DESIGN & PRODUCTS POWER DESIGN How low can you go? Driving down standby SOLAR MIDGET FUSE HOLDERS ® power in next-generation adaptors By Grant Floyd FROM THE CHARgINg of a tablet PC or smartphone battery requirements. The Energy Policy and Conservation Act (EPCA) to powering a laptop computer or home router, power adap- of 1975 established that any new energy conservation stan- tors have established themselves an essential part of everyday dard must be designed to achieve the maximum improvement life. For the consumer electronics OEMs that bundle these in energy efficiency that is both technologically feasible and adaptors with their products there are two key driving factors economically justified. Therefore, the standards are typically not that need to be addressed. These are ensuring high efficiency representative of ‘best in class’ performance. Many power sup- levels, meeting safety regulations and simultaneously having a ply manufacturers are requesting that no load power be limited compact form factor. In recent times, thanks to a combination as much as possible in order to differentiate their products from of government legislation and energy efficiency programs such the competition. as Energy Star, the European Ecodesign Directive and the China Standard Certification Center (CSC), there has been a major Probably the most progressive government for energy ef- focus on further driving down adaptors’ overall power con- ficiency standards is the State of California. Power supply sumption levels by minimizing the amount of energy used while manufacturers do not want to have specific models for Cali- in standby mode. The following article looks at the technology fornia only, so often the California standards have a very far trends emerging which are enabling the latest requirements to reaching impact. One example is the new Appliance Efficiency be addressed, including new processes that reduce the number Regulations outlined by the State of California in January of of external components this year, which focus utilized - leading to heavily on battery sleeker, more light- charger systems. With weight designs. around 170 million Standby power, chargers in opera- also sometimes called tion within the state, ‘vampire power’ or it is envisaged that ‘phantom load’, is the improving efficiency power consumed by levels in this particular electronic devices and area will save 2,200 appliances when they GWh of electricity an- are turned off but still nually. This is enough plugged in. It accounts electricity to power for approximately Figure 1: DOE’s proposed energy conservation standards for AC-DC external 350,000 homes - the 10% of the average equivalent of $306 mil- power supplies. US household’s total lion/year in residential/ energy usage. This commercial electricity equates to a stagger- bills. These regula- ing 129 TWh of power, tions, implemented by or the output of thirty the California Energy six 400 MW power Commission (CEC), stations - resulting in require compliance 75 million tons of CO2 from all the consumer emissions every year. chargers used by cell phones, personal care Figure 2: Typical old-style charging system for a power tool. In the US, the cur- devices and power rent federal standard, which went into effect in July 1, 2008, tools by February 2013, with industrial chargers needing to be requires that the no load power consumption of a power supply compliant in the following twelve months. Several other US under 250W be below 500mW. Recently, the US Department of states plan to follow the example set by California for reducing ® Energy (DOE) has proposed more stringent standards for the standby power limits. efficiency of battery chargers and electronic power supplies THiNK Keystone Solar Midget Fuse Holders ELECTRONICS CORP. to go into effect on July 1, 2013. Based on this standard, the Figure 2 describes the basic charger systems that were com- maximum power in no load mode must be less than 210mW for monplace in the past. In this particular example it is being used • Available in Surface Mount and Thru-Hole Mount • Specifically Designed It’s what’s on the inside that counts. a nameplate output power of 49 to 250W (a typical notebook to charge a power tool with a Nickel-Cadmium (NiCd) battery. for Photovoltaic (PV) Systems • Accommodates Midget (SPF) Fuse Series European Headquarters: adapter falls within this range). However, often these national The capacity of the battery over a 1 hour period is signified by (10 × 38mm) • Rated for up to 20 Amps • Fully Insulated • Low Profile 80, Rue Orfila, 75020 Paris, France energy regulations lag behind other standards and market C. For example, a battery rated at 600mAh could be charged at • Cost effective solution • Optional Cover available • Request Catalog M60 Fax: 33 (1) 46 36 81 57 • Tel: 33 (1) 46 36 82 49 0.5 C, resulting in a charge current of 300mA over two hours to e-mail: [email protected] • Web: www.keyelco.com Grant Floyd is product marketing engineer at fully charge the battery. ON Semiconductor - www.onsemi.com The circuit in figure 2 would be capable of delivering a con- 22 Electronic Engineering Times Europe May 2012 www.electronics-eetimes.com EETEuro-THiNKClouds+SPFH.indd 1 4/11/12 4:13:30 PM DESIGN & PRODUCTS POWER DESIGN stant charging rate of to a safe voltage level 0.1 C. As the charger’s within 1 second of un- 60 Hz transformer plugging the adapter was designed with the from the wall. If it does intention of keeping not, there is a risk of costs low rather than electrical shock from to allow high degrees touching the prongs of energy efficiency to of the AC plug. The be realized, the no load standard method for power would usually meeting this require- be over the 0.5W mark ment is to use a string - something that is no of high impedance longer deemed accept- bleed resistors in par- able. Early thinking was allel with the capacitor. to make the charger This constant resis- more efficient, without tive drain consumes paying attention to the approximately 25mW fact that after charging Figure 3: Simplified schematic of advanced charging circuit with no load of input power when the circuit would con- used in 230 VAC ap- detection. tinue to waste power plications. This 25mW indefinitely. This has becomes significant proved be a somewhat when considering misguided view. no load input power Even today many consumption. The chargers on the market NCP1246 addresses still lack the ability to this issue by includ- detect when the bat- ing an internal AC line tery is fully charged detector with active and as a result con- discharge circuitry. tinue to provide power The controller detects to the battery after when there is no the charging process longer an AC signal has been completed - present and activates thereby wasting energy an internal switch to (which is given off as discharge the capaci- heat). By employ- Figure 4: 65W adapter schematic. tor. With this feature, ing smarter charging the bleed resistors are systems capable of shutting down the electricity flow to fully no longer required, and the constant 25 mW drain is eliminated. charged batteries, energy is not needlessly squandered and the The secondary side SMPS controller (ON Semiconductor’s battery is not put at risk of being damaged. NCP4354) is a companion IC to NCP1246 and is capable of detecting no load conditions and entering the power supply into Innovative solution for low standby operation a low consumption OFF mode. During OFF mode, the primary One of the common contributors to standby power losses in side controller is deactivated and energy is provided by the the home is notebook adapters. These adapters spend much output capacitors. The output voltage of the adapter begins to of their lifetime underneath desks with the notebook computer drop as there is no more switching on the primary side. This is disconnected or powered off. A typical off the shelf notebook not an issue because the adapter is no longer connected to the adapter today consumes approximately 300mW to 500mW in notebook computer in this mode. The output voltage is allowed no load condition. However, many leading manufacturers are to decrease to an adjustable level before the NCP4354 signals now requesting that the no load power consumption of the next a primary restart to re-charge the output capacitors and thus generation notebook adapters be limited to less than 30mW in maintain operation. When the adapter is reconnected to the bat- order to differentiate their products from the competition. Figure tery, the NCP4354 controller automatically restarts the primary 3 shows a simplified example of a next generation charging side controller. Feedback control as well as ON/OFF signal can system for a 65W notebook adapter. The principal components be provided with only one opto-coupler. When used together in of this circuit are a fixed-frequency current-mode controller IC a circuit of this type, the NCP1246 and NCP4354 are capable of and a secondary side switched mode power supply (SMPS) achieving less than 10mW no load input power consumption on controller IC. US mains and less than 20mW on wide range AC mains. The fixed-frequency current-mode controller specified here Although many consumer electronics OEMs produce energy (the NCP1246 from ON Semiconductor) is specially optimized efficient products, they are often let down by inefficient charging to draw minimal power during no load and light load condi- systems. A great deal of progress has now been made so that tions. One of the major consumers of input power during no battery chargers can consume less energy while still offering load conditions in an AC-DC power supply is the X2 capaci- high performance benchmarks desired by the market.