Making Smart Energy Even Smarter Via nanoPower Technology

April 25, 2017

David Andeen By: David Andeen
Applications Director, Core Products Group, Maxim Integrated


Several years ago, in 2011, we saw a lot of excitement around smart energy. For example, utility companies in North America were busy installing smart meters. In Brazil, Agencia Nacional de Energia Eletrica, the country’s electric power regulator, caused great excitement over its call for a full smart meter build out for the country. And in Europe, several utilities were creating their own unique ways to communicate from smart meters.

Creating additional buzz at the time, many companies were promoting home area network (HAN) solutions. There were exciting visions around including energy measurement devices on every washer, dryer, refrigerator…even light bulbs. Each device would conveniently communicate to the home router via ZigBee, Bluetooth, or another low-power, short-range communication protocol.

Flash forward to today and smart meters have been installed in most of North America and many countries in Europe and Asia. Utilities are monitoring power use. They’ve also saved some expenses by eliminating meter readers who would walk through neighborhoods to manually read each meter. However, the vision of a complete smart energy build out is different. We’re not really measuring, for example, energy on each light bulb, possibly due to the high cost of such systems versus the energy cost to run a lamp. Further driving down this energy cost are low-energy-consuming light sources like compact fluorescent bulbs and LEDs. Perhaps we’ve simply maximized our need for data at some levels of granularity. This, however, is not a situation that should cause despair. After all, while one vision of smart energy isn’t becoming reality, there are still many wonderful advancements that are supporting a new vision.

Take coffee, for instance. Ten years ago, it was common for most people and restaurants in North America to make coffee in a glass or ceramic pot that was then placed on a burner to keep it warm. Not only did that burner consume energy, but it also slowly cooked the coffee, ruining the taste. When someone had the great idea of putting coffee into a thermos to keep the heat of the coffee within itself, coffee drinkers rejoiced. This step took coffee “offline” as it was no longer connected to the power grid. As a result, coffee-making consumes less energy and results in a much better-tasting drink.  How’s that for a great example of smart energy?

The coffee example parallels other concepts for engineering systems that both maximize performance and save energy. One great advancement is nanoPower technology, where the current consumption of certain parts is in a quiescent state—not operating, yet also not completely shut down. Newer products, which take advantage of advanced analog CMOS process technology, operate with nanoamp currents that are so nominal they are almost immeasurable. These systems come with two major energy-saving benefits: first from duty-cycling them, and second, by decentralizing the power-consumption architecture. Next, let’s take a look at some examples of devices and circuits which provide the benefits of nanoPower technology.

Smoke detectors were among the first internet of things (IoT) devices. Typically, they’re expected to run for 10 years, on a battery, supporting infrequent battery changes and operation during power outages. Figure 1 shows a block diagram of a typical, modern smoke alarm featuring a battery, multiple DC/DC converters, a microcontroller, RF communication, a sensor (which may be a variety of architectures), and a piezo buzzer. In Table 1 are example values of current consumption for each block, based on modern components. In the case of optical smoke sensors, peak currents running LEDs will be in the mA range, but the average drops as the LEDs are typically cycled in at a relatively infrequent pace. In most alarms, the active circuitry may sample the air only 0.05% of the time. So for 99.95% of the time, the system runs in quiescent mode. Discounting the RF circuit, which may have a completely different duty cycle, the main circuits in full power mode would consume 11mA. During quiescent periods, the main circuit would consume 5.5µA. Therefore, the average current per second consumption by the active circuit is 11mA X 0.0005 = 5.5µA, which means that the average current consumption is 11µA. Note that any quiescent currents above one µA start to impact system battery life. So, in the 10µA current consumption range, each additional µA of current impacts a 1500mAhr battery life by a single year.    

Smoke detector block diagram

Figure 1.  Block diagram of a typical, modern smoke detector
 

Section

Typical Operational Current

Typical Quiescent Current

Microcontroller

10mA

2.5µA

Sensor

1mA

2.5µA

DC/DC*

3.5µA

500nA

*DC/DC power consumption based on an output current of 50mA with an efficiency of ~77%.

nanoPower technology also provides advantages via the ability to turn off circuits within the system. In this type of architecture, critical components like battery monitoring and real-time clocks stay on. Major power consumers, such as the microcontroller and RF circuits, either turn off or go into their lowest power consumption mode. The circuit in Figure 2 shows a nanoPower window comparator monitoring a battery voltage. The comparator provides a valuable safety function sending an alert only when the battery goes above or below the allowable voltages. The system microcontroller doesn’t have to operate unless it receives an alarm from the comparator, which runs at a typical current of 900nA. Essentially, this becomes a smart-energy architecture: it conserves as much energy as possible, while peeling off specific circuits for functions that have to stay on all the time.

nanoPower window comparator

Figure 2. nanoPower window comparator monitoring a battery voltage

A final example demonstrating the benefits of nanoPower technology is a power supply from a wall wart or battery, typically known as an ORing diode supply. In such supplies, good designers place a Schottky diode in series with the battery supply. This approach limits the voltage drop and, therefore, power loss across the diode, while still protecting the circuit. For example, the new MAX40200 ideal diode current switch drops as little as 85mV when carrying as much current as 1A, and typically drops 43mV when carrying 500mA. This performance is two to four times superior to the typical Schottky diode, smartly saving tens to hundreds of milliWatts of battery power.

Just like our coffee example, the smart-energy architecture is changing. Various sub-systems essentially disconnect from the central processor and check in periodically, which reduces energy consumption drastically. With advanced processing and analog architecture, these building blocks are now consuming unprecedented low amounts of power. However, the new smart-energy movement is about more than energy measurement and communication. The new smart energy comprises an intelligent system architecture combined with advanced components that together improve system battery life and reliability, unlocking new applications in the process.

Want to learn more about quiescent current? Read our white paper, Why Low Quiescent Current Matters for Longer Battery Life