Energy measurement circuit design using ADE7755 smart meter - consumer electronics circuit diagram

　　Energy measurement circuit analysis: ADE7755 is powered by a single power supply of +5V and power consumption of 15mV. After power-on, the ADE7755 chip is initialized and starts to work. The signals of the current channel and voltage channel are amplified by the amplifier and converted by the internal analog-to-digital converter. For two digital signals. When measuring power, the current path signal also needs to pass through a high-pass filter to remove the DC offset in the channel. At this time, the phase of the two channels may be inconsistent. For this, the phase angle change can be compensated through a phase adjustment circuit. Then the two signals are added to the digital multiplier at the same time, then pass through the low-pass filter, and finally enter the digital/frequency converter to obtain high-frequency pulses proportional to the instantaneous power and low-frequency pulses proportional to the average power, and respectively CF, F1, and F2 terminal outputs, the voltage signals sampled from the power grid are sent to V2P and V2N on channel 2, and then directly enter the digital-to-analog converter, and then enter the multiplier to provide power calculation. The two analog-to-digital converters in the chip Share a 2.5V reference power supply.

　　The electric energy measurement circuit is shown in the figure, which is mainly composed of a voltage detection circuit, a current detection circuit, an electric energy measurement chip ADE7755 and its peripheral circuits. First, the load current passes through the shunt and then through the filter circuit and is converted into a suitable voltage signal and sent to the current channel of the energy metering chip ADE7755, that is, the V1P and V1N terminals; while the 220V phase voltage is reduced through the precision resistor attenuation network and then passes through The filter circuit is fed into the voltage channel of the electric energy metering chip ADE7755, that is, the V2P and V2N terminals are converted into active power by the ADE7755 and output from the CF terminal in the form of high-frequency pulses and then connected to the external interrupt signal input terminal of the microcontroller AT89C52, which is controlled by the microcontroller. The circuit collects pulses from the CF terminal of the ADE7755 and sends the processed data to the LCD display circuit for display, and transmits the data to the host computer through the remote communication circuit. The CF pin is connected to the T0 counter of the microcontroller through the photocoupler. The microcontroller counts the pulses output by the CF pin, and then calculates the measured power according to the principle of ADE7755.

　　AT89C52 is a low-voltage, high-performance CMOS 8-bit microcontroller produced by Atmel Company of the United States. It contains 8KB of rewritable program memory and 256B of random access data memory (RAM). The device adopts Atmel's high-density, non-volatile Produced with volatile storage technology, it is compatible with the standard MCS-51 instruction system. It is equipped with a general-purpose 8-bit central processing unit (CPU) and Flash storage unit on-chip. The powerful AT89C52 microcontroller can be flexibly used in various control fields. The AT89C52 microcontroller is an enhanced version of the AT89C51 microcontroller and is compatible with Intel's 80C52 in terms of pin arrangement, hardware composition, operating characteristics and command system. AT89C52 is available in three packaging forms: PDIP, PQFP/TQFP and PLCC to meet the needs of different products. When the microcontroller operates normally, it requires a clock circuit and a reset circuit. The microcontroller reset and crystal oscillator circuit are shown in the figure.

　　AT89C52, clock circuit (including crystal oscillator, capacitor C19, C20), and power-on reset circuit (including R42, C5, S3, VD1, C3, R9) constitute the minimum system of the microcontroller. Among them, the crystal oscillator uses a 12MHz highly stable passive crystal oscillator, which forms an oscillator with the reverse amplifier in the AT89C52 to provide a highly stable clock signal to the CPU. Capacitors C19 and C20 can play a role in frequency fine-tuning. The capacitance value can be selected between 5pF and 30pF. For this circuit, 20pF is selected. Capacitor C5 and resistor R42 constitute a power-on reset circuit. When the power is turned on, the power charges the capacitor C5 and generates a high pulse at the reset terminal of the CPU. As long as the high level is maintained for longer than two machine cycles (24 oscillation cycles). The CPU can be reset. The function of the diode VD1 is to quickly release the charge stored in the capacitor C5 when the power is turned off, so that it can be reliably reset the next time the power is turned on. Capacitor C5 can filter out high-frequency interference and prevent the microcontroller from erroneously resetting. Button S3 and resistor R9 constitute a button reset circuit.