Description

Every year: millions of Watts are lost in heat from inefficient linear AC/DC wall adapters. This loss is incurred even when there is no load applied. The cause of this inefficiency is that energy is being lost from leakage elements found in the transformer and electrolytic capacitors. This reference design shows that by using a SMPS instead of a linear supply: you can drastically reduce the amount of wasted energy and by adding some additional circuitry that “wakes” up the supply when a load is applied: losses drop to a few milliwatts.The wake on load AC/DC power adapter is a wall mount power supply which converts 100-240Vac to 5Vdc at 500mA to a USB port. The typical application for this type of AC/DC adapter is a cell phone charger. The unique feature of this power adapter is extremely low power consumption when the output is not loaded. This power adapter uses Texas Instruments' LM5021 PWM controller and has a load detection and shutdown circuit which turns off the PWM IC at no load. It won’t restart until the output is loaded ( wake on load ) or the output capacitor is discharged to a certain level. The start up circuit is designed to consume less than 40uA current at high line input during shutdown period. By doing so: the no load power consumption of this adapter can be greatly reduced.