Schalt-Stromversorgungssystem für zwei oder mehrere eingangsseitige Spannungspegel

摘要

The switching power supply has a transformer 2 with a first primary winding connected via a rectifier 1 to a main AC source, and a second primary winding coupled to a backup battery which provides a lower voltage than the rectifier 1. A monitor circuit 7 changes the switching circuit from operation from the rectifier 1 to operation from the battery on detecting an interruption caused by the AC source falling below a predetermined level, or the output of the switching supply falling below a predetermined level, or the main source approaching an overload condition. The output may be regulated by a first PWM circuit 3 controlling a first switching transistor 4 connected to the first primary winding, there being a second switching transistor 6 connected to the second primary winding and controlled by a second PWM circuit 5 which is enabled by the monitor 7 when it senses an interruption. In an alternative embodiment, (Fig. 5) there is only one PWM circuit (3) which controls a switching transistor (4) commonly connected to both primary windings, and the battery is connected to the second primary winding via a switch (8) when the monitor circuit (7) senses an interruption.