jmke

Switched mode power supplies work by rectifying alternating mains current and then driving a high frequency transformer with pulses of this rectified current.

The high frequency transformer produces a high frequency output which is then rectified and smoothed by filter capacitors.

The advantages of this approach are that a small, lightweight transformer can be used instead of a big iron cored mains frequency transformer, and very little standby current is required when no load is being drawn.

Two of the major downsides are that the high frequency pulses of current are rich in harmonics which can produce broadband RF noise, and that the ripple in the DC output of the high frequency transformer output can cause heating in the smoothing capacitors used to condition the DC output before it makes it way to the electronics being powered.

http://www.ahars.com.au/htm/hb_switchmodePSRepair.html

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geoffrey

Bad caps are very often the reason for a broken LCD power supply.

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