Need help with this.

Discussion in 'The Projects Forum' started by jecker10, Jan 20, 2015.

  1. jecker10

    Thread Starter New Member

    Jan 20, 2015
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    I am currently woking on trying to run a power supply to a device at 10, 25 and 100% duty cycle. The only way I have found that I cando this is through PWM, if so can anyone help with a basic circuit ithas to be able to handle 13.5v. If there is another way to do this I am all ears.
    Thanks
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    What power supply? what type of device?
    Max.
     
  3. crutschow

    Expert

    Mar 14, 2008
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    What current?
     
  4. Ramussons

    Active Member

    May 3, 2013
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    Time period of the "Cycle" ?
     
    ebeowulf17 likes this.
  5. Evil Lurker

    Member

    Aug 25, 2011
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    Duty cycle is measure of time proportionate to time on and time off. In theory you could use a electromechanical relay to turn a device on for 6 minutes and on again in another 54 minutes and you would have a duty cycle of 10%. The same could be said if your relay was turned on for one minute and off for 9 minutes. However if you want to go faster than a mechanical switch can turn on and off or if you are turning something off and on again a lot your gonna have to use PWM.
     
  6. jecker10

    Thread Starter New Member

    Jan 20, 2015
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    The power supply is a DC power supply, I am not sure what the device is at the moment(this is for work and another guy has the request I am just supposed to build something to help with the power setup), the current is whatever the device takes which I am not sure what it is. The tme period of the cycle has to vary, I realize there are a lot of unknowns and variables but they want something that can affect the duty cycle of a power supply that is adjustable so that th duty cycle can be altered as required.
    Thanks
     
  7. jecker10

    Thread Starter New Member

    Jan 20, 2015
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    Got more information, the frequency of the PWM is 20Hz
     
  8. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    How accurate do the 10% and 25% have to be?
     
  9. jecker10

    Thread Starter New Member

    Jan 20, 2015
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    Within 10% but because this is being recorded would perfer to be on the mark.
     
  10. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Is the 20Hz already available (e.g. as a time reference), or does that have to be generated too? If you need to generate it, how accurate must the frequency be?
     
  11. jecker10

    Thread Starter New Member

    Jan 20, 2015
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    The power has to be on
    -13.5V DC for 4 min @ 100% duty cycle
    -13.5V DC for 26 min @ 25% duty cycle
    -13.5V DC for 30 min @ 10% duty cycle

    I will have to generate the 20Hz signal in whatever setup I have to make
     
  12. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    With that specific timing this project cries out for a micro-controller, which would also be able to handle the PWM generation and drive a MOSFET to switch power to the load.
     
  13. jecker10

    Thread Starter New Member

    Jan 20, 2015
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    I have a controller to output voltage so if I have to make multiple devices and have the controller switch between them then that is what I will do. Was hoping for something that would simply control the duty cycle but if i have to use a micro controller I do have my Arduino at home I can bring to work.
     
  14. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    There's no have to. Just more convenient. If you're a glutton for punishment you could do all the timing, the PWM generation and the duty cycle control/switching with discrete logic :).
     
  15. jecker10

    Thread Starter New Member

    Jan 20, 2015
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    Right, I am just gathering all of the information I need so that I can present the options to my boss. This seems easy enough using an Arduino and a MOSFET to run the duty cycle.
    Thanks
     
  16. wayneh

    Expert

    Sep 9, 2010
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    Since you are not looking for continuous control of the duty cycle (like most folks want went, for instance, dimming LEDs) you could use a 4017 counter to get preset levels with good precision. Choosing any single digit at the output would get you 10% duty cycle. ORing together 2 digits would give you 20%, and so on.

    I can't think how you would get 25%, but 20% or 30% would be trivial.

    Oh wait, if it's only counting to 4, then a single digit is 25% duty. So you could hit whatever values you need by just setting DIP switches.
     
  17. crutschow

    Expert

    Mar 14, 2008
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    But counting to 4 would not give a 10% duty cycle.

    You can get a 25% duty-cycle while counting to ten if the input clock has a 50% duty-cycle, by using an added D flip-flop, clock inverter, and triple OR-gate.
    Connect the inverted clock to the FF Clk input and the counter output O1 to the FF D input.
    ORing Q0, Q1, and the FF Q output gives a 25% signal.
     
  18. wayneh

    Expert

    Sep 9, 2010
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    Right, that's why I was thinking you would need DIP switches to allow setting the count-to value as well as choosing the outputs. If the OP only needs those 3 values plus 100%, it shouldn't be hard to figure out the switch settings.
     
  19. crutschow

    Expert

    Mar 14, 2008
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    That would work if the change in PWM frequency with duty-cycle is not a problem (or the clock frequency can be changed along with the change in the count).
     
  20. jecker10

    Thread Starter New Member

    Jan 20, 2015
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    Looking at all options but I think the MOSFET with the Arduino should be easiest, if I am right. I have most of the items I would need for it already, if i am wrong and someone knows an easier way then I would be grateful for that info.
    Thanks for all the help
     
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