Sony HDCAM HDW-F900R Maintenance Manual page 82

. Power supply voltage measuring circuit
The power supply voltage measuring circuit (IC805) uses
the DA output data from the FP CPU (IC816). The two
types of DC signal are output from the DA of the FP CPU
(IC816), and are used to change the voltage at IC805 (pin-
1) of the FP-152 board so that the voltage measurement
ranges are switched between the range of +9 V to +14 V,
and the range of +12 V to +17 V. The result of the voltage
measurement is sent to the SS CPU (IC1) in the form of a
voltage value where the remaining amount of battery and
remaining data for display are calculated by the SS CPU
(IC1) on the SS-92G board. The created data is sent back
to the FP CPU (IC816). The FP CPU (IC816) shows the
remaining data at every serial communication event.
. PWM power supply circuit for FAN/FP circuit
The PWM control loop (Q808: Open Loop) precisely
controls the supply voltages by using the switching power
supply circuit. Because the voltage input at the primary
circuit of the power supply circuit is supplied from battery,
the input voltage changes significantly. Because of the
significant change of input power voltage, the cycle of the
PWM signal is changed in accordance with the result of
battery voltage measurement so that the FAN power
supply voltage is kept constant. The camera CPU (IC27) of
the AT-172 board that measures the CCD temperature also
determines the FAN control voltage. It sends the com-
mands through the SS CPU (IC1).
The switching circuit of the PWM circuit is shared so that
it can act as a power supply circuit for the FP microproces-
sor (so that the FP CPU (IC816) can work during power-
off) and the power supply circuit for the peripheral circuits.
The consumption current is reduced so that the +6 V
power is first generated by the PWM circuit. After that, the
series regulator circuit is activated. When the main power
is turned on, the +5 V power from MB-1096 is sent to the
input circuit of IC806 to IC808 of the FP-152 board. When
the main power is turned off, +6 V power is input. The
output signal from IC808 and the diode D810 are connect-
ed as an OR gate so that the power supply of +5 V-2 is
supplied all the time.
The output signal from CN107 (pin-38) of the FP-152
board is used to drive the fan. The FP CPU (IC816) can
operate during power-off from the power supplied from
CN107 (pin-39, pin-40) of the FP-152 board.
. Soft control circuit at power-off
The FP CPU (IC816) detects the switch information. Only
when the FP CPU (IC816) and the SS CPU (IC1) of the
SS-92G board become ready to turn off, the main power
can be turned off. The FP CPU (IC816: pin-90) accepts the
input signal from the POWER switch. The FP CPU
(IC816: pin-91) supplies the output signal for power-off.
Only when this signal and the H_POWER_HOLD (IC816:
pin-91) signal goes "L", the main power can be turned off.
However, the main power can be turned on simply by
turning the POWER switch ON.
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. FP CPU backup circuit
The FP CPU (IC816) is connected to a coin battery so that
the data in the internal RAM is kept saved even after the
power is turned off. By saving the system data, the FP
CPU (IC816) can start up very quickly when the power is
turned on.
IC813, IC810 and IC812 on the FP-152 board are identical
+2.5 V threshold voltage detector ICs. Because IC813 has
resistors R845 and R846, the detection voltage is +3.05 V.
Since IC810 has the delay circuit consisting of R838 and
C829, detection by IC810 is delayed after IC812.
The delay of detection is used as follows. A drop in the
voltage that is supplied to the CPU is detected by IC813
first and the processing to enter the STANDBY mode
finishes. Next, IC812 creates the hardware STANDBY
state (clock signal stops). Lastly, the FP CPU (IC816)
enters the reset state by IC810 waiting for the next power-
on. When the power is turned on, the STANDBY is
released, the clock signal oscillation starts and then reset is
released.
. Backup lithium battery voltage measurement circuit
The FP CPU (IC816) measures the output voltage of the
backup lithium battery BT101 (BP-33 board). When the
battery-end is detected, the low-voltage information is sent
to the SS CPU (IC1) of the SS-92G board. Because this
battery is used as the backup power for the watch IC
(IC831) of the FP-152 board, measurement is performed at
the low rate of once every minute to reduce battery
consumption together with the FET switch (Q814).
. Independent operation of FP CPU (IC816)
The power supply circuits are grouped so that the FP CPU
(IC816) can be operated even after the power is turned off.
+3 V, +3.2 V, +5 V-2, +5.3 V, and +12 V are supplied to
the FP-152 board even after the power is turned off. +12 V
-2 or +5 V is not supplied.
. Audio adjustment data storage
When performing automatic adjustment of audio, the
adjustment value is written to EEPROM (IC819). With the
power on, FP CPU (IC816) reads the adjustment value
from EEPROM (IC819) and uses it to correct related
audio.
HDW-F900R/V1 (E)