| 摘要 |
<p>PROBLEM TO BE SOLVED: To control an operating state of each relay to a desired state even when a specific output port, in which a control signal for controlling the relay appears, becomes a high-impedance state.SOLUTION: In a relay control device controlling on and off of a plurality of relays 1, 2, 11, and 12 connecting between a high-voltage-system circuit and a low-voltage-system circuit, pull-down circuits 31 to 34 are connected so that input potentials of buffer circuits 6a, 6b, 16a, and 16b approach a constant potential when output ports P1 to P4 of a CPU 20 become high impedance. Even when a microcomputer does not operate, on and off states of each relay can be surely controlled, thereby preventing flow of a high-voltage current from a high-voltage system to a low-voltage system after the plurality of relays simultaneously turn on. The combination of a pull-down circuit 41 and a pull-up circuit 42 surely performs discharging of charges of a flying capacitor 9 at the time of stop of the CPU 20.</p> |
