Power is the most quintessential requirement for your IoT device. Without power, and without power being managed and distributed properly, your device can either not work or give someone a very nasty shock. In this article, I will talk about what a power converter is, ideal power sources for IoT devices, how to design one, and how you can easily measure and reduce your device’s power consumption.
But What Is Power?
Any IoT device will need electricity to work. Whether coming from a power outlet or a battery, your device will always require a certain amount of voltage and current. The product of those two (voltage and current) is called power. The amount of power that is being consumed in some time period is the device’s energy. It is important to understand these two terms since we will refer to them a lot for the rest of the article.
Most often, the power that your device requires will be very different from the one that is readily available. A typical IoT sensor will usually require either 5 volts or 3.3 volts and anywhere between 30 mA to 1 A. On the other hand, the power supply from your outlet can vary from anywhere between 110V (e.g. USA) to 240V (e.g. India). As you can probably imagine, connecting your mains supply directly to this sensor will not only destroy your device; it could also potentially cause fires and hurt someone. This is why we use power converters that can reduce the voltage level such that it can be safely connected to the sensor.
So What Is a Power Converter?
The best example of such a device is your mobile phone charger. I think it’s very surprising how little people think about the charger they use every day. It’s actually an amazing device it actually is. It can convert an extremely high voltage of up to 240 V and potentially even 16A to a harmless 5V and 2A. Moreover, it does not matter whether the input is 110V at 60Hz or 240V at 50Hz, it will still give the same 5V and 2A output without breaking a sweat. On the other hand, there are also a lot of cheap or fake chargers that are available that can stop working or even shock or burn you. The difference between good and bad power converters is a set of rules and regulations that are followed and tests that are conducted to make sure that your device is not only safe to use but can also endure.
It isn’t necessary for a power converter just to be able to convert power from a high voltage to a lower voltage. In fact, anything that converts power from one type of frequency, voltage, or voltage shape to another type of frequency, voltage, or current can be a power converter. However, the most common ones for IoT devices are the ones that convert a high alternating voltage to a low fixed DC voltage.
To summarize, our power supplier should be able to convert a high voltage, high current, and highly fluctuating power supply into a stable supply equivalent to what our device needs to work properly and safely at the same time.
Security and Safety
“Stability” and “safety” are very vague terms for someone who has to design a product that fits those criteria. Let’s dig deeper and try to iron out those terms in clear terms.
5 Elements of Good Power Supply Design
1: Under Voltage Cut-off
Like all devices, even our power converters have a range of voltages and currents within which they operate. As a designer, you can try to make this range as large as possible, but eventually, you will hit a cost/profit wall. As such, your power converter should know when the voltage that is being given to it is too low for it to convert to the required output properly and cut off the output to prevent damage to the rest of the circuit. This is especially important when you are using it to charge a battery and a low voltage can damage the battery.
2: Over Current Protection
A short-circuit in either your device or your power converter could cause a sudden spike in the current output of your converter. In these scenarios, your converter should open the circuit to prevent any damage to the device and the user.
3: Surge Protection
No power utility is perfect. There might be a few cases in which the input to your converter will have a high current or voltage. While these “surges” are usually short-lived, they can still harm your batteries and your device. They should be dealt with gracefully. The best way to do so is to ground your devices. And voilà, our fourth point:
Grounding is very important in all modern day devices. If something goes really wrong in your device—e.g. a short-circuit or a loose wire shorting the case of your device—grounding is usually the last line of defense against a potentially deadly accident. In simple terms, grounding reroutes stray and excess charges from your device back into the ‘Earth’.
5: Stability and Isolation
The mains power is highly fluctuating (50Hz to 60Hz). Converting that to a stable 5V output supply can be very hard—and dangerous if done incorrectly. One of the best ways to achieve a good result is to use SMPS (Switch Mode Power Supply) circuits. These circuits convert power by switching ON and OFF in very high frequencies.
Isolation is also important. Since the adapters tend to be very small, it’s easy for a high voltage line to get shorted with a low voltage one, which can be deadly if someone touches the seemingly harmless 5V output part. Isolation tries to minimize that from happening by not having
What Can Happen If The Power Is Irregular?
Lots of nasty things can occur. At worst, a short circuit in the converter could expose your device and user to the mains voltage which can be deadly. This is where proper grounding can help minimize some of the risks by diverting the excess power away from the device.
However, even a minor failure could result in an erratic supply for your IoT device. And even though a few volts here and there might not harm your users, irregularity can cause your device to malfunction and reduce its longevity.
What Next for IoT Power Supply Design?
Designing a robust and resilient IoT power supply is no easy task. IoT devices can be prone to failure. The best way to go about designing a new converter would be to look at how some of the best people in the industry are doing it. Apple has spent years researching and designing their converters. They go above and beyond when it comes to safety. Here is a nice teardown article of an iPhone charger that explains in detail the various components of the charger and what each component does. And here is an article about the harmful effects of not having a good power converter.