A brief discussion on the standby energy consumption problem and its power supply solution

1. Introduction

With the popularization of household appliances and audio-visual products, the widespread application of office automation and the continuous development of networking, more and more products have standby functions, such as battery charging, remote control, digital display, timing, touch and heat preservation functions, etc., to meet the needs of users at any time. These new products and new technologies have greatly facilitated our lives, but also caused a lot of energy waste. For example, the standby energy consumption of digital TV is about 1 to 5W, the standby energy consumption of set-top boxes is about 20 to 40W, the standby energy consumption of personal computers and monitors is about 5 to 10W, and the standby energy consumption of mobile phone chargers is about 0.5 to 1W. According to a survey by the Organization for Economic Cooperation and Development, the energy consumed by countries due to standby accounts for about 3% to 13% of the total energy consumption. The statistics are: Australia is about 12%, South Korea is about 11%, Germany is about 10%, the United Kingdom is about 8%, Japan is about 7%, the United States is about 5%, and Finland is about 5%. At present, the average standby energy consumption of urban households in my country has accounted for about 10% of the total household energy consumption, which is equivalent to each family using a 15~30W "eternal lamp". Standby energy consumption is like an invisible blood-sucking worm, which wastes energy and creates huge environmental pressure.

In 2000, the International Energy Agency (IEA) launched the energy-saving initiative "1 Watt Plan" to global electrical product manufacturers and sellers, which has now received positive responses from the European Union and the United States. By 2010, the standby power consumption of all electrical products exported to these regions must be reduced to 1 watt, which will become a new non-tariff barrier for all electronic product manufacturers that have entered or attempt to enter the European and American markets.

2. Survey on the current status of energy consumption of electronic appliances in standby mode

"Standby energy consumption" refers to the energy consumption of electrical equipment with standby function when it is not in use and the power is not disconnected. Electrical equipment with standby energy consumption mainly include air conditioners, computers and communication systems (including computer host, display screen, computer audio, printer, scanner, charger, router, etc.), home video and audio systems (including TV, DVD, VCD, audio, amplifier, set-top box, satellite receiver, etc.). In order to avoid the trouble of frequent plugging and unplugging of electrical appliances, or to save the settings of the use status of electrical appliances, many users are accustomed to using the remote control to conveniently close the electrical appliances without disconnecting the power supply, so that the electrical appliances are in standby state for a long time. While the standby function provides convenience for residential users, it also causes a lot of energy waste.

According to a recent survey conducted by Shanghai Electric Power Company, the total standby energy consumption of the three major household appliances in the city, air conditioners, home video and audio systems, and computers and communication systems, is about 700 million kWh. If, on average, 468 grams of raw coal is consumed to generate 1 kWh of electricity, more than 300,000 tons of raw coal will be wasted. The 700 million kWh of standby energy consumption each year directly causes consumers to waste about 300 million yuan in electricity bills [1].

According to statistics from the European Commission, in 2005, 3.7 billion products with standby/off modes were installed in the 25 EU countries, which would cause 47 trillion watt-hours of standby/off power consumption, equivalent to 6.4 billion euros in electricity bills. It is estimated that by 2010, the annual standby/off power consumption of electronic and electrical products in the EU will rise to 62 trillion watt-hours. If EU member states take appropriate measures to reduce standby energy consumption, 39 trillion watt-hours of electricity will be saved between 1999 and 2010.

3. Domestic and international standby energy consumption standards

Since the International Energy Agency proposed the "1 Watt Plan" for standby energy consumption of electronic appliances in 2000, standby energy consumption of electronic appliances has received increasing attention. Voluntary agreements on standby energy consumption by enterprises, the US "Energy Star" certification, and government mandatory regulations have been introduced one after another. As a major exporter of electronic and electrical products, my country must be familiar with and understand these agreements and regulations, reduce product standby energy consumption, and overcome the technical barriers to standby energy consumption.

In 1992, the U.S. Environmental Protection Agency (EPA) and the Department of Energy launched the "Energy Star" project, which is not mandatory. Manufacturers who voluntarily cooperate with this plan can put the "Energy Star" logo on their qualified products once their products meet the "Energy Star" energy efficiency requirements. The earliest products that cooperated with this plan were mainly computers and other electrical appliances, and then gradually extended to motors, office equipment, lighting, home appliances, etc. The "Energy Star" program has become one of the international standards. Now, there are 28,000 different types of terminal energy-consuming products in the world that have obtained the Energy Star energy-saving certification, and more than 1 billion Energy Star products are sold each year. Since November 2008, the second edition of "Energy Star" has been implemented, stipulating that the standby power consumption of the power adapter must be less than 0.3W or 0.5W, depending on the output power of the adapter.

In December 2007, the United States enacted the "U.S. Energy Independence and Security Act of 2007", which established the first mandatory federal energy efficiency standard for electrical appliances and lighting products. Its content is basically the same as the requirements of the "California Energy Commission Appliance Efficiency Regulations of 2007" promulgated by the California Energy Commission (CEC). South Korea announced that it would implement mandatory measures for products with standby energy consumption of less than 1W in 2010, and is currently the first country to implement mandatory measures. Australia announced that by 2012, the standby energy consumption of all its electronic and electrical products will be less than 1W. On July 8, 2008, the European Commission announced the implementation regulations of Directive 2005/32/EC on Ecodesign, which aims to reduce the energy consumption of all household and office electrical and electronic equipment when they are turned off and in standby mode [2].

In November 2008, the world's major mobile phone suppliers, Nokia, Samsung, LG, Motorola and Sony Ericsson, jointly announced a new and stricter standby rating system for mobile phone chargers, which exceeds the current or proposed standby power consumption standards of any organization in the world today. According to Nokia, the power consumed by mobile phones in standby mode accounts for more than 60% of their total power usage. The new rating system will use a zero to five star logo pattern to distinguish standby power consumption. For example, mobile phone chargers with standby power consumption less than or equal to 30mW belong to the highest star rating and have five stars printed on their labels. On the contrary, if the standby power consumption is ≤500mW, there will be no star mark on the charger label. We can make a comparison: for chargers with the same output power, the most stringent maximum no-load power consumption stipulated in the new version of the "Energy Star" EPS2.0 specification is 300mW, which can only be rated as two stars if the new star standard is used for rating.

4. Analysis of the standby power consumption mechanism of switching power supplies

At present, most electronic devices below 100W, such as power adapters, chargers, cordless phones, ADSL routers, LCD monitors and DVDs, etc., use offline flyback switching circuits to convert the 85V~275V AC power provided by the power grid into the DC voltage required by electronic devices. Under normal working conditions, the losses of flyback switching power supplies mainly include conduction losses and switching losses, as well as control circuit losses. In standby mode, because the output current of the system is close to zero, the conduction loss can be ignored, and the switching loss and control circuit loss become the main system standby power consumption. To reduce standby power consumption, we should focus on reducing switching losses and control circuit losses.

Figure 1 shows the main loss types of the flyback switching power supply in standby mode, among which the power tube switching loss, drive loss, transformer core loss, output rectifier tube reverse recovery loss and buffer loss are all switching losses. All types of switching losses are related to the switching frequency. Reducing the switching frequency can reduce switching losses. The loss of the control circuit is mainly manifested as the loss on the starting resistor, and the loss of the starting resistor is directly related to the rectified DC bus voltage and the starting resistor value. Under the working condition of ensuring a wide voltage input, the starting resistor loss can be reduced by reducing the starting current.

5. Low power standby power solution

As a leading power management integrated circuit manufacturer, BCD Semiconductor Manufacturing Co., Ltd. (BCDSemi for short) has long been committed to the development and research of high-efficiency, low standby power consumption green power solutions.

As early as 2004, BCDSemi took the lead in launching a "green power" controller, AP384xG, which is fully compatible with the industrial standard PWM controller 384x and has an intermittent low standby function. The most obvious difference between AP384xG and the standard PWM controller 384x is that it has an internal controllable current source, which is charged by the current source to increase the comparison level of PinCS to achieve intermittent working mode under light load conditions to reduce standby power consumption. At the same time, AP384xG also specially designed a low startup current circuit to reduce the startup current from the typical 200uA to 40uA, greatly reducing the loss on the startup resistor.

Due to special design considerations, AP384xG is fully compatible with the standard PWM controller 384x, providing a so-called "Plug-and-Play" "green power" solution. Without modifying the original design, users can replace 384x with AP384xG and adjust a few resistor and capacitor parameters to significantly improve power conversion efficiency (55%~65%) and reduce standby power consumption (3.25W~0.5W), successfully passing the "Energy Star" energy-saving certification [3]. Due to its significant energy-saving effect and compatibility, AP384xG has been widely used in DVD power supplies, CRT/LCD display power supplies, electric bicycle charging power supplies, etc. To date, more than 50 million units have been sold, saving nearly 130 million kWh of electricity for society.

As the world's leading mobile phone charger solution provider, BCDSemi launched the AP376x series, an ultra-low standby power charger solution that meets the most stringent five-star standards, in June 2009. Its no-load power consumption below 30mW enables manufacturers to easily meet all global charger/adapter energy efficiency and no-load specifications, including Energy Star EPSv2.0.

AP3768 is a representative product of the second-generation primary-side controller produced by BCDSemi. In addition to continuing the successful architecture of the first-generation products, its design eliminates expensive but low-reliability peripheral components, achieves high-precision output voltage/current control, and ensures a ±5% output voltage/current tolerance range under system mass production conditions. AP3768 integrates a more precise adjustable cable compensation function, allowing customers to achieve compensation for any voltage value by adjusting the value of an external resistor to meet the application of output cables with different wire diameters and lengths. Its patented "Sub-μA Startup" technology and low operating current are the technical guarantee for achieving 30mW ultra-low standby power consumption.

Figure 2 shows the typical application circuit and main characteristic curves of AP3768.

a) Application circuit

b) Output characteristic curve

c) Efficiency curve

d) No-load standby curve

According to NOKIA's estimates, if the world's 3 billion mobile phone chargers can adopt the above-mentioned five-star standard technology and achieve a standby power consumption of less than 30mW, it can save society nearly 1.2 trillion watt-hours of electricity each year [5].

References:
[1] Wang Kang, Research and Countermeasures on Standby Energy Consumption of Household Appliances in Shanghai, Power Supply and Use, Issue 2, 2007
[2] Yu Jianfeng, Overcoming the Technical Barriers of Standby Energy Consumption of Electronic Appliances, China Energy, Vol. 31, No. 3, 2009
[3] Wu Xin, Offline Green Power Control Chip AP384xG, Electronics and Computers, Issue 01, 2005
[4] BCD Semiconductor Manufacturing Co., Ltd., AP3768 Product Data Sheet, www.bcdsemi.com
[5] NOKIA, “Charger Energy Rating”