Don’t Forget About Standby Power: Page 3 of 3

Standby power management technology has enabled the resource constrained IoT world but not without trials.

Power Management Technology

A power-management system controls, regulates, and distributes power in an electronic system. Power management technology was first implemented in PCs back in 1989, when Intel developed processors that could be slowed down, suspended and even selectively turn off power to different parts of the system platform (e.g., like the hard drive) to reduce energy consumption and increase battery life.

Today’s embedded and IoT devices have built upon the power management approaches of the past. To make power design and control more practical, designers have separated the power domain into three power subsystems or sectors: microcontroller, RF and wireless transceivers, and sensors and actuators. These sectors, sometimes known as power islands, align with the typical operational use case of an embedded or IoT device, where data is acquired by sensors, sent or received via wired or wireless connectivity, and used to control mechanical devices like actuators.

Regardless of the subsystems, both hardware design and software techniques are needed to make efficient use of battery storage and wall-output power sources. Hardware design includes the careful selection of processor, memory, interface and passives components to optimize power consumption during operation but also at rest. Software power management techniques include switching off peripherals when they are not in use and adjusting the frequency and voltage of the CPU according to the required performance requirements. This is often known as Dynamic Voltage and Frequency Scaling or DVFS.

Another technique is power gating, which is used to lessen the power leakage of smaller chip process nodes. Power gating works by turning off the supply voltage of unused circuits. It does incur an energy overhead; therefore, unused circuits need to remain idle long enough to compensate for this overhead.

In a chip or printed circuit board, the processor controls most power management actions via software. For example, most modern processors support three levels of sleep to conserve power:

  • No sleep – The device is always-on, always consuming power.
  • Light sleep – In this mode, the processor is often suspended, and its internal clock is turned off.
  • Deep-sleep – In this state, everything is turned off except the RTC (Real Time Clock), which enables the clock to be turned on periodically. This is the most efficient mode. It is used when the device needs to send data at specific intervals, e.g., to read sensor data, transmit it and then go back into a deep-sleep mode.

Moving on to the RF and wireless transceivers power subsystems, low-power wireless technology options like Bluetooth, Zigbee and Wi-Fi must be balanced with performance needs, battery life and data throughputs. Such an evaluation is heavily based on the application and will be covered in another article. Its sufficient to note that, like the processor, RF and wireless subsystems can also be placed in standby mode to conserve energy.

Standby power techniques can also be applied to sensors and actuators. IoT sensors typically spend significant amounts of time in sleep mode, so idling the device for low sleep power is an obvious technique. Naturally, energy consumption of sensing devices varies widely with the requirements of the application. Often it is best to consider the standby power needs of the entire system. For example, smart sensors are capable of performing basic computations, thus removing some of the compute (and power) loads from the main system processor.

A systems approach to standby power management – and power management in general – will permit a balanced consideration of all power needs plus the timing of those needs. An understanding of the overall power requirements will enable a partitioning of power resources matched with the appropriate implementation technologies to ensure the entire system will operate as desired.

Image Source: Photo by Thomas Jensen on Unsplash

John Blyler is a Design News senior editor, covering the electronics and advanced manufacturing spaces. With a BS in Engineering Physics and an MS in Electrical Engineering, he has years of hardware-software-network systems experience as an editor and engineer within the advanced manufacturing, IoT and semiconductor industries. John has co-authored books related to system engineering and electronics for IEEE, Wiley, and Elsevier. 

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