Design tips and application solutions for very low standby power adapters - Power Circuit - Circuit Diagram

DFN1006 TP-RCLAMP3321P ESD Diode Low Capacitance

Brand AVX TPSE226M035R0125 Low impedance tantalum capacitor AVX 22

MOS power IC full range

Industrial Router Crystal 3.2*2.5mm 3225 26M (26.000MHZ) 12PF 10PPM 20PPM 30PPM

Photocoupler

Power adapters are widely used in notebook computers, game consoles, printers, DSL modems, and mobile phones. From the point of view of people's usage habits, these devices also have a considerable proportion of time in light load or standby (no load) mode of operation. Therefore, the “ENERGY STAR” and other standards are focused on improving the energy efficiency of the power adapters used in these devices, while also focusing on improving light load energy efficiency and reducing standby energy consumption.

For example, the US Environmental Protection Agency (EPA) version 2.0 ENERGY STAR External Power Supply Specification (EPA 2.0) further enhances energy efficiency requirements based on version 1.1 (see Table 1), where Ln is the natural logarithm of the rated output power.

Table 1: Specification for 1.1 and 2.0 versions of the US Environmental Protection Agency's ENERGY STAR external power supply.

The power levels of different adapters vary widely, and power supplies with power greater than 75 W require increased power factor correction (PFC) according to IEC61000-3-2 and other requirements, and less than 75 W. This article focuses on the features required for power sub-75 W adapters to meet the new EPA 2.0 specifications, as well as ON Semiconductor's high-performance, energy-efficient controllers that provide these required features.

Ways to meet energy efficiency regulations

To meet the above specifications for the external power supply operating efficiency and standby energy requirements, we first need to analyze the source of the loss. In fact, in terms of working loss, there are two main aspects, namely switching loss and loss caused by leakage inductance. These two types of losses can be quantified by equations (1) and (2), respectively:

Equation (1)

Equation (2)

It can be seen from these two equations that there are two ways to improve the energy efficiency of the work: one is to reduce the switching frequency (FSW), that is, to use the frequency back-off technique at light loads; the other is to reduce the drain voltage at the time of shutdown. (VDRAIN (turn-off)), corresponding to the valley switch technology.

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