Samlex America SEC-4825BRM - Manual (Page 7)

6 | SAMLEX AMERICA INC. SAMLEX AMERICA INC. | 7
Section 3 | Design & Principle of operation
Fig. 2.2 Dimensions
DESCRIPTION
SEC-4825BRM is a Switch Mode Power Supply (SMPS), which converts 120 VAC, 50/60 Hz
to 48VDC Nominal (actually 54.8VDC at no load to 54.2V at 25A). It has additional provi-
sion for 48V battery backup with 2A charging in conjunction with external 48V Lead
Acid Battery (not supplied).
FEATURES
• 19”, 2U (3.5”) height Rack Mount design
• Advanced Switch Mode Technology
• N+1 Redundancy: 5 x 5A Power Supply Modules operate in parallel under
forced current share control
• Remote monitoring through Opto Isolated, Open Collector / Open Emitter
output signals
• Reliable, 48 VDC Uninterruptible Power Source (DC UPS) in conjunction
with external 48V Lead Acid backup Battery (not supplied)
• High efficiency and compact
• Protected against short circuit, overload, over voltage and over temperature
PRINCIPLE OF OPERATION
The unit consists of 2 Sections - Switch Mode Power Supply (SMPS) Section and Battery
Backup and Charging Section.
The SMPS Section is designed using advanced switch-mode technology and active load
share circuitry for high reliability, high efficiency and minimum size and weight. It is
modular in construction consisting of 5 x 5A Power Supply Modules (PSM) that are
connected in parallel and operate under forced current share control to deliver a total
of 25A. Each PSM is a stand-alone, 55V Power Supply, which delivers up to a maximum
of 5A continuous. By equalizing the output currents, uniform thermal stress of the
individual PSMs is ensured which has utmost importance for long-term reliability of elec-
tronic components. The operating principle of current share mechanism is to measure
the output current of each PSM and to modify the output voltages of the 5 PSMs until
all the 5 PSMs deliver equal output current. Typically, the output currents of the 5 paral-
leled PSMs will be within 10% of each other at full output current. The module with
the highest voltage at switching ON automatically assumes the role of a Master and the
others operate as Slaves. Each PSM is required to be interconnected with one another to
a common “SHARE BUS” through a pair of parallel pins marked “JUMP 1” and jumper
wires (Fig. 3.5).
For proper operation of Current Share Control Circuitry / Master - Slave operation, a mini-
mum load current is required to flow through each PSM to produce adequate feed back
signal. This minimum pre-load current is provided by the sum of the currents drawn by
the 2 cooling fans and by an internal static load resistor connected across the load output
terminals. This internal pre-load current* is kept to the minimum to reduce dissipation.
11001-SEC-4825BRM-0114.indd 7 14-01-07 1:15 PM