A communication system is provided with a power supply budget such that portions of a phone line side circuit may be powered from the TIP and RING phone lines while using standard electronic devices for the hookswitch circuits and the diode bridge circuit. For example, low voltage converters in the phone...http://www.google.com.tw/patents/US20030206626?utm_source=gb-gplus-share專利 US20030206626 - Low voltage circuits powered by the phone line
