Power line communication device, in-vehicle device and in-vehicle system

1. A power line communication device, comprising:

a power source;

a power line; and

a master station that modulates a supply voltage supplied to the power line according to transmission data to be transmitted,

wherein the master station includes

a modulation capacitor that is precharged with a modulation amplitude voltage,

a switch unit that determines a polarity of the modulation capacitor connected to the power line according to the transmission data, and

an inductor that is connected between the power source and the power line.

2. The power line communication device according to claim 1 ,

wherein the modulation capacitor is connected between the power source and the power line, and a polarity of the modulation capacitor connected to the power line is inverted by the switch unit.

3. The power line communication device according to claim 2 ,

wherein the inductor is connected in parallel with the modulation capacitor.

4. The power line communication device according to claim 3 ,

wherein the master station includes

a capacitor voltage monitoring unit that monitors a voltage between terminals of the modulation capacitor,

a capacitor charging unit that connects a current load to a negative terminal of the modulation capacitor when the voltage between the terminals is lower than a predetermined voltage, and increases the voltage between the terminals.

5. The power line communication device according to claim 4 ,

wherein the master station includes a capacitor discharging unit that connects a current load to a positive terminal of the modulation capacitor when the voltage between the terminals is higher than a predetermined voltage, and reduces the voltage between the terminals.

6. The power line communication device according to claim 5 ,

wherein the master station includes a transmission line encoder that changes an encoding format of the transmission data when the voltage between the terminals deviates from a predetermined voltage.

7. The power line communication device according to claim 3 ,

wherein a voltage of the power source and a voltage of the power line that is not modulated are the same.

8. An in-vehicle device for modulating a supply voltage supplied to a power line according to transmission data to be transmitted, the in-vehicle device comprising:

a modulation capacitor that is precharged with a modulation amplitude voltage;

a switch unit that determines a polarity of the modulation capacitor connected to the power line according to the transmission data; and

an inductor that is connected to the power line and supplies a predetermined voltage to the power line.

9. The in-vehicle device according to claim 8 ,

wherein the modulation capacitor is connected between a power source and the power line, and a polarity of the modulation capacitor connected to the power line is determined by the switch unit.

10. The in-vehicle device according to claim 9 , further comprising:

a capacitor voltage monitoring unit that monitors a voltage between terminals of the modulation capacitor;

a capacitor charging unit that connects a negative electrode of the modulation capacitor to a current load, and charges the modulation capacitor when it is detected that the voltage between the terminals of the modulation capacitor is smaller than a predetermined voltage as a result of monitoring by the capacitor voltage monitoring unit; and

a capacitor discharging unit that connects a positive electrode of the modulation capacitor to a current load and discharges the modulation capacitor when it is detected that the voltage between the terminals of the modulation capacitor is greater than a predetermined voltage as a result of monitoring by the capacitor voltage monitoring unit.

11. The in-vehicle device according to claim 10 ,

wherein the inductor is connected between the power source and the power line,

wherein the switch unit includes a switch for electrically connecting the power source and the power line when the supply voltage is not modulated, and

wherein, when the supply voltage is not modulated, the switch and the inductor are connected in parallel between the power source and the power line.

12. An in-vehicle system, comprising:

a master station that modulates a supply voltage supplied from a power source according to transmission data to be transmitted; and

a plurality of slave stations that are connected to the master station by a power line,

wherein the master station includes

a modulation capacitor that is precharged with a modulation amplitude voltage,

a switch unit that determines a polarity of the modulation capacitor connected between the power source and the power line according to the transmission data, and

an inductor that is connected between the power source and the power line.

13. The in-vehicle system according to claim 12 ,

wherein the master station further includes

a capacitor voltage monitoring unit that monitors a voltage between terminals of the modulation capacitor,

a capacitor charging unit that connects a negative electrode of the modulation capacitor to a current load, and charges the modulation capacitor when it is detected that the voltage between the terminals of the modulation capacitor is smaller than a predetermined voltage as a result of monitoring by the capacitor voltage monitoring unit, and

a capacitor discharging unit that connects a positive electrode of the modulation capacitor to a current load and discharges the modulation capacitor when it is detected that the voltage between the terminals of the modulation capacitor is greater than a predetermined voltage as a result of monitoring by the capacitor voltage monitoring unit.

14. The in-vehicle system according to claim 13 ,

wherein the switch unit includes a switch for electrically connecting the power source and the power line when a supply voltage is not modulated, and

wherein, when the supply voltage is not modulated, the switch and the inductor are connected in parallel between the power source and the power line.

15. The in-vehicle system according to claim 14 ,

wherein the plurality of slave stations include a coil driven based on the supply voltage of the power line, and a communication circuit that controls driving of the coil based on the transmission data.