Standby
[edit] Standby Power
Standby power is a product's minimum power consumption while plugged in and not performing its primary function (sometimes called the "off mode" consumption) or while at its lowest power mode. For appliances with a power switch, we measure the power draw while the unit is "off". For appliances without a power switch, such as cordless telephones, answering machines, and battery chargers, power draw is measured while the units are plugged in, but are not being used by the consumer. A few appliances are much more difficult to measure. Refrigerators, for example, have hidden functions that can be difficult or impossible to turn off. Since some of these hidden functions are not considered "standby power", it is nearly impossible to get an accurate measurement.
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When appliances are off, they usually consume power at very low levels of between 1 and 10 watts. Few meters have sufficient resolution to measure standby power accurately. These cost over $500. A few meters are now available for less than $100. Unfortunately their accuracy below a few watts is poor. These are nevertheless indicative of standby power. You can improve accuracy by adding a standard load (such as an incandescent light bulb) into the circuit; then measure the difference in power consumption.
To start measuring your standby power usage, start by visiting this page from Lawrence Berkeley National Laboratory. Or look at a chart on average, minimum and maximum standby power consumption of various appliances is availabele here. A more comprehensive listing is found at this US Department of Energy webpage
Standby power use is roughly responsible for 1% of global CO2 emissions(Meier, 2000). Reduction can only result from both improved technologies and heightened consumer awareness. Programs directed at consumer electronics have stimulated manufacturers to cut standby power use in many products. Standby losses are expected to grow as traditionally electromechanical appliances become digital and home electronics become more widespread worldwide. Moreover, the coming age of interconnected appliances may increase standby power usage, but it will be justified, since it will provide benefits to consumers.
A large portion of standby losses can be attributed solely to low-voltage power supplies. Standby losses are also commonly caused by components that give an appliance the capability to be powered remotely, display information, maintain an internal clock or memory, or charge batteries in standby mode (Huber 1997). Such features may require some components to continuously consume power. Frequently, however, components that do not need power in standby mode are powered unnecessarily.
When an appliance is in standby mode, power losses occur whenever current flows from the source through the power supply, usually to provide power for standby functions performed by the circuitry and I/O components. If the appliance needs power in standby mode, therefore, at least the power supply must be active. This nearly always generates some losses (and account for most of the losses in the standby system), the magnitude of which depends on the efficiency of the power supply. For each additional component that receives power, more losses accrue. Ultimately, the whole is equal to the sum of its parts; i.e. the appliance's standby loss is equal to the sum of its components' losses.
[edit] Power Supply
Power supplies convert ac power from a wall outlet into lower voltage dc or ac power to be used directly by electronic circuits. EPA’s research has indicated that approximately one-third to one-half of the electricity that flows through power supplies is consumed in the power supply itself, as these power supplies are only about 50% to 70% efficient.
- Switching to "Switching" Power supplies. The two main types of power supplies used today are linear power supplies and the more efficient electronic "switching" power supplies. Changing from linear to switching power supplies would not only reduce standby losses, but would also improve efficiency when the appliance is on (Meier & Huber 1997). For situations in which a switching power supply cannot be used, linear power supply efficiencies can be improved by using more metal, and more and thinner laminations in the core of the transformer (Rainer, Greenberg & Meier 1996).
- A second power supply specifically for lower power standby mode. This is a common practice.
- Turn the power supply off when the appliance is off. A simple way to do this is to design the appliance so that the power switch is on the high-voltage side of the power supply. Other possibilities include designing a smart power supply that can sense when the appliance has been turned off, or offering an optional standby mode by using a power supply with a three-way on-ready-off switch — a feature offered on most non-US television sets. If an appliance needs just a few milliwatts of power in standby mode, rechargeable batteries can be used to provide power to components that need it. As photovoltaic and energy storage technologies improve, it may even become cost-effective to keep components or batteries charged with small photovoltaic cells.more explanation needed
[edit] Circuitry
After the power supply, the next destination from an electron's perspective is the internal circuitry. Depending on the appliance, the circuitry almost certainly contains one or more oscillators and some kind of control circuitry, the combination of which allows the appliance to perform functions pre-programmed by the manufacturer or requested by the user. More complex circuitry may also contain memory where information such as consumer preferences can be stored. Power management technologies have the capability to reduce the standby power consumption of any circuitry to less than one microwatt (EPC 1998).
- Oscillators. When an appliance is in standby mode, oscillators continue vibrating for standby components to be active. Higher efficiencies can be obtained by switching to a lower frequency oscillator. Lower-frequency oscillators are commonly used to conserve energy in battery-powered applications.
- Control Circuitry. Most home appliances have very simple control circuitry, consisting of a single micro-controller chip and its firmware. A computer uses a much more complex system of circuitry and integrated circuit (IC) chips. Consumption depends on the complexity. However, because portions of circuitry, and even portions of chips, can be shut down while other portions remain powered, even the most complex circuitry needs a very small amount of power to respond when needed.
- Memory. There are a several different types of memory commonly used in electronic devices. The most common memory storage device is the register, which is composed of just a few transistors, each requiring only microwatts of continuous power to retain information. This tiny amount of power is often supplied by a battery or supercapacitor to protect against power failure. There is also non-volatile memory that uses no power to retain information. Memory technologies such as non-volatile ferroelectric RAM (FeRAM) provides unlimited read/writes, high speed operation, and low power.
[edit] Input/Output
The input/output or "I/O" system consists of emitters and receptors that allow an appliance to communicate with the user and other electronic devices and also to monitor itself and its environment.
- Emitters. An emitter is any device that sends out light or some other type of signal, such as time, status, or button illumination. The most common luminescent displays are light emitting diodes (LEDs) and vacuum fluorescent displays (VFDs). A commonly used non-luminescent display is the liquid crystal display (LCD) which is typically black and white. In some applications, such as portable computers, LCDs are enhanced with color and background lighting. A simple standby light consisting of a single LED, consumes only about one-twentieth of a watt. A full four-digit clock display, on the other hand, requires about 30 LEDs and about 30 times as much power. Newer display technologies accomplish the same goals, with significantly less energy.
- Receivers. Receivers are devices that sense an incoming signal and relay the message to components that can interpret and/or react to the message. Receivers are regularly on at all times so that appliances in standby mode can respond to external conditions or signals. The most common receivers are radio or infrared sensors for reception of remote control signals. Some other common receivers include temperature sensors, motion detectors, and analog and digital signal detection devices.
