Designing a power supply that works both in continuous and discinuous conduction!!

Discussion in 'General Electronics Chat' started by supermankid, Feb 8, 2014.

  1. supermankid

    Thread Starter Member

    May 26, 2013
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    Hi all,

    I want to design a power supply for FPGA, where the core current can vary from few milliamps in sleep mode to about 16 Amps at maximum core usage. I have investigated a lot of switching regulators. Is there any pit fall that should be considered while designing the power supply which runs in both light load and very high load. Do the regulator in market can handle these cases easily or do I have to consider other special techniques??

    Thanks for sharing your knowledge.

    Nice weekends everyone!!
     
  2. MrChips

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    Oct 2, 2009
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  3. supermankid

    Thread Starter Member

    May 26, 2013
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    Mr Chips, I was talking about inductor current ripple. #12s stuff is pretty not related to my question(though useful info). I hope you understand my question.
     
  4. MrChips

    Moderator

    Oct 2, 2009
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    Sorry, then I don't understand the question.

    If you need a power supply to deliver 16A @ 5V then that is what you need.
     
  5. paulktreg

    Distinguished Member

    Jun 2, 2008
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    I'm with MrChips. You need a power supply capable of 5V @ 16A. If your load only requires a few mA then that's all that it will supply.
     
  6. crutschow

    Expert

    Mar 14, 2008
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    Some control chips are designed to handle small loads in discontinuous mode, which would be stated in the data sheet or description of the chip. I don't know off-hand which those are so you'll have to search. TI and Linear Technology are two good places to start. Discontinuous mode can cause more ripple in the output voltage if the circuit isn't designed for that.
     
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  7. t06afre

    AAC Fanatic!

    May 11, 2009
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    You can add a resistor as fixed load. To ensure that the current draw never drop below a point there the regulator will "fail" perhaps combined with some indicator LEDs on your board. You should always find the minimum current draw in the power supply datasheet
     
  8. supermankid

    Thread Starter Member

    May 26, 2013
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    Thanks Mr. Crutschow. This was what I was talking about. Is there a some kind of trick to minimize ripple output voltage. If I have enough phase margin of y power supply, can I assure that it will work fine in both continuous and discontinuous mode?
     
  9. crutschow

    Expert

    Mar 14, 2008
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    I think for best operation in discontinuous mode you need a controller specifically designed to handle that mode. Don't know of any other tricks to minimize output ripple except to increase the output inductor and/or capacitor value. But it should still be stable if you have sufficient phase margin, although the output pulse rate may become somewhat erratic. Note that the ripple in the discontinuous mode may still be entirely acceptable for your application requirements.
     
  10. supermankid

    Thread Starter Member

    May 26, 2013
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    Thanks a lot. I needed some direction to start my investigation. You are the man of the day :)
     
  11. t06afre

    AAC Fanatic!

    May 11, 2009
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    Then some power supplies are not loaded with a specified minimum load. They voltage may go outside the setpoint. A quite common problem for a designer to take into consideration
     
  12. inwo

    Well-Known Member

    Nov 7, 2013
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    Seems a tiny linear supply for sleep mode would make sense.

    That's what tvs do. Starting the main supply on wake-up.
     
  13. ronv

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    Nov 12, 2008
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  14. THE_RB

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    What FPGA draws 16 amps?? :eek:

    Is that some kind of instantaneous peak current? That's what decoupling caps are for.

    And if the average current is indeed 16A, then what is the peak current?

    You really need to supply better info if you want help with the PSU design. :)
     
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