| 摘要 |
PROBLEM TO BE SOLVED: To provide a power switching circuit equipped with a contact protective circuit where a countermeasure is applied so that the contact of a power switching relay may not fuse by rush currents during changeover of a power source. SOLUTION: In the case that a normal power source B1 goes off and that the power voltage supplied to load 3 is switched from the normal power source B1 to an auxiliary power source B2, the operation contacts R1 and R2 within a power switching relay 2 are opened, and then the exciting circuit 11b within a contact protective circuit 11 moves slowly to switch the power voltage supplied from the normal power source B1 over to the power voltage supplied from the auxiliary power source B2 and supply it to the load 3. Accordingly, the rush current generated at switching from the normal power source B1 to the auxiliary power source B2 flows in condition that the recovery contacts R3 and R4 within the power switching relay 2 are closed, after passing the solid state relays SSR3 and SSR4 within the contact protective circuit 11, so the occurrence of trouble such as the abrasion, fusion, etc., of the recovery contacts R3 and R4 within the power switching relay 2 can be prevented. |
