Abstract: A power management circuit for use in a terminal interface device such as a modem which converts available power from a terminal or host device such as a computer into usable standby power for use when the terminal interface device is non-operational. The power management circuit is additionally comprised of a voltage regulator which, when a terminal interface device becomes operational, is enabled and regulates available voltage and current into usable power as available from the interfacing communication network. The preferred embodiment of the power management circuit is further comprised of a programmable hold current generator which enables a terminal interface device incorporating the power management circuit to be compatible with multiple communication networks having diverse hold current specifications. The use of power available from the communication network in generating the operational voltage greatly reduces interference injected onto the communication network.