Patent ID: 7813368
Filing Date: 2010-10-12
Classification: G08C

Abstract:
1. A communication system, comprising: first and second communication wires; a local device having positive and negative terminals; a slave controller connected to the first and second communication wires and connected to the positive and negative terminals of the local device, the slave controller being fed with a first direct current voltage via the first and second communication wires and feeding a second direct current voltage to the local device; and a master controller connected to the first and second communication wires, the master controller having a feeding phase for feeding the first direct current voltage to the first and second communication wires and a communication phase for communicating with the slave controller by changing the first direct current voltage in such a manner that voltages on the first and second communication wires are opposite in phase, wherein when the master controller communicates with the slave controller, the slave controller changes the second direct current voltage in such a manner that voltages on the positive and negative terminals of the local device are opposite in phase and vary synchronously with the first direct current voltage; the feeding phase and the communication phase are repeated; the slave controller includes a power supply circuit, a voltage change detection circuit, a voltage control circuit, first and second constant current circuits, and a signal ground, the power supply circuit generates the second direct current voltage from the first direct current voltage, the voltage change detection circuit detects a change in the first direct current voltage and outputs a first signal corresponding to the change in the first direct current voltage to the voltage control circuit, the voltage control circuit changes the second direct current voltage in accordance with the first signal, the first constant current circuit is connected between the voltage control circuit and the positive terminal of the local device to feed a constant current to the positive terminal of the local device, and the second constant current circuit is connected between the negative terminal of the local device and the signal ground to draw the constant current from the negative terminal of the local device.