Did a teardown of a 16A Smart Plug from Wipro. It is a WiFi Controlled switch with energy monitoring.
it was quite interesting to see a power switch with energy metering inbuilt and how they packaged everything in such a small space.
It wasn’t so easy to open, you need to use screw driver to open it by pressing the ON/OFF button on the sides.
The architecture is almost similar to what you might have seen in any other Smart Switch. An AC to DC converter for powering the circuit, relay as a Switch, WiFi module or Wireless SoC and Energy Metering chip in case of this Smart Plug.
In this design, at the input first MOV is sed for high voltage protection, then a basic pie type line filter and then AC to DC Conversion is done using OB222MCP
In a few designs where power consumption is very low a capacitor drop based method could be used for AC to DC conversion but here as a relay is required to be powered along with Wi-Fi and other circuitry, a AC to DC is converter using a power conversion IC.
After AC input is converted to 5V DC it is again converted to 3.3V using linear regulator onboard, A1117B 3.3.
Main MCU for the design is CB2S module from Tuya.
Relay used is from Yuanzi Electric YTA-SS-105DM 250V AC 16A
For Energy measurement, they have used single chip energy metering IC from BL0937
Circuit will be something like this:
Looking at the power traces, I am not confident that it will work with 16A load continuously. We will definitely have heating issue and switching section of the Smart plug may get damaged.
I am also not sure, how much accuracy is possible using BL0937B energy metering chip as it is giving data in the form of pulses. MCU need to count these pulses to derive the energy getting used.
I hope you found this teardown useful and learned something new today!
If you have any questions please ask in the comments section below, I will try to respond as soon as possible.
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I am currently working as an embedded systems design consultant and helping companies build custom embedded products, develop test automation solution for their PCB or complete product.
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