A DC/DC Converter for ISDN Terminals

In the field of power conversion for telecommunication equipment, ISDN involves various problems. One of them is to achieve the required efficiency of the DC/DC converter used to supply low power terminals such as digital telephones connected to the "S" bus. SAT has developped such a converter to equip digital telephone terminals designed for RENAN (the French experimental digital network). To fulfil the requirement of high efficiency in a wide range of output power and specially at very low output power, this converter works in two different modes : - free running frequency with fixed pulse-width for low power output corresponding to the stand by state of the terminal - fixed frequency PWM for higher output power corresponding to active states of the terminal. The control circuitry is achieved by simple low cost low power components.