DC power supply

Discussion in 'General Electronics Chat' started by vick5821, Jun 22, 2012.

  1. vick5821

    Thread Starter Member

    Jan 27, 2012
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    Hey friends, I plan to build a DC power supply for my future usage of electricity to replace battery.

    I plan to use the adapter(Approximate 16 -18V) as input and I plan to use voltage regulators too -- 7805, 7806, 7809, and 7812( Common source of voltage)

    My concept is like this :

    I plan to have a DC power supply and a switch so that I can adjust to the voltage output that I need. For eg, I want 9V, so I make the 9V available by adjusting the switch. What most important is, I plan to have only ONE output terminal and not 4 output terminal(As it will be messy) So it means when I want 6V , I adjust it to be 6V at the output. And when I want 9V, I adjust it to be 9V that will be appearing at the output terminal

    This is my initial sketch of my circuit :
    [​IMG]

    In this sketch, I will add diode 4007 before the Vin of the regulator and PLAN TO ADD 4007 diode too at the Vout of regulator. But placing diode in the Vout of regulator cause me one problem - Diode has voltage drop of apporximate 0.7V. This means when the Vout is 5V, the exact voltage at the output terminal will be only around 4.3V.

    Any ideas on how to overcome this and any more suggestion on implementing this DC power supply circuit ?

    Thank you :)
     
  2. ronv

    AAC Fanatic!

    Nov 12, 2008
    3,281
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    Here is what I would do since you only want 1 output at a time.
    All the regulator inputs and grounds can be common to your unregulated supply.
    Then you need 1 ground output and 4 separate voltage outputs. If you build it in a nice little box you can then just move the positive lead to the voltage you need.
     
  3. w2aew

    Member

    Jan 3, 2012
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    A simpler implementation would be to use something like an LM317 adjustable voltage regulator, and use the switch to configure the resistors used to program the output voltage. Only one regulator IC, instead of several, and no worries about diode isolation. Of course, even a 7805 can be used with resistors to create a higher supply voltage, similar to the LM317, except that 5V is the voltage between the OUT and "adj" terminal. Just watch your power dissipation, and be sure to add the recommended filter caps before and after.
     
  4. radiohead

    Active Member

    May 28, 2009
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  5. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Just use an LM317 with a "potentiometer" to adjust the output voltage.
     
  6. #12

    Expert

    Nov 30, 2010
    16,248
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    Add a 470 ohm resistor from the output pin to the ground pin, then add a diode from the junction of the 470/ground pin to ground.
     
  7. vick5821

    Thread Starter Member

    Jan 27, 2012
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    I do not want the adjustable type. I want it to be adjust to a fixed value output like 5V, 6V, 9V and 12V
     
  8. vick5821

    Thread Starter Member

    Jan 27, 2012
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    Can you provide me with a diagram on what you mentioning about ?

    Thank you
     
  9. vick5821

    Thread Starter Member

    Jan 27, 2012
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    I do not get what you mean ? LM 317 is the adjustable type already. And how I make use of the resistor and switch in this case ?

    Thank you
     
  10. #12

    Expert

    Nov 30, 2010
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    1 diode interferes with the output voltage, 1 diode raises the output by the voltage used up by the first diode.
     
  11. vick5821

    Thread Starter Member

    Jan 27, 2012
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    How it does that ? Detail explanation about the connection method ?

    Thank you
     
  12. Wendy

    Moderator

    Mar 24, 2008
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  13. #12

    Expert

    Nov 30, 2010
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    I told you how the second diode compensates for the voltage loss caused by the diode on the output. I gave you a drawing of the connection method. If you can't understand these, maybe you shouldn't be playing with electricity.
     
  14. vick5821

    Thread Starter Member

    Jan 27, 2012
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    Oh ya. Didnt noticed about that. Thank you :)

    btw, I mean HOW does it rasied thee voltage by the voltage used by the diode that intefers with Vout ? I mean HOW
     
  15. absf

    Senior Member

    Dec 29, 2010
    1,490
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    Read the datasheet on page 23 fig 12.

    Allen
     
    Last edited: Jun 23, 2012
  16. vick5821

    Thread Starter Member

    Jan 27, 2012
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    0
    [​IMG]

    My latest sketch. Using 2 DPDT switch. In this case, I know the output voltage is not only 5,6,9 and 12, it can be the combinational of the 5,6,9 and 12 for the output too. Is this a good idea ?

    Thank you
     
  17. Sensacell

    Well-Known Member

    Jun 19, 2012
    1,127
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    If you want to keep it *simple* just leave all the regulators powered and have a rotary switch that switches between the different outputs. The only drawbacks are: (a) The quiescent power consumption of the unused regulators. (b) The consumption of money you need to spend using multiple regulators.
     
  18. vick5821

    Thread Starter Member

    Jan 27, 2012
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    I do not want the others regulator is being power up when I want to use a specific regulator only. I aware that by using LM 317, I am able to get adjustable output voltage. That I will include in my project too and besides that, I wwould like to have another option where I can have a fixed 5V, 6V, 9V and 12V output. :)
     
  19. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
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    may I ask what is the current you intend to draw from this power supply?
     
  20. vick5821

    Thread Starter Member

    Jan 27, 2012
    54
    0
    I never thought of that. I think for normal electronic project usage only. perhaps not too small and not too big. Any suggestion ? I thought if the voltage is fixed, the current will be fixed also ? I can choose what current value for certain value of voltage ?
     
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