up to 5W
     
  4. ericgibbs

    Moderator

    Jan 29, 2010
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    OK,
    The 1N4148 are not suitable diodes, those are considered signal diodes, you require rectifier diodes, for example 1N4001, which are rated at 1Amp.
    What rectifier diodes can you get.?
    E

    EDIT:

    A 3.2VA transformer at 12V is approx 250mA maximum current
     
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  5. AlbertHall

    AAC Fanatic!

    Jun 4, 2014
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    And for 1A output, C1 and C2 need to be much larger value.
     
  6. Kuki Muki

    Thread Starter New Member

    Apr 3, 2018
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    I have much better ones i have BY398 https://diotec.com/tl_files/diotec/files/pdf/datasheets/by396 which can survive much more than 1A

    Oh i know,i didnt change it default capacitance,it is going to be about 1000uF
     
  7. ericgibbs

    Moderator

    Jan 29, 2010
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    hi Kuki,
    This image shows what you require to get approx 24V at 500mA.
    E
     
  8. AlbertHall

    AAC Fanatic!

    Jun 4, 2014
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    Note that the 10MΩ resistor is needed to get the simulation to work. Do not fit this resistor when you actually build the circuit.
     
  9. ericgibbs

    Moderator

    Jan 29, 2010
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    Hi Kuki,
    This simulation shows a typical variable regulated Vout supply, using a LM317 voltage regulator.
    Note what Albert points out regarding the 10meg.

    E
     
  10. Kuki Muki

    Thread Starter New Member

    Apr 3, 2018
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    How do i then regulate the voltage with LM317?
     
  11. ericgibbs

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    Jan 29, 2010
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    hi,
    R3 in my diagram is a 2.5K potentiometer.
    For my simulation I set it to 1K for a test.
    You adjust the pot, at zero Ohms it gives 1.3Vout and when set to 2.5K it gives a Vout of 24V, or any value you set in between. OK.?
    E
     
  12. Kuki Muki

    Thread Starter New Member

    Apr 3, 2018
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    Why do i need C5 and C6?
     
  13. ericgibbs

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    Jan 29, 2010
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    Most voltage regulators are recommended to have low value capacitors close to the regulator in order prevent instability problems.
    E
    ESP1 04-Apr-18 11.35.gif
     
    Last edited: Apr 4, 2018
    Kuki Muki likes this.
  14. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
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    Without some kind of electronic regulation circuit, the output of your supply will have a large amount of ripple imposed on the DC voltage. Also, this ripple will increase as the load on the supply draws more current. Also, the output voltage DC value will vary wildly as the load draws more or less current.

    Series and shunt resistors do cause the output voltage to be adjustable - on paper. In practice, they are the worst possible way to adjust a power supply's output voltage.

    ak
     
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  15. marcf

    Member

    Dec 29, 2014
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    You need a DC supply capable of supplying 34VDC at 1.0AMP.

    Correct?

    You could make a 40 VDC 'brute force' (unregulated) power supply quit easily.
     
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  16. Kuki Muki

    Thread Starter New Member

    Apr 3, 2018
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    Could i then use transistor as a potentiometer(controling the voltage with potentiometer at its base)?
     
  17. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
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    Yes. The regulation will be poor, but much better than none at all. Depending on the output transistor, you might need significant base current, requiring a large pot. Better to use a discrete or packaged Darlington.

    ak
    [​IMG]
     
  18. Kuki Muki

    Thread Starter New Member

    Apr 3, 2018
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    Today i tried mine circuit w/o pots and i got much greater voltage that i thought 43V !But still current was about 150mA without any load except R4,and yes it was 5W not 2W resistor so i think it will be a good current limiter,for my uses as a hobyst,and Thanks for answering!
    Also could i use something instead of D1 on your schematic,because in Serbia there is almost no radio shops.
     
  19. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
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    The schematic in post #17 is just to illustrate how a pot and darlington-connected transistor forms a voltage regulator. You can change all of the parts to whatever you can find locally. Pay attention to power dissipation in R1 and Q2.

    ak
     
  20. marcf

    Member

    Dec 29, 2014
    215
    34
    Hello

    What voltage range are you interested in obtaining?

    Do you just want to adjust the output to 37 Volts?

    Is there a plus or minus limit?

    I am not seeing a lot of lm317 circuit examples for output voltages of greater than 37volts due to the lm317's input voltage limit of 40 Volts.

    There is a lm317HV version that has a input voltage limit of 60V.

    There is also the heatsink problem to contend with.
     
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