Micropower Backup Supply Operates From Phone Line

摘要

Designers of electronic circuits for telephone systems are constantly enticed by the possibility of utilizing the "free" power provided by the telephone company. The catch involved in pulling off this feat is that this power is limited to 5 μA maximum when the phone is "on-hook" (that is, not in use). To complicate things further, the nominal 48-V dc line voltage can fluctuate over an approximate 24- to 58-V dc range.