| 摘要 |
A power supply includes a dc voltage source (110) and a circuitry which powers a modem data access arrangement (DAA) (102) while preventing dc voltages from being applied to a private line (104). The circuitry permits ac signals from the modem to travel substantially unhindered over the private line (104). A first embodiment includes a split winding transformer (112), and a capacitor (122) coupled across the voltage source (110). A first primary winding (116) of the transformer (112) is coupled in series between a positive pole (124) of the voltage source (110) and a positive input to the DAA (102) and a second primary winding (118) of the transformer (112) is coupled in series between a negative pole (128) of the voltage source (110) and a negative input to the DAA (102). A second embodiment includes a standard transformer, an inductor and a capacitor. A third embodiment includes two capacitors and two inductors.
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