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Change the switchmode power supply's input voltage PDF Print E-mail

Changing the input voltage of a switch mode power supply
Would it be possible to modify a power supply designed for operation on 120 VAC for use overseas where the power is 240 VAC?
There are many factors involved in changing a power supply unless it is designed for dual voltage or autoswitching. They saved a few cents if it is not easily switched, what can I say?

The problem is that it is probably a flyback converter and these are pretty finicky about changes. In addition to the caps, and switching transistor, the transformer would probably saturate at the higher voltage unless the switching frequency were also doubled. Getting these things to work normally without blowing up is touchy enough. To change one without a thorough understanding of all the design parameters would be really risky.

Going the other way may be more realistic if (and this is a big if) you will not be running at anywhere near full capacity. Many switchmode power supplies will run on much lower than their rated input voltage. However, regulation may be poor and the switchmode transistor will need to be passing much higher current to maintain the same power output. To maintain specifications could require extensive changes to the circuitry and replacement of the switchmode transistor and possibly transformer and other parts as well. Again, I do not recommend this.

Use a small stepup or stepdown transformer instead. The only exceptions are:
If there are clearly marked jumpers to select the input voltage.

You can reverse engineer enough of the input circuitry to add/remove the needed connection with confidence.

CAUTION: As they say in wood-working: "Measure twice, cut once". Make sure you are dealing with the correct jumper AND you are going the right way (increasing or decreasing as needed). If the manufacturer didn't include this feature, there may be a good reason!
The supply is clearly marked as being autoswitching or having universal power input.

 
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