Reduce standby mode energy use

The number of electrical products used in private homes and offices is growing at an extremely fast pace. The problem with most of these products, such as A/V products and office equipment, is that they consume considerable amounts of electrical power during standby. This is a waste of electrical power and money, and has a negative impact on the environment. That is why today, for a large number of products, there are regulations that fix stringent limits for standby energy consumption. This article proposes a power management solution for electrical devices during standby mode, compliant with power efficiency specifications.

Besides intelligent power management, an advantage of the proposed system architecture is its general purpose usage independent of the product. It can be easily adapted and embedded in consumer devices, office equipment and home appliances.

Normal standby

Standby mode refers to a product's state when it is switched off but still connected to the main power supply. Active mode refers to a product's state when it is switched on and running normal functions. Because many devices stay in standby mode most of the time -- a DTV or a printer, for example -- an energy cutback during this phase would determine an overall energy savings.

Current specifications from Energy Star require standby power consumption be less than or equal to 1 - 2W, depending on the type of equipment. For A/V products this value is fixed at 1W.

Power management solution

ST proposes a smart power management control, necessary to design systems with sustainable principles. This is done by adding a general purpose low-power MCU to the main system that has specific firmware responsible for power control.

The figure below shows the block diagram of a generic system that could be of an A/V product, office equipment, or home appliance product. Independent from the application, we can distinguish two parts -- the main system block and the power management block.

General system block diagram Click on image to enlarge.

The main system block performs the primary function of the system; its hardware topology is different for different products, but each one has a main IC controller with an I2C bus and at least one wake-up source.

The main IC controller manages each system function, interfacing with a standby controller, wake-up sources and the other devices. Wake-up sources are events that can command the standby controller to exit the standby mode and return to the active mode. Common wake-up sources are a remote control receiver, a keyboard, VGA and HDMI inputs. A wake-up source could be also a timer event, used to record, start a special operation or for periodic update.