| 摘要 |
A DC system (31) is fed by an external power source (6, 7). When power fails, circuits (32) in the system are to be rapidly alerted (S1) to save unstored information, before the input DC (S4) has fallen too low. A capacitor device (34) is connected to the system input (30) and a current (I1) in the capacitor connection (37) is detected (36). When power fails the current (I1) flows from the capacitor device (34) and a detection circuit (36) generates a corresponding signal. This signal is delayed a predetermined time interval into an alerting signal (S1), which is transmitted to the DC circuit (32). Delaying the signal before the alerting ensures that a very short fail in the DC voltage (S4), or ripple in this voltage, will not unnecessarily alert the DC circuit (32) to start saving information.
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