Discussion in 'General Electronics Chat' started by pradeeba, Apr 11, 2008.
What are all the possible reasons for a SMPS not taking load?
The main reason is that it is more effiecient than a linear power supply and secondly it is lighter.
The inductance of the transformer wounded is not correct as per paper design.that time whether SMPS takes full load?
Can you rephrase what you mean by "takes full load?"
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.
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.
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
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.
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
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.
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!