Circuit for preventing simultaneous on operations

1. A circuit for preventing simultaneous ON operations at a relay drive apparatus, which includes a first relay having a first drive unit receiving drive current through a first resistor from a power supply and a first switch device connected with a first signal line to be driven by the first drive unit, a second relay having a second drive unit receiving drive current through a second resistor from said power supply and a second switch device connected with a second signal line to be driven by the second drive unit, and a controller having a first control signal output terminal for outputting a control signal to control the first drive unit and a second control signal output terminal for outputting a control signal to control the second drive unit, comprising:

a first diode;

a second diode;

a first transistor being connected through the first diode with the first drive unit for controlling ON/OFF operation by the control signal derived from the first control signal output terminal of the controller;

a second transistor being connected through the second diode with the second drive unit for controlling ON/OFF operation by the control signal derived from the second control signal output terminal of the controller;

a first junction point of the first resistor and the first drive unit;

a second junction point of the second resistor and the second drive unit;

a third junction point of the first diode and the first transistor;

a fourth junction point of the second diode and the second transistor;

a third diode, an anode of which is connected to the second junction point, a cathode of which is connected to the third junction point; and

a fourth diode, an anode of which is connected to the first junction point, a cathode of which is connected to the fourth junction point.

2. A circuit for preventing simultaneous ON operations at a relay drive apparatus, which includes a first relay having a first drive unit receiving drive current through a first resistor from a power supply and a first switch device connected with a first signal line to be driven by the first drive unit, a second relay having a second drive unit receiving drive current through a second resistor from said power supply and a second switch device connected with a second signal line to be driven by the second drive unit, and a controller having a first control signal output terminal for outputting a control signal to control the first drive unit and a second control signal output terminal for outputting a control signal to control the second drive unit, comprising:

a first diode being connected between the first resistor and the first drive unit;

a second diode being connected between the second resistor and the second drive unit;

a first transistor being connected with the first drive unit for controlling ON/OFF operation by the control signal derived from the first control signal output terminal of the controller;

a second transistor being connected with the second drive unit for controlling ON/OFF operation by the control signal derived from the second control signal output terminal of the controller;

a first junction point of the first resistor and the first drive unit;

a second junction point of the second resistor and the second drive unit;

a fifth junction point of the first drive unit and the first transistor;

a sixth junction point of the second drive unit and the second transistor;

a third diode, an anode of which is connected to the second junction point, a cathode of which is connected to the fifth junction point; and

a fourth diode, an anode of which is connected to the first junction point and a cathode of which is connected to the sixth junction point.

3. The circuit for preventing simultaneous ON operations according to claim 2 , wherein the first diode and the fourth diode have a same characteristic, and the second diode and the third diode have a same characteristic.

4. A circuit for preventing simultaneous ON operations at a relay drive apparatus, which includes a first relay having a first drive unit receiving drive current through a first resistor from a power supply and a first switch device connected with a first signal line to be driven by the first drive unit, a second relay having a second drive unit receiving drive current through a second resistor from said power supply and a second switch device connected with a second signal line to be driven by the second drive unit, and a controller having a first control signal output terminal for outputting a control signal to control the first drive unit and a second control signal output terminal for outputting a control signal to control the second drive unit, comprising:

a first diode;

a second diode;

a first transistor being connected with the first drive unit for controlling ON/OFF operation by the control signal derived from the first control signal output terminal of the controller;

a second transistor being connected with the second drive unit for controlling ON/OFF operation by the control signal derived from the second control signal output terminal of the controller;

a first junction point of the first resistor and the first drive unit;

a second junction point of the second resistor and the second drive unit;

a third transistor being connected through the first diode with the first junction point and through the second diode with the second junction point;

a third diode being connected between the first control signal output terminal and the third transistor; and

a fourth diode being connected between the second control signal output terminal and the third transistor.