| 摘要 |
An isolated, high impedance, DC current source is provided from a readily available AC type source. The DC current source includes an isolating transformer which receives the AC source signal and provides an isolated AC voltage signal therefrom, a resonant low pass filter which is tuned to the frequency of the AC type source and which takes the AC isolated voltage signal and generates therefrom an AC current source signal, and a rectifier which rectifies the AC current source signal to provide a DC current source signal. A voltage limiting clamp is preferably coupled to the rectifier in order to limit the output voltage to a desired level. The resonant low pass filter is preferably comprised of two substantially equally valued inductors coupled to respective poles of the secondary winding of the isolating transformer, and a capacitor which is coupled to both of the inductors. In one embodiment, the AC type source is a 5 V CMOS clock signal, and the output current source generates a sealing current of between 4 and 10 milliamps for telecommunications equipment. In another embodiment, the AC type source is chosen for a desired voltage and frequency, and a plurality of DC current source circuits are coupled to the AC type source in order to distribute power to repeaters or other remote equipment.
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