Ericsson 19A149978P1, Maintenance Manual, Page: 6 / 18

DESCRIPTION
The ERICSSON GE MASTR

II Base Station Power
Supply provides up to 435 watts to power the base station
receiver, systems circuitry, and transmitter. The power sup-
ply normally will be used to provide power to a MASTR II
Base Station with a maximum of 29 Amps to the power am-
plifier and 4 Amps for the Receiver/systems circuitry. The
supply can also optionally be used to power a 225 watt
power amplifier. In this case the supply is connected only to
the power amplifier and will provide a maximum of 33
Amps.
The 60 Hz Model (19A149978P1) operates from a
nominal 121 Vac, 60 Hz source. If a 208/220/240 Vac 60 Hz
Source is to be used, an external step-down transformer
(similar to 19C307148P1) must be used with the 978P 1
supply. The 50 Hz Model (19A149978P2) provides the
same outputs as the ’978P1 supply but operates from a
nominal 230 Vac, 50 Hz source. The output voltage will
change a maximum of + 1.6% for each + 1.0% change in
the input line frequency.
The power supply’s step-down ferroresonant trans-
former provides excellent line voltage regulation. For the
rated input line voltage range (
±
20% for P1
±
15% for P2),
the output voltage will not vary more than 2 %. A ferroreso-
nant power supply provides inherently excellent line voltage
surge protection, and reduced parts count for high reliability.
No active semiconductor devices are used which could re-
duce reliability.
The output voltage will vary depending on the load cur-
rent that the supply is being asked to source. As the load
current rises, the output voltage will drop. Typically the out-
put voltage will be 13.2 volts for a 33 Amp load, less than
16.0 volts for a 3 Amp load, and less than 16.7 volts for no
load.
The operation and servicing of the power supply are
completely accessible from the front. The ON/OFF switch
and all fuses are located on the front panel. The low profile
slot type fuse holders contain the primary fuse F1 (F1 & F4
for 978P2) and the low current output fuse F3. The high
current output fuse F2 is mounted behind the front panel
fuse cover. The primary fuse F1 (F1 & F4 for 978P2) pro-
tects the input wiring to the ferroresonant transformer (10
Amps for P1, 5 Amps each for P2). The output fuses F2 (40
Amps) and F3 (5 Amps) provide external overload protec-
tion.
The 60 Hz supply provides a courtesy dual AC recepta-
cle. The primary line current fuse (F1) also provides over-
current protection for the dual receptacle. The 60 Hz supply
draws 5 Amps under nominal conditions and 7 Amps under
all extremes. Thus, the dual courtesy receptacles are rated to
provide a line current of 3 Amps.
CIRCUIT ANALYSIS
In the 60 Hz power supply (978P 1), the ON/OFF switch
(S1) provides line voltage to the power supply through the
primary line fuse F1. In the Rev. B version, line voltage
flows through F1 to the courtesy receptacles prior to S1.
This allows line voltage to always be available at the recep-
tacles. In previous models (Rev. A and earlier), S1 applies
line voltage to F1 and the courtesy receptacles in turn. Cur-
rent then flows through the primary of step-down trans-
former (T1) via the 200
°
C thermal fuse. The thermal fuse
would only open in the unlikely event that an internal short
would develop in the transformer. The Varistor (VR1 - 150
V rating) provides additional input line voltage suppression.
In the 50 Hz power supply (978P2), the ON/OFF switch
(S1) is a DPST type switching both primary AC lines. In ad-
dition, both input lines have 5 Amp fuses (F1 and F4). The
Varistor (VR1 - 275 V rating) provides additional input line
voltage suppression. When power is applied, current flows
through the primary of step-down transformer (T1) via the
200
°
C thermal fuse. As in the 60 Hz model, the thermal fuse
will open if the transformer develops an internal short.
The step-down transformer is a ferroresonant type which
has inherently good input line voltage regulation - eliminat-
ing the need for additional high-current regulators. C1
serves as a resonating capacitor across the secondary taps of
the transformer.
The transformer steps the input voltage down to ap-
proximately 14 volts (for a 33 Amp load) and 16 volts (for a
3 Amp load). It then applies the stepped-down voltage to the
full wave rectifier circuitry consisting of D1A,B through
D3A,B and the high current filter. The rectifiers are dual di-
ode packages and are mounted on heat sink HS1.
The high current filter consists of C2-C7 and L1. It is
designed to reduce the output ripple to less than 100 mV p-p
for any current load up to 33 Amps. It also keeps transient
responses greater than 11 and less than 18 volts. Resistor R1
is a 10 ohm, 50 watt resistor that serves two functions. One,
it acts as a bleeder resistor to discharge the capacitors when
the supply is turned off. Two, it provides a minimum current
A ferroresonant power supply is designed to work spe-
cifically at a given frequency. The 60 and 50 Hz sup-
plies should be used at their nominal frequency
±
2 Hz.
NOTE
LBI-38550
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