SMPS load

Discussion in 'General Electronics Chat' started by pradeeba, Apr 11, 2008.

  1. pradeeba

    Thread Starter Active Member

    Feb 27, 2008
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    What are all the possible reasons for a SMPS not taking load?
     
  2. mik3

    Senior Member

    Feb 4, 2008
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    The main reason is that it is more effiecient than a linear power supply and secondly it is lighter.
     
  3. pradeeba

    Thread Starter Active Member

    Feb 27, 2008
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    The inductance of the transformer wounded is not correct as per paper design.that time whether SMPS takes full load?
     
  4. thingmaker3

    Retired Moderator

    May 16, 2005
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    Can you rephrase what you mean by "takes full load?"
     
  5. scubasteve_911

    Senior Member

    Dec 27, 2007
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    Maybe he means being able to supply current to a load, or the voltage dropping excessively upon loading? It's fun to guess ;)

    If this is the case, then it is mainly a function of how much energy you can store in the inductor.

    Steve
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    In the case of an SMPS for a PC, my first check would be the fan - does it run? If not, the supply has very likely been run at high temperatures for quite a while, which ages the components very quickly. The electrolytic capacitors commonly used in these supplies tend to go bad after a number of years of operation, much more quickly if run hot. If the supply has gotten REALLY hot, the insulation on the transformer/coil windings may have melted and the windings are now shorting together.
    Bad solder joints are another common problem, and some can be difficult to find. Repeated deep heating/cooling cycles can cause the metal to crystallize and fracture, much like what happens when you bend a soft drink can tab back and fourth a number of times until it breaks off. I've found broken solder connections on PCBs that were perfectly round (same size as the hole through the PCB) that I had to use high magnification to see - otherwise, they looked normal.
     
  7. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    You made some sense out of something I didn't have the foggiest idea about what was being asked.

    If the OP is trying to run the SMPS from a PC without having it in a PC, other causes for low output current could be that the Power_on pin is not being held low (nothing should run in that case), and/or there is no load on the 5V output (I think it is usually the 5V output, it may not matter). John
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    John, you're right about the 5v supply needing a couple of amps load to ensure proper regulation.

    I modded an ATX form-factor supply to use as a bench supply. Had to use a 10 Ohm wirewound resistor across the 5V output to get stable output on the other voltages.
     
  9. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Same here. I use an old ATX supply to power my LiPo and NiCd chargers. The problem is that some Dells use a different color code scheme than most ATX supplies; thus, I was reluctant to say which wire by color needed to be grounded or loaded. John
     
  10. SgtWookie

    Expert

    Jul 17, 2007
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    I didn't rely on my supplys' wire color codes either - I labeled each one as I cut them from the motherboard connector, and left the labels on. ;)
     
  11. RaoulDuke

    New Member

    Apr 11, 2008
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    Thats because the supply was made overseas......they don't know that "bad boys rape our young girls but violet gives willingly"

    But at least they know how to connect everything right!
     
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