Sony HDCAM HDW-F900R Maintenance Manual page 86

1-26-8. Power Supply Systems (CNB-23 Board,
RE-186 Board, and RE-187B Board)
CNB-23 board
This controls distribution of the input +12 V power to the
respective circuit boards.
. Power ON/OFF Control
The L PWR SW ON signal enters IC107 of the CNB-23
board via the IFA-19G board and the MB-1096 board that
turns on Q107. As Q107 is turned on, the battery +12 V or
the EXT DC IN +12 V is supplied to the respective
circuits.
IC107 of this unit receives at the same time the H POWER
HOLD signal from the FP-152 board after the main power
of this unit is turned on. Therefore, Q107 is kept on even if
the L PWR SW ON (L) signal is set to OFF (H).
In order to turn off the main power of this unit, the H
POWER HOLD signal must be opened and goes to "L".
When the FP CPU (IC816) of the FP-152 board detects the
POWER SW OFF, it waits for completion of the VTR
operations if any VTR operations are in progress, and sets
the POWER HOLD signal to "L" to turn off the main
power of this unit.
. Protection from Excess Input Voltage
The VOLTAGE DETECT (IC101) monitors UN SW +12
V through D105. If the UN SW +12 V exceeds approxi-
mately +18 V, it outputs the PROTECT signal (L) from its
pin-4 to turn off the +12 V power. (Except UN SW +12 V
for the FP-152 board.)
This circuit does not have a latch function so that the
power will be recovered immediately after the input power
voltage returns to +18 V or less.
. Battery/EXT DC selection
The connector insert detection switch that is fitted with the
EXT DC IN connector (XLR 4-pins) is used to select
either battery or EXT DC input.
The output signal from this switch passes through IC103 to
IC105 and is sent to the FET CONTROLLER (IC109) that
finally selects ON/OFF of the FETs (Q110 to Q112 and
Q114 to Q116 : ON when battery is in use, Q120 to Q125 :
ON when EXT DC power is in use).
In this IC109, a step-up circuit (Vcc +8.5 V) that drives
the N-CH MOS FET gate is employed.
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. Excess current detection
The output circuit of the UNREG +12 V from the CNB-23
board has excess current detection resistors R142, R143
and R147. A voltage drop at the resistors is detected by the
FET CONTROLLER (IC109). When the voltage drop at
the resistors exceeds 200 mV, the power supply circuit
enters the SHUT DOWN state.
Another SHUT DOWN signal is the H SHUT DOWN
signal that is supplied from the RE-187B board. If any one
of the DC-DC converter outputs is shorted, the power
supply circuit enters the SHUT DOWN state except UN
SW +12 V.
Since the FET CONTROLLER (IC109) on the CNB-23
board has a latch function, the power supply does not
restore automatically. The main power of the unit needs to
be turned off once and back on.
. Protection against input power connection of reverse
polarity
If the input power is connected in reverse polarity, FET
(Q101) is turned off so that the GND lines of the control
system circuits are disconnected. Thus the control circuits
are protected and supply of +12 V power to the respective
circuits is stopped.
DC-DC converter
The DC-DC converter consists of two circuit boards, the
RE-186 board and RE-187B board. Neither of these two
boards can be operated independently.
. PWM clock signal
The PWM POWER CONTROL (IC202) on the RE-186
board generates the master clock signal (100 ± 10 kHz) for
all of the controller ICs (IC101, IC202, and IC301 on the
RE-186 board and IC102 and IC103 on the RE-187B
board) and distributes it.
. Input voltage monitoring circuit
The RE-187B board has the input power voltage monitor-
ing circuit (IC105). When the input power voltage stays
within the specified range, the powers are supplied to the
respective controller ICs (IC101, IC202, and IC301 on the
RE-186 board and, IC102 and IC103 on the RE-187B
board).
The power supply circuit starts up when the input power
voltage is within the range of +10.4 V to +18.8 V. Once
the power supply circuit has started up, it keeps operating
until the input power voltage decreases below the lower
limit (+9.5 V).
HDW-F900R/V1 (E)