Ericsson 19A704647P1, Руководство по обслуживанию

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15. The P3 and P14 Power Supplies are for use on circuits
of nominal 240 volts AC. They are factory equipped
with an electric cordless plug connector. A terminat-
ing connector that meets local electrical codes should
be added.
16. Care should be taken when placing the unit in service
to insure proper top and bottom ventilation. A mini-
mum of 1/4 inch is required between the bottom of
the unit and the surface on which it sits.
INTRODUCTION
These power supplies were designed expressly to provide
power for the Delta Desktop/Wall station. They supply thir-
teen (13) amperes of direct current at 13.8 Volts. The output
is protected from both overcurrent and overvoltage. In addi-
tion, built in overtemperature protection prevents damage
from usage outside of the specified temperature range.
The circuit diagrams of these power supplies (part numbers
P11, P12 and P14) are the same, except for primary power
connections. The applications are:
Part 1, 11 - For rack Mounting (Delta type) - 120V 60Hz
Part 2, 12 - Table Mounting (Rubber Feet) - 120V 60Hz
Part 3 - Table Mounting (Rubber Feet) - 240V 50Hz
Part 4 - For rack Mounting (Delta type) - 240V 50 Hz
CIRCUIT DESCRIPTION
INPUT SECTION
Input power to the supply is provided from a 121 Volt,
50/60 Hertz (or 242 V, 50/60 Hz) line source connected
through the main power cord. The line is passed through fuse
F1, that limits the input current to 4 amperes. The input current
also passes through varistor RV1, a transient limiting device
that clamps the line at approximately 160 Vrms. This protects
the device from potentially harmful line voltage excursions.
FILTER AND BRIDGE SECTION
After passing through the input protection devices the line
voltage is applied to the primary winding to transformer T1.
The stepped down line voltage of approximately 35 Vrms, is
applied to the diode bridge D1 and filter capacitors C1, C2,
and C3. These devices convert the alternating current line to
approximately 25 Volts direct current.
FILTER AND OUTPUT REGULATOR
SECTION
The current then flows through the linear regulator section
of the supply. The linear regulator is composed of two func-
tional groups of components. The first group, the series pass
regulator group consists of Q1, Q2, R1, and R2. In order to
control the output voltage of the supply, the series pass tran-
sistors are operated as variable resistors. If the load on the
supply is increased, causing a drop in the output voltage, the
resistance of the series pass transistors is automatically de-
creased. This decrease balances the output voltage drop and
returns the output voltage back to the desired level.
In order to regulate the output voltage, two pass transistors
are used. R1 and R2 provide negative feedback to the emitters
of the respective transistors, balancing them and causing equal
current flow and equal power dissipation.
The second functional group is the series pass control,
consisting of U1 and Q3 in conjunction with their associated
bias resistors and decoupling capacitors. U1 continuously
monitors the output voltage developed through the interaction
of the load and the series pass transistors. When more output
voltage is required to maintain regulation, U1 increases drive
to transistor Q3. Q3 provides the amount of series pass tran-
sistor base drive necessary to decrease their resistance and
boost the output voltage back up to the desired value. This
continuous interaction between the control circuitry and series
pass stage forms a closed loop control group providing the
regulated output voltage to the power supply load. The closed
feedback loop is compensated by R4, C6, and C7 to provide
loop stability. Potentiometer R13 varies the amount of output
voltage fed back in the control loop thus allowing precise
adjustment of the output voltage at which regulation is main-
tained.
OVERCURRENT PROTECTION
Overcurrent protection is implemented via a current fold-
back scheme. Resistor R3 is used as a current sensing element.
The amount of voltage developed across this resistor is directly
proportional to the amount of current flowing to the load. This
sense voltage is applied to the regulator control integrated
circuit, U1, by means of R5, R6, and R7. As the current
through the sense resistor increases past 13.8 amps, the sense
voltage seen by U1 causes the value of both output voltage and
output current to decrease. This foldback approach to over-
current protection decreases the amount of power dissipated
across the series pass transistors during a faulted condition.
The maximum allowable short circuit current is less than five
(5) amps.
LBI-38751
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