ATX power supply and microcontroller

Discussion in 'General Electronics Chat' started by buzaiandras, Feb 21, 2012.

  1. buzaiandras

    Thread Starter Member

    Jul 18, 2011
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    0
    Hi,

    I need to power a PIC microcontroller (PIC16F688) from an ATX power supply (SMPS) of a PC and I have some concerns about this.
    How bad/good is to power a microcontroller from an SMPS power supply?
    What effects will the ripple (+-5% ripple) have on the workings of the microcontroller? Unfortunately I can't use a linear regulator.
    So I would like to find out more about how ripple affects the workings of the microcontroller.

    Thank you,

    Buzai
     
  2. spinnaker

    AAC Fanatic!

    Oct 29, 2009
    4,866
    988

    Isn't that overkill? The PSU is capable of supplying far more current than the MCU will ever hope to use.
     
  3. buzaiandras

    Thread Starter Member

    Jul 18, 2011
    54
    0
    The MCU will no be the only current consumer. It will be mounted inside a PC.
    Anyway I would like to know how the ripple affects the MCUs in general.
    Is it ok to power MCUs from SMPS power sources? Does the ripple cause the MCU to behave erratically? How exactly? Unfortunately I could not find much information about this on the internet.

    Thank you,

    Buzai
     
  4. MrChips

    Moderator

    Oct 2, 2009
    12,415
    3,354
    If the chips on a PC can handle the +5V supply from the ATX power supply then your MCU will be fine. Just make sure you have 0.1uF and 10uF capacitors across the power and ground lines.
     
  5. Felo

    Member

    Feb 20, 2012
    91
    13
    Yup, decoupling and stabilizing capacitors should be enough, I had some PIC's sucking power out of ATX's before, no problems so far.
     
  6. debjit625

    Well-Known Member

    Apr 17, 2010
    790
    186
    ATX PSU are specially designed to work with standard digital components and mcu comes under them.ATX SMPS is totally perfect for microcontrollers, just use some capacitors greater than 10 mfd to filter it ,as when other sections of motherboard are switching it may cause a brown out reset of your mcu sometimes.


    It doesn’t matters how much PSU can supply current ,it matters how much the load will consume at a particular voltage level, if the mcu is rated to work with 5VDC ,then you can use a power source of 5VDC with any amount of current ,of course it should be greater than the rated over all current of the mcu.


    For that it has already been said about filtering, MrChips said use a 10 mfd and 0.1mfd to filter it. If your mcu is consuming large current i.e.. its output pins are driving larger loads then use a capacitor greater than 10 mfd ,i normally use 100 to 220 mfd and remember try to put the 0.1 mfd capacitor close to the power pins of your mcu.


    It depends how much ripple you are talking about...normally with minor filtering ripples from an ATX PSU is acceptable for mcu stuffs.

    Good Luck
     
  7. @android

    Member

    Dec 15, 2011
    178
    9
    I've a query! What exactly are you planning to do? PIC inside your CPU?? Why?
     
  8. tmd_63

    Member

    Oct 20, 2008
    13
    0
    To make it run faster and more energy efficient.
     
  9. @android

    Member

    Dec 15, 2011
    178
    9
    May I know how?
     
  10. buzaiandras

    Thread Starter Member

    Jul 18, 2011
    54
    0
    Thank you all for your replies.

    The maximum ripple would be +-5% of the 5V line (it is a standard ATX PSU).
    So the peak-to-peak maximum ripple should be 500mV, right?.

    Actually I am creating a hardware module to start/stop the PC (media center) from a SONY remote control.
    So far I have done all the test with a regulated linear power supply and it is working properly. But before I install it inside the PC I needed to know if there are any problems running the MCU on a SMPS power supply.
    Also I am interested about how a SMPS power supply affects the MCU behavior, for my general knowledge.

    By the way: the IR receiver shouldn't be affected by the ripple, right? :) (filtered with capacitors).

    Thank you,

    Buzai
     
  11. debjit625

    Well-Known Member

    Apr 17, 2010
    790
    186
    Right,250mV peak that gives us 500mV p-p

    While considering the power supply, just remember that whatever power supply you use the voltage level of the power supply should be within the allowed voltage range of the mcu.Now for example my PIC18F4502 have a voltage range of -0.3V to +7.5V
    so -/+ 500mV on 5V will not affect my mcu,yes it could create noise in the circuit so we can filter it with capacitors.

    Yes it will be not affected,even without filtering it will work if you are running it with an ATX PSU.

    Good Luck
     
  12. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,733
    759
    Using a Freakin PIC....:D
     
  13. buzaiandras

    Thread Starter Member

    Jul 18, 2011
    54
    0
    Thank you :)

    Buzai
     
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