| 摘要 |
The mains device is provided for an electric door opening system. The system uses a constant voltage of a predetermined, relatively small amplitude and also an alternating voltage of a predetermined, relatively small amplitude to supply different modules, such as bell buttons, a door opener, an audio signal generator and intercom units. The device has transformer connected at its primary side to the mains ac voltage. An output ac voltage line is connected to the secondary side of the transformer, with a phase line (1) and an ac voltage null line (2). A bridge rectifier (4) is connected at the secondary side of the transformer. A constant voltage regulating circuit (8) is connected to the output terminals (5,6) of the rectifier (4) and to a constant voltage neutral line (7). The regulating circuit (8) has an output line (9) for the controlled voltage. Only one neutral lead connection (10) is provided for both the ac and dc neutral lines (2,7). The transformer only has one secondary terminal (11) to which the phase line (1) and the ac neutral line (2) and the rectifier inputs (3) are connected. A neutral line switch over contact (12) is provided between the dc neutral line (7) and the ac neutral line (2). A single output terminal (13) is provided to output ac voltage and dc voltage. A phase line switch over contact (14) is provided between the output terminal (13) and the phase line (1) and dc output line (9). The two switch over contacts (12,14) normally close the dc circuit. When an ac load is connected to the neutral line connection (10) and the output terminal (13) causing current flow in the regulating circuit (8), the switch over contacts (12,14) change and close the ac circuit. When the ac load is removed the contacts (12,14) switch back to the dc circuit. |
