Broadcast Electronics AM-2.5E, User Manual

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1-1
SECTION I
POWER SUPPLY THEORY OF OPERATION
1-1.
INTRODUCTION.
1-2. This section presents a general description of the Broadcast Electronics AM-2.5E/AM-5E
transmitter power supply assembly.
1-3.
GENERAL DESCRIPTION.
1-4. DC operating potentials for the RF power modules are provided by power supply assem
blies (refer to Figure 1-1). The power supply assembly consists of: 1) a power supply cir
cuit board and 2) filter and transformer components located on a power supply panel.
One power supply assembly provides dc operating potentials for one power block. The
AM-2.5E transmitter is equipped with 1 power supply assembly. The AM-5E transmitter
is equipped with 2 power supply assemblies.
1-5. The modular design of the power supply assembly allows the power supply circuit board
to be removed from the transmitter for maintenance. The following text presents a de
scription of the power supply circuit board and the components located on the power sup-
ply panel assembly.
1-6.
AC INPUT.
1-7. AC power from the ac input switch is applied through fuses F6 and F7 to power trans-
former T1. Fuses F6 and F7 protect the circuitry from over-current conditions. Trans
former T1 consists of: 1) a single primary winding and 2) five secondary windings. The
transformer is designed to provide low-voltage ac samples for application to five conven
tional bridge rectifier circuits.
1-8.
CONVENTIONAL RECTIFIER CIRCUITRY.
1-9. AC power from a winding of power transformer T1 is applied to bridge rectifier D11. D11
rectifies the ac potential into an unregulated 30V dc supply for application to the RF pow-
er module power amplifier circuit boards. Capacitor C21 provides filtering for the supply.
AC power from a second winding of transformer T1 is applied to bridge rectifier D10. D10
rectifies the ac potential into an unreg20V dc supply for the power supply circuit
board circuitry. Capacitor C20 provides filtering for the supply. AC power from a third
winding of ac power transformer T1 is applied to bridge rectifier D9. D9 rectifies the ac
potential into an unreg20 volt dc supply for application to: 1) the modulator cir-
cuit board and 2) to regulator U3. U3 is a +15 volt dc regulator. The output of U3 routed
for application to the components on the power supply circuit board. AC power from a
fourth winding of power transformer T1 is applied to bridge rectifier D12. D12 rectifies
the ac potential into an unreg15V dc supply for application to: 1) the power sup-
ply circuit board and 2) regulator U4. U4 is a +12 volt dc regulator. The output of U4
routed for application to the components on the power supply circuit board. An ac sample
from the winding is routed for application to a soft-start circuit. Capacitor C15 provides
filtering for the supply.
1-10.
SOFT-START CIRCUIT.
1-11. An ac sample from the winding of T1 is also routed to a soft-start circuit. The soft-start
circuit is designed to eliminate component stress during turn-on by limiting the current
in-rush. The circuit consists of an ac line detection/synchronization and soft-start control
circuits.