Brief Introduction of Power Line Carrier Communication IC-LM1893 and Application Circuit-EEWORLD

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Power line carrier communication uses existing power lines to transmit signals. Its working principle can be briefly described as follows: data or voice is modulated on a carrier frequency of tens to hundreds of kHz and sent out through the power line. The receiving end receives the carrier carrying the signal on the power line and demodulates it to restore the original voice or data. The carrier of communication is the existing power line, so there is no need to re-lay the communication line like wired communication. It does not require complex sending and receiving equipment to transmit information like wireless transmission. It does not require additional communication lines and does not occupy precious wireless spectrum resources. Therefore, it is very suitable for forming a local area network within a small group (generally between the same power transformers) to achieve the purpose of data or voice transmission.

LM1893 is a power line carrier communication integrated circuit developed by National Semiconductor. It integrates all the functions of sending and receiving data and can realize half-duplex communication of serial data. Only a small number of external components are needed to form a complete power line carrier communication system, which is suitable for industrial automatic control systems, building data or voice communication, centralized control of household appliances, emergency call systems in hospitals, fire alarms and computer data transmission. Its main features are as follows:

FSK anti-noise modulation technology

Pulse generator with selectable noise filtering

Data transfer rate up to 4.8kB

Sine wave carrier frequency to reduce RF interference

RF power can be increased 10 times

The carrier frequency can be selected between 50-300kHz

Compatible with TTL and MOS logic levels

Adjustable voltage to power level

Can drive various existing power lines

Working Principle of LM1893LM1893
integrates two independent parts, transmission and reception. The transmission part has built-in FSK modulator, sine wave generator, current-controlled oscillator, automatic gain control circuit (ALC) and output power amplifier and other unit circuits. The receiving part includes limiting amplifier, phase-locked loop demodulator, low-pass filter, DC clamping circuit and noise filter and other unit circuits. TX/RX is the control pin for transmission or reception. When TX/RX is high, the circuit is in the transmission working mode. The data signal is input from P17 to the FSK modulator, forming a switch control current and driving the oscillator to generate a triangle wave with a frequency deviation of ±2.2%. The sine wave shaping circuit outputs a sine wave signal, which is then transmitted to the power line by the coupling coil after power amplification. ALC (automatic gain control circuit) ensures that the output carrier level remains within a certain level range when the load of the power line changes.

When TX/RX is at a low level, the circuit is in receiving mode. The signal on the power line is input through the coupling transformer: LM1893's 10th pin, and enters the limiting amplifier for amplification. The DC component and 50Hz/100Hz industrial frequency signal in the signal are filtered out, and then the phase-locked loop circuit demodulates and the RC filter circuit filters out the high-frequency component to output the data signal. In order to keep the data signal reliable, it is shaped by the comparator and filtered by the noise filter, and finally the complete data signal is output from pin 12.

Reference address：Brief Introduction of Power Line Carrier Communication IC-LM1893 and Application Circuit

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