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  • MCP3901 Low-Cost Power Monitor

  • Created: May 16, 2016

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Summary

This reference design is a low-cost power monitor using MCP3901 from Microchip Technology. This MCP3901 is a dual analog-to-digital converter (ADC) that is used to acquire current and voltage samples. Furthermore, this design is used to evaluate the functionality and performance of the MCP3901, as well as a development platform for PIC18F-based applications. A programmed PIC18F25K20 device in the power monitor processes samples acquired by the MCP3901 to obtain Root Mean Square Voltage (URMS), Root Mean Square Current (IRMS), active power, apparent power, and power factor values.


There are two voltages required for the power monitor to operate. A 3.3V is used to power the microcontroller, while a 5V is used to power the ADC. For this reason, two MCP1703 Low Dropout Voltage Regulators (LDOs) are placed after the C51 capacitor, with the required voltages at the outputs. The meter is powered from the capacitive divider composed of C6 and R53. A parametric regulator circuit, using Zener diode D5, limits the input voltage of the LDOs to 12V. The rectifier diode D2 restricts the current flow to a single direction, while ripple is reduced by C51 and the LDOs. Using the external ADC, the current and voltage samples must be acquired before the correct values of the desired parameters can be computed. The MCU reads the values of the samples from the ADC through the SPI bus. On the other hand, a PIC18F25K20 MCU is used in this design. An LCD is also used to display the measured voltage, current, and power. Since the MCU does not include an LCD driver, the LCD used in this reference design has the built in driver. The connection between the LCD and the MCU carries four lines of data and three lines of control.


This design is useful in industrial applications as an energy measurement device. Since it has also a power factor correction feature, it can be a great help in industries. Other applications of this design also include smart plugs, smart appliances, and others that require utility metering.

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