User's Manual

800MHz & VHF Cell Enhancers
Maintenance Handbook
H/book Number:-50-078001HBKM
Issue No:-
A
Date:-02/09/2004
Page:-
69 of 88
5.20 Dual DC/DC Converter (13-001803)
5.20.1 Description
This unit is employed where it is necessary to derive two fixed voltage power supply rails
from some higher voltage. Typically it is used to derive 5, 8, 12 or 15V from a 24V input.
The circuit is based upon a pair of LM257 series variable voltage regulators (LM2576, 12 &
15V & LM2575, 5V), which are each capable of supplying an absolute maximum of 1.5A
output current. Note that at full output current, the dissipation of the device must remain
within design limits, bearing in mind the voltage which is being dropped across it. The
maximum allowable dissipation will also depend on the efficiency of the heatsink on which
the device is mounted.
5.20.1 Technical Specification
PARAMETER SPECIFICATION
Operating Voltage: 21 – 27V DC
Output Voltage: 12V & 12V (typical)
Output Current: 1.0A (maximum per o/p)
Connections: Screw Terminal Block
operational: -10°C to +60°C Temperature
Range
storage -20°C to +70°C
PCB Size: 85 x 63mm