Battery backup for AC powered DC supply

Abstract

A battery backup system for an AC energized DC supply has an AC line monitor for producing a pulse signal having a pulse width dependent on rise time of the AC signal and a frequency dependent on zero line crossings of the AC signal. The pulse signals are checked for frequency and pulse width by being used to control the charging time of a timing capacitor for a timer and to be compared with the pulse width of a predetermined reference pulse, respectively. The occurrence of a defect in the pulse signals stemming from either pulse testing criteria is effective to trigger an SCR circuit into conduction to connect a backup battery to the load devices to replace the DC power formerly being supplied by the AC line. After restoration of the AC power, the backup battery is removed following a fixed time delay to allow the AC powered DC supply to stabilize. A battery charging power supply is connected to the backup battery and is automatically switched between a battery "float-rate" and a "high-rate" charging operation following an AC outage and returned when the charging current indicates that the backup battery is fully charged.

Dependencies are inferred from the claim text.