AC power monitoring is an amazing feature nowadays in IoT related applications, such as smart fans, switches and boards. Some good company boards implement this tech in their products and continuously monitor the supplied output power. Monitoring power at local device level has its own advantages, like now we have data, if current increases and something goes wrong it can turn off the whole system and can save equipment from burning. Moreover power monitoring in IoT uses ASIC based designs, I got myself one let’s explore the working. This article is sponsored by PCBWAY, they provide a full proof prototyping solution from manufacturing PCBs to CNC. PCBWAY is popular because of its reliable services over the time in the electronics industry. Sign-up now using the link and get free coupons for your first PCB order.

BL0937 and Power Monitoring:

The IC from Shanghai Belling, BL0937B is a wide range of single-phase multi-function energy meter IC for single-phase socket, Smart Appliance, with a low cost and high accuracy. BL0937B integrates two high-accuracy Sigma-Delta ADC, voltage reference, power management and other analog circuit modules, and digital signal processing circuit to calculate active power, IRMS, VRMS etc.

Features:

• High accuracy, less than ±0.5% error over a dynamic range of 2500: 1
• High stability of large signal, in the condition of signal 300mA, less than ± 0.2% error in the output frequency fluctuation (CF).
• High stability of small signal, in the condition of signal 50mA, less than ± 0.3% error in the output frequency fluctuation (CF).
• Current and voltage RMS, current measurement range (8mA ~ 30A) @ 1mohm
• On-Chip anti-creep protection
• On-Chip power supply detector
• On-Chip voltage reference of 1.1V(typical)
• On-chip oscillator as clock source
• Single 3.3V supply, low power (8 mW typical)

Measurements of Voltage, Current and Power:

The IC has one input control pin, named as SEL(select), Two output pins (CF and CF1).

High frequency CF1 is provided for indicating IRMS/VRMS and high frequency CF for energy metering. BL0937B can measure the single-phase active energy, active power, current and voltage RMS and other parameters to fully meet the needs of the socket, power strip, smart appliances and others. Interrelated patents are pending.

IP and IN: These inputs are fully differential voltage inputs with a maximum signal range of ±50 mV. Because of the internal ESD protection circuit, If the voltage exceeds ± 1.5V the IC will not be damaged badly.

VP: Positive Input for Voltage Channel. The Voltage Inputs are differential voltage inputs with a maximum signal range of ±200 mV. Because of the internal ESD protection circuit, If the voltage exceeds ± 1.5V the IC will not be damaged badly.

CF: High frequency pulse output for active power, the pulse width is fixed to 38uS; the frequency is proportional to the active power value. Over-current indication pin; If overcurrent occurs, the pin outputs a 6.78KHz pulse.

CF1: When SEL=0, the output is current RMS, pulse width is fixed to 38uS, The frequency is proportional to the current RMS value. When SEL=1, the output is voltage RMS, pulse width is fixed to 38uS, The frequency is proportional to the voltage RMS value.

BL0937B measures two voltage signals on current channel and voltage channel and then calculates the real power information. This real power information is then converted to a frequency. The frequency information is output on CF in the form of active high pulses. At the same time current RMS and voltage RMS are calculated and converted to a frequency, and output on CF1 in the form of active high pulses.

Circuit Diagram:

Typical Application BL0937B Typical application block diagram is shown below. Single 3.3V supply. The current signal is sampled through the alloy resistor connected to the IP and IN pins of BL0937B. The voltage signal is sampled through the resistor divider network connected...