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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.

Inputs Output #1
  VinMin=100V     Vout1=5V  
  VinMax=240V     Iout1=0.5A  
  • Extremely low power consumption when the output is not loaded
  • 100 -240 Vac input range
  • Regulated 5V, 0.5A output
  • Design was assembled and tested


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Part Number Status

Load Detecting Power Supply


TI Devices (2)

Order samples, get tools and find more information on the TI products in this reference design.

Part Number Name Product Family Sample & Buy Design Kits & Evaluation Modules
LM5021  AC-DC current mode PWM controller  Offline & isolated DC/DC controllers & converters  Sample & Buy Not Available
LMV431  Low-Voltage (1.24V) Adjustable Precision Shunt Regulators  Voltage references  Sample & Buy View Design Kits & Evaluation Modules

CAD/CAE symbols

Part # Package | Pins CAD File (.bxl) STEP Model (.stp)
LM5021 Download Download
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LMV431 Download Download
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Technical Documents
User guides (1)
Title Type Size (KB) Date
PDF 931 27 Jan 2012

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