Power Electronics

Can We Really Achieve Low Standby Power?

In a July 31, 2001 Executive Order, President George W. Bush started the ball rolling toward lower energy consumption in the United States. The Order states, “Each agency, when it purchases commercially available, off-the-shelf products that use external standby power devices, or that contain an internal standby power function, shall purchase products that use no more than one watt in their standby power consuming mode.” However, if products meeting this criterion were not available, agencies should purchase those with the lowest standby power. The Order also notes that Department of Energy, in consultation with the Department of Defense and General Services Administration, shall compile a list of products that meet the low standby power goal.

The Federal Energy Management Program (FEMP) developed guidelines specifying methods of measurement of electrical power consumption in the standby mode. They are applicable to mains-powered electrical devices. However, they are limited to devices where the consumer is expected to connect the device to the mains with a standard plug at a standard outlet. FEMP guidelines do not specify safety requirements or minimum performance requirements — nor do they set maximum limits on power or energy consumption.

The guidelines differentiate between the standby mode and the “sleep” mode or other reduced power modes that may be automatically initiated by the equipment under test (EUT): “The standby mode is generally different (and consumes less power than self-initiated modes). Certain devices are not equipped with power switches but employ sleep modes to reduce power use during periods of inactivity. For these devices, the standby and sleep modes are the same.”

What impact does the Executive Order have on the power electronics industry and the companies that supply components to it? For one thing, if a manufacturer does not sell to government agencies, there will be no impact. However, if an equipment manufacturer wants to sell to government agencies, an effort will have to be made to reduce standby power to an absolute minimum.

Because they have the most significant effect on power consumption, the semiconductor manufacturers will probably be affected most by the standby power edict. Reduction in power semiconductor losses will be necessary, which means lower on-resistance for power MOSFETs and lower on-state voltage drop for IGBTs. More of the newer ICs and power ICs will require a sleep or standby mode triggered by system inactivity. This is especially true for power supply and motor drive controllers.

The rest of the burden to lower power dissipation will fall on design engineers. They will need to configure the sleep mode in response to system activity. Designers will also have to emphasize power dissipation and efficiency.

From a design standpoint, there are problem areas that will be encountered. One example is a case where the normal operating is high, say 100A, and you put the system to sleep. How will the system react when power consumption goes from near zero to 100A? What effect will di/dt have on the system? And, how long is a user willing to wait for the system to go safely from zero to 100A?

If you have suggestions for minimizing standby power, send your comments to [email protected].

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