100 -240 v ac power supply

Gadget

Joined Jan 10, 2006
614
Generally a 100 - 230volt down to 5 volt supply rectifies the mains voltage, then uses high frequency Switch Mode techniques to turn this high DC voltage into high frequency AC with a Mark Space ratio that is monitored and varied to ensure that the rectified output stays at 5 volts.
 

Gadget

Joined Jan 10, 2006
614
Normally a small High frequency transformer is used in switch mode PSU's to maintain isolation between the secondary and primary. Without this isolation there might be safety issues as well as tripping of Earth Leakage breakers (GFI).
 

bloguetronica

Joined Apr 27, 2007
1,372
Normally a small High frequency transformer is used in switch mode PSU's to maintain isolation between the secondary and primary. Without this isolation there might be safety issues as well as tripping of Earth Leakage breakers (GFI).
Agree, but normally it is a 1:1 ratio transformer to keep the volume of the PSU small (in some cases 2:1 ratio transformer is used).
 

Gadget

Joined Jan 10, 2006
614
I have never checked ratios, but wattage and core size would be constant no matter what the ratio.
I would have thought a step down ratio would be used otherwise the high frequency rectifier diodes on the secondary would have to be rated at over 350volts to cope with peak voltage, increasing expense..??? .. Also, if the output cap/filter failed would we get 350 volt DC pulses on the output...?

Efficiency increases with frequency and correct core selection, and that has more to do with physical size especially when you consider most SM PSUs operate anywhere up to 300kHz.
 

bloguetronica

Joined Apr 27, 2007
1,372
I have never checked ratios, but wattage and core size would be constant no matter what the ratio.
I would have thought a step down ratio would be used otherwise the high frequency rectifier diodes on the secondary would have to be rated at over 350volts to cope with peak voltage, increasing expense..??? .. Also, if the output cap/filter failed would we get 350 volt DC pulses on the output...?

Efficiency increases with frequency and correct core selection, and that has more to do with physical size especially when you consider most SM PSUs operate anywhere up to 300kHz.
Actually, a 1:1 ratio transformer is smaller than a step down transformer with the same wattage.
 
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