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A voltage booster without capacitor

  1. Aug 31, 2008 #1
    Hello i just want to know if it's possible to do 5V with a 1.5V battery without any capacitor

    Thanks
     
  2. jcsd
  3. Sep 1, 2008 #2

    berkeman

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    Are you familiar with the boost topology DC-DC? Why do you not want an output smoothing cap? What is the application that you have in mind?
     
  4. Sep 1, 2008 #3
    I have to run a 4.8V DC motor with a 1.5V battery. The motor is used to propulse a little car.
     
  5. Sep 1, 2008 #4

    berkeman

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    Look at the Simple Switcher boost DC-DC circuits at National Semiconductor:

    http://www.national.com/analog

    Click on the design helper at the right of the page, and input your voltage and current requirements. The calculator will help you design the circuit. You can generally buy the parts from Digikey.com

    You should also calculate how long the motor will run on that 1.5V battery. Assume about 85% efficiency for the boost stage (the National calculator may guesstimate the efficiency for you -- I'm not sure if it will), and check the A*Hr rating of the 1.5V battery. BTW, when you spec the input voltages for the calcultor, keep in mind that the range for an alkaline battery is about 1.65V fresh, and 0.8V mostly gone. Other battery types will have different discharge curves. Check the battery manufacturer websites for datasheets.

    I think the calculator will provide you with an output capacitor value. I'm still not sure why you don't want to have a cap at the output. If you still have questions after using the calculator, post them here and we'll try to help.
     
  6. Sep 2, 2008 #5
    This is very good but i want to know if it's possible tu use the booster without capacitor. it's a constraint.
     
  7. Sep 2, 2008 #6
    In example: is it possible to use this boost converter without the cpacitor if not what will happen
     
  8. Sep 2, 2008 #7
  9. Sep 2, 2008 #8

    berkeman

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    You tell us. What is the function of the capacitor in the standard boost DC-DC converter circuit? What happens as you make the capacitor larger, or smaller?

    There are at least two effects of decreasing the output capacitor size. Can you tell us what they are?

    Why do you have this constraint? Is it coming from someone who does not have an understanding of electronics? Or is it being posed as an advanced puzzle by someone who knows of an elegant non-standard solution?
     
  10. Sep 3, 2008 #9
    it is posed as an advanced puzzle by someone who knows of an elegant non-standard solution. It's like a challenge. so i have to find a way to do 5V with a 1.5V battery without any capacitor.
     
  11. Sep 3, 2008 #10

    chroot

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    You'll need some kind of reactance, but it doesn't have to be capacitance. You can build a voltage multiplier with inductors, too -- they're just larger and heavier and more expensive.

    - Warren
     
  12. Sep 5, 2008 #11
  13. Sep 5, 2008 #12

    Redbelly98

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  14. Sep 5, 2008 #13
    Thank you chroot for your advice it worked. And yes chaoseverlasting i could run the motor with 1.5v but it was also a question of speed.
     
  15. Sep 5, 2008 #14
    You cannot use an actual capacitor or you can't have any appreciable capacitance in the circuit? I ask becuase you can be clever and use some coax as some capacitance in the circuit.
     
  16. Sep 5, 2008 #15

    mheslep

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    'Puzzle', 'non-standard', and 'challenge', and the fact that you have specifically not specified 'DC', just 5 V, lead me to believe that your tasker intended some kind of pulse waveform be used which is plausible w/ a motor load. You can drive the motor with some kind of 5V pulse waveform. The DC/DC boost converter (referenced above) with no output capacitor with give you a pulse waveform, and the duty cycle of the converter would control the motor speed.
     
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