Power sources for ISDN NT boards

SGS-THOMSON Microelectronics is now offering a pair of fully assembled and tested power supply units specifically designed for use in ISDN network termination boards. Meeting all appropriate European Telecommunications standards such as ETS 300 012, ETS 300 047 and EN60950, the GS1T70-D540/2 DC-DC converter and the GS5AC-40 AC-DC converter provide a fully integrated, cost-effective solution to the power supply needs of ISDN NTBA (Network Termination Basic Access) equipment.

The ISDN NT board needs two power rails: a 40V supply for the "S" interface and a 5V supply for logic devices. The 5V supply is obtained from the telephone line (fed by the central office's battery) through the DC-DC converter and the 40V supply is normally obtained from the mains input using the AC-DC type.

However, in case of mains failure, the NT board has to derive an emergency 40V supply from the line battery. In SGS-THOMSON's solution, the AC/DC converter generates two separate 40V outputs: a 110mA output - the normal power supply of the "S" interface - and an auxiliary 10mA output to drive an LED and the relay which switches to the emergency power supply in case of a mains failure. The DC/DC converter is fed by the telephone line. It also generates two independent outputs: a 5V/72mA output and a 40V/12mA output (the emergency power supply).

Both converters feature wide input voltage ranges, output short circuit protection and input and output filtering. The GS5AC-40 operates with mains inputs from 180 to 264VRMS and is protected against continuous output short circuits. It is provided with an input filter to meet EMI requirements and an ETSI-compliant output filter. Housed in a compact package measuring 80x43x30mm, it can withstand a voltage of 3000VRMS for 60 seconds between input and output.

The GS1T70-D540/2 DC/DC converter, which measures 50.8x50.8x18mm, has a DC input range of 28-115V, allowing it to operate over the whole range of line termination battery voltages and line resistances. The highly efficient design maintains a minimum efficiency of 80% at full load and the device is fully protected against short circuits; a short circuit on the 40V output will not affect the 5V output and the input power never exceeds the limits of the ISDN specification. The 40V output is fully insulated from both the input and the 5V output, with an insulation voltage of 3000VRMS for 60 seconds.

SGS-THOMSON is a major supplier of integrated circuits and discrete power devices for use in power supplies and its engineers have considerable experience in the design of PSU systems. The GS1T70-D540/2 and GS5AC-40 allow designers of ISDN NT boards and other telecoms equipment to capitalize on this experience.

Top