Cut standby drain to increase energy efficiency

Article By : Akshat Jain, Ranajay Mallik

A typical household appliance consumes standby power in the 0.5W to 5W range. Reducing that unwanted energy consumption can help save a lot of power.

Most electrical and electronic appliances draw power 24×7 even when they are not performing their primary function. This standby power is consumed by power supplies that run the circuits and sensors needed to receive a remote signal, soft keypads, switches and displays including miscellaneous LED status lights. For example, a 32-inch LED TV under normal use consumes 50W but still ~1W in standby mode. Imagine a million TV sets in standby for a month<img alt="

A typical household appliance consumes standby power approximately in the range of 0.5W to 5W, but a home or office has many appliances, which all together amount to a significant amount of electrical waste. It is estimated that the standby power is responsible for producing 1% of global CO₂ emissions. Therefore, reducing unwanted energy consumption associated with standby power can help in saving large amount of power and reducing risk of global warming.

Industry standards

Various agencies following different international standards with common aim of reducing standby power consumption.

– IEC 62301
IEC 62301 specifies methods of measurement of electrical power consumption in standby mode for “energy labelling”. It is applicable to electrical products with a rated voltage that lies wholly or partly in the range 100V A.C. to 250V A.C. for single phase products. IEC 62301 Clause 4.5 states that the power supply of the appliances consuming less than 5mW during standby mode can be rounded down to zero or can be termed as “Zero Standby” power consumption.

– Energy Star
Energy Star is an international standard for energy efficient consumer products sold in the United States. It was created in 1992 by the U.S. Environmental Protection Agency and their Department of Energy. Since then, many countries have adopted the programme. Energy Star qualified electronics must consume no more than 1W in standby mode.

– Bureau Of Energy Efficiency
The Bureau of Energy Efficiency is an agency of the Government of India under the Ministry of Power. It was created in March 2002 under the provisions of the 2001 Energy Conservation Act. The BEE has different ratings for various appliances and BEE qualified electronics must follow norms as per 3.6 clause of IEC 62301. For example, the standby power consumption for a TV with LED backlight should be <0.6W.

– The Blue Angel
The Blue Angel (Der Blaue Engel) is a German certification for products and services that have environmentally friendly aspects. The Blue Angel qualified electronics must consume no more than one watt in standby mode.

Some of the strategies used to reduce standby power consumption and total energy of electrical appliances are:

  • Efficient Power Supply – Exploring new topologies, advanced components and by tweaking configuration, designers are making power supply itself more efficient.

  • Extending smartness to the electronic devices or appliances:

    • Sensors and actuators are made to integrate with electronic devices to analyze and take decision autonomously.
    • Electronic devices are made to connect with network using wireless protocols such as Bluetooth, Wi-Fi, 4G etc. to have better control and monitoring.
    • Curb idle time – Many appliances such as computers and video game consoles come with an option to configure sleep mode and powering down time interval.
  • Upgrading Semiconductor processes – Semiconductor companies are coming up with newer fabrication processes to meet energy-saving standards with respect to low-power modes.

A typical appliance

Let's take a look at how this standby power flows in a general block diagram representing a typical electrical appliance (see Figure 1). The blocks circled by the red dotted line need to stay active to ensure user responses and commands are not missed by the appliance even when it is off.

[Low StandBy Power Jain Mallik ST Figure1 (cr)]
Figure 1: The general block diagram of an electrical appliance.

The total power consumption is that of the actual load plus the consumption due to this active stage. Modern appliances keep this stage active and shut down the main power consuming block when not in use. This means the standby consumption is entirely dependent on the blocks inside the red dotted line: the auxiliary power supply and the user interface.

If we can design this stage to consume minimal power, we can meet the standby consumption requirement laid out in any geographic region. So, let us look at an example where the system consumes <50mW in standby.

We will develop a system that will evaluate a particular feature of STMicroelectronics' VIPer0P device: the zero power mode (ZPM). The system mainly comprises:

  • VIPer0P – Zero-power off-line high voltage converter
  • STM32L052K6 – Ultra-low-power ARM Cortex-M0+ microcontroller

The VIPer0P is a standard fixed frequency monolithic flyback converter that can handle up to 7W but with some added stages for achieving zero power during standby (see figure 2). The zero-power mode (ZPM) feature enables VIPer0P to work in an idle state, where the system is totally shutdown with no switching activity.

[LowStandByPower Jain Mallik ST Figure2 cr]
Figure 2: The VIPer0P block diagram.

Next: Getting standby power below 50mW »

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