Nautel NAB05E, Технические инструкции

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48 VOLT BATTERY CHARGER
NAB05E
Page 2-3
01 September 2004
'control voltage', the comparator's output will switch
to a low (dc reference) level and cause the switching
transistor to turn on. A positive voltage, 'thyristor
control' pulse will be applied to the control gate of
both thyristors in the switched full-wave rectifier
circuit. Since the ramp voltage increases linearly with
time and it is reset to the dc reference voltage, at the
start of each half cycle of the ac voltage applied to the
unregulated 23 volt dc bridge rectifier, the level of the
'control voltage' will determine at what point of time,
relative to the start of each ac voltage half cycle, the
leading edge of the 'thyristor control' pulse will occur.
As the 'control voltage' goes more positive, the
leading edge of the 'thyristor control' pulse will occur
at a progressively later period of time. As the 'control
voltage' goes less positive, the leading edge of the
'thyristor control' pulse will occur at an earlier period
of time.
2.2.10 FULL-WAVE RECTIFIER
OVERVIEW: The switched full-wave rectifier
circuit produces a dc voltage that maintains the battery
charging current at the preset, desired level when a
'thyristor control' pulse is applied. The circuit consists
of two thyristors that have the ac voltage on the centre
tapped secondary (75-0-75 volts RMS ac) of the ac
power supply applied to their anodes. The voltage on
each anode is 180 degrees out of phase with the other;
but, since they are obtained from the same transformer
as the ac power source for the unregulated 23 volt dc
bridge rectifier, the crossover point for each half cycle
will be synchronized with the start of the ramp
waveform output of the ramp generator. The
'thyristor control' pulse will occur at some point of
time during each half cycle. Each thyristor will only
turn on when its anode is positive relative to its
cathode and it will remain on for the remainder of that
half cycle. The output of the switched full- wave
rectifier circuit will be dc voltage pulses with an
average value determined by the period of each half
cycle that the thyristors are turned on. When the
'thyristor control' pulses occur at the appropriate time,
this average dc voltage will maintain the battery
charging current at the desired, preset level. A choke
is installed in the centre tapped ac return path to filter
the average dc voltage. It also contains a free
wheeling diode that prevents oscillations when the
'thyristor control' pulses are removed and the current
in the choke collapses.
DETAILED DESCRIPTION
2.3
The following provides an in-depth under-
standing of complex or non-obvious circuit functions.
The descriptions are keyed to the block diagram
referenced in paragraph 2.2 and expand on the
associated block diagram descriptions.
2.3.1 AC POWER SUPPLY: The ac power
source (115 volts ac RMS, 60 Hz or 230 volts ac
RMS, 50 Hz) is connected between TB1-4 (line) and
TB1-5 (neutral) with the ac ground connected to the
safety ground stud. The ac line is applied thru EMI
filter U2 thru
POWER
switch S1, thru fuse F1, thru
TB1-1 to one side of power transformer T1's primary
windings. The ac neutral is connected to the other
side of T1's primary windings thru TB1-2. Power
transformer T1 has two identical 115 volt primary
windings. Two sets of secondary windings provide
the step down voltages required by the battery
charger's dc power supplies. One set of secondary
windings provides 17.5 V ac, RMS and the other set
provides a centre tapped 150 (75-0-75) V ac RMS.
2.3.2 V DC POWER SUPPLY: 17.5 V ac,
RMS, from power transformer T1, is applied to
full-wave bridge rectifier A1U1. The resultant output
of A1U1 is a nominal 23 V dc, which is not regulated
and contains a ripple component that is twice the
frequency of the ac power source. This ripple dc
voltage is applied to the inverting input of comparator
A1U3A and thru diode A1CR1 to smoothing
capacitor C1. Smoothing capacitor C1 smooths the
unregulated 23 V dc output to an acceptable level,
while RF bypass capacitor A1C1 removes any high
frequency component. The negative side of the 23 V
V dc power supply is not connected to chassis ground
but is connected to the positive voltage side of the
battery charging voltage (positive battery terminal).
This point is the dc reference level for all of the logic
circuits. Light emitting diode DS1 will turn on when
the 23 V dc power supply is producing an unregulated
23 V dc output.
2.3.3 15 V DC POWER SUPPLY: The
smoothed unregulated 23 V dc is applied to the input
of 15 V dc regulator A1U1. The output of 15 V dc
regulator A1U1 is maintained at +15 V dc with
respect to the dc reference level, regardless of the
fluctuations in the unregulated 23 V dc, provided it
remains above 15 V dc.