Standby Power Reduction of Auxiliary Power Supply for Digitally Controlled SMPS 1.0.0

Everything you never wanted to know about switched-mode power supplies (SMPS)!

SMPS are used extensively in modern appliances because of their lower standby power consumption over linear power supplies. 

A switched-mode power supply (switching-mode power supply, switch-mode power supply, switched power supply, SMPS, or switcher) is an electronic power supply that uses a switching regulator, such as the TOP223Y pulse-width modulated switch found in many Samsung SMPS, instead of linear regulators to convert electrical power efficiently. Like other power supplies, an SMPS transfers power from a source, like mains power, to a load, such as a refrigerator, while converting voltage and current characteristics. 

Unlike a linear power supply, the pass transistor of a switching-mode supply continually switches between low-dissipation, full-on and full-off states, and spends very little time in the high dissipation transitions, which minimizes wasted energy. Ideally, a switched-mode power supply dissipates no power. 

Voltage regulation in an SMPS is achieved by varying the ratio of on-to-off time. In contrast, a linear power supply regulates the output voltage by continually dissipating power in the pass transistor. This higher power conversion efficiency is an important advantage of a switched-mode power supply. 

SMPS may also be substantially smaller and lighter than a linear supply due to the smaller transformer size and weight.

SMPS are more complicated than linear power supplies. Also, their switching currents can cause electrical noise problems if not carefully suppressed. This is why you will see EMI noise filters in appliances that use SMPS. The EMI filter is there to prevent this switching noise, called harmonics, from getting back into the mains power supply.  

Another drawback with SMPS is that simple designs may have a poor power factor which can be compensated for by other design configurations. 

This paper presents some of the design considerations for reducing the standby power consumption in SMPS.