Design Specifications
| Inputs |
Output #1 |
| VinMin=100V | Vout1=5V |
| VinMax=240V | Iout1=0.5A |
Design 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 National Semiconductor’s
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.
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Design Resources
Additional Product Resources
| • |
LM5021
- AC-DC Current Mode PWM Controller |
| • | LMV431 - Low-Voltage (1.24V) Adjustable Precision Shunt Regulators |
- datasheet
- application notes
- samples
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Board Photo
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Features
- 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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