ControlBooth
Wiki

SMPS Printable version

https://www.controlbooth.com/wiki/SMPS

This page has been seen 1,080 times.

Switched (or switch-) Mode Power Supply.
JD;191065 said:
Switch-mode refers to the power supply type that is used in the LED fixtures. It is the same type of power supply that is used in computers. I just checked the Wiki and there was not a listing, so here is a brief description of how they work. AC power comes into the unit and goes to a rectifier, which converts it to DC. From there, it is stored in a filter capacitor. This provides a continuous source of DC power to the pulse-width-modulated (PWM) driver transistor. This transistor is turned on and off at a very high speed (Thus the name "Switch-Mode") and drives a small power transformer. Because of the high frequency it is switching at, the transformer can be very small. The secondary is rectified and provides the DC power to run the fixture. There is a feedback circuit that monitors the output voltage, and modifies the pulses that are firing the transistor to provide more of less drive as needed.

Here's the important part- Since the first two parts in the chain are a rectifier and a capacitor, input power is only drawn near the peak of the AC waveform. In other words, unlike a resistive load like a regular lamp, the current draw is not sinusoidal. This is why computers (which use the same type of supply) and back-up power supplies are rated in VA instead of watts.