Power Tips: Powering the IoT in Our Homes

Other Parts Discussed in Post: UCC28710, UCC28910

The internet of things (IoT) is already here. There has been a lot of buzz lately about the IoT and speculation about how it will shape our lives in the near future. Learn the uniqu requirements of your power supply with these connected devices.

The Internet of Things (IoT) is already here.  There is a lot of buzz lately about the IoT and speculation about how it will shape our lives in the near future.  While we have much further to go, look around your home and you will realize that we began this journey years ago. 

In order to understand how the IoT has already impacted your life, you must first get a general idea of what the IoT refers to.  What is the IoT?  It is basically the trend of devices and appliances (“things”) connecting to the internet to allow additional functionality such as control, transfer of data, etc.  For a more detailed description of the IoT, read about it here.

What examples of IoT connected devices can you find in your home? 

One of the more obvious “things” that has joined the IoT, is our home thermostats, fire alarms, and carbon monoxide detectors.  The Nest smart thermostat has been widely popular and has sparked many similar competing products. 

On the outside wall of your home is another example.  Smart power meters have been deployed by the utility companies for many years.  This saves money by eliminating the need for a human to travel around reading meters, and collects valuable information about energy usage over time.

With a trip to your local home improvement store you could buy products that allow you to connect much more of your home to the IoT.  Smart outlets, light bulbs, and light switches are available now that allow home owners to track and control their energy usage room-by-room, or outlet-by-outlet.

Although some IoT devices are becoming common place, 4 less expected IoT devices in your home are smart meters, wall outlets, light bulbs and light switches. All require AC power.

So what does all of this have to do with switching power supplies?  All of our examples already have power available to them, but it is AC.  To power controls, sensors and microprocessors, we need a low-voltage, low-current AC/DC supply.  These supplies usually do not require safety isolation, as they are not typically user-accessible.  The supplies must be small; after all, nobody wants a giant power supply to power a tiny microprocessor circuit. So here are 11 PowerLab reference designs for AC/DC IoT devices in your home!

11PowerLab reference designs for AC/DC powered IoT devices.

When safety isolation is not required, low-power flyback supplies can offer a very small, efficient and cost-effective solution.  This is a good solution for applications that require functional isolation for sensing the AC  line current, e.g. power meters and smart outlets.  Here are some PowerLab examples of flyback supplies for powering home devices in the IoT:

 3 low-power flyback power supplies for when safety isolation is not required.

  • PMP8968 – 230VAC Input, 5.5V/250mA Flyback Converter
  • PMP9059 – 120VAC Input, 5V/200mA Flyback Converter With BJT Switch
  • PMP9235 – 120VAC Input, 5V/250mA Flyback Converter With BJT Switch

For applications only in the North American market (120VAC), a SEPIC converter can also provide a compact solution:

4 compact SEPIC converter power supplies for applications in North America

  • PMP5298 – SEPIC (5V@250mA) for Auxiliary Bias Supply
  • PMP5353 – SEPIC and LDO (3.3V@40mA; 15V@2mA)
  • PMP5422 – SEPIC (5V@250mA) for Auxiliary Bias Supply
  • PMP6711 – 120VAC Input to 5V/1.25W Output, Ultra Compact Isolated SEPIC

It is also possible to create a high-voltage buck supply:

  • PMP9087 – Universal AC-DC Buck converter using UCC28710
  • PMP9176 – Ultra Wide Input Voltage Range AC-DC Buck Converter using UCC28910

Another option traditionally used in power meters is the cap-drop method.  This method feeds a low-voltage linear regulator or buck power supply through a series-connected capacitor.  The impedance of the capacitor at the line frequency limits the input current.  A minimum load current or zener clamp limits the voltage feeding the linear or switcher.  A major drawback for this approach is the fact that the required AC blocking capacitor can become physically large, especially for applications with a wide input range or slightly higher power levels.  Here are some examples of cap-drop supplies:

2 cap-drop power supplies for power meters

  • PMP9310 – 3.3V Low-Cost Non-Isolated Offline Converter for Smart E-Meters
  • PMP9311 – Cap-Drop Offline Power Supply for Standard-Compliant Feature-Rich E-Meters

While the IoT has already started to improve our lives at home, it will affect us in many more ways in the near future.  Our automobiles, retail and grocery stores, and work places are all becoming connected now.  What other areas of your life has the IoT touched?

Find all PowerLab Notes here.