User's Manual

EX7100 Technical Manual - Module Descriptions
©1999 Exicom Technologies (1996) Ltd 7-69 Issue 3 - May 2001
7.14 Isolated Power Supply Type 2990
7.14.1 General
Isolated power supply module Type 2990 provides DC power to the six-channel
Exchange Interface circuit board Type 2967 and six-channel Subscriber Interface circuit
board Type 2971 as required.
The output rails of the power supply are isolated from the input rail; the isolated supply
can withstand 3.5kV potential difference between input and output.
7.14.2 Description
The module consists of two current-mode flyback converters, switching at approximately
120kHz.
One converter provides the various +5V and –5V rails (analogue and digital supplies) The
other converter provides the -48V rail to power the telephone line and +100V for the ring
voltage generator on the Subscriber Interface circuit.
Both supplies are regulated via optocouplers. None of the output rails are individually
current-limited, but each converter incorporates current limiting in the control IC. This
limits the maximum power that can be delivered to the outputs. All rails except the +100V
rail incorporate LC noise filtering.
A 10-way output connector provides access to the various output rails.
The module runs off the +24V rail provided by the main Power Supply Type 2964 (refer to
Section 7.2). The input connector carries both +24V and +5V.
Note: The +5V input is not used on the module board, but is passed directly onto a
secondary power connector for the non-isolated side of the Interface board.
7.14.3 Testing and Fault Diagnosis
The output rails of the isolated power supply can not be monitored via the front panel. If a
fault is suspected in the isolated power supply, it requires manual testing.
The Isolated Power Supply Module Type 2990 contains a +100V
power rail that is potentially dangerous or lethal. To ensure personal
safety, please observe caution when operating the EX7100 terminal
with the covers removed.