display | more...

A Switch mode power supply(smps), is a more advanced power supply than the (usually black) ones you are used to just plug in the wall. It is much more efficient, up to 80-90% of the input power is transformed into output power. As opposed to the older models that have an average output efficiency around 30-40%.
SMPS is the kind of power supply found in your PC.
The way it works is pretty simple:
If you have 10V input and you want 5V output, the SMPS cuts the 10V into eg. 10V in ½ a second and 0V in the remaning ½ a second, then the SMPS filters the pulsating current into 5V continous current, and thereby only using circa half of what a conventional power supply would use.

Switch mode power supplies are a relatively modern (since the 1970's) way of converting one voltage into another. They are lighter than the older power transformer based supplies, as well as more efficient. This higher efficiency leads to less heat production as well. Switching power supplies are also more flexible; some of them can accept a wide range of input voltages so that 120/240 switches are not necessary. Just plug it in, let the power supply figure it out.

The theory of operation is simple. The input voltage is rectified and filtered, then used to drive a high frequency oscillator. The frequency is generally much higher than the range of human hearing. The output of this oscillator is then fed into a transformer, which converts the voltage appropriately. Since the frequency is so high, this transformer can be much smaller and lighter than the kind required to convert 60Hz alternating current.

The output of this transformer is then rectified and filtered with large capacitors. Some of the output is also fed into the oscillator, where it regulates its frequency. As the oscillator frequency changes, so does the output voltage; this forms a feedback loop which keeps the output voltage constant regardless of load. (Provided the load doesn't become excessive, that is.)

The downside to switch-mode power supplies is that they can generate spurious high frequency interference. This is the reason they are generally not used in high end audio equipment; filtering out the interference becomes costlier than simply using a low-frequency transformer and filter caps the size of melons.

Log in or register to write something here or to contact authors.