Sony Cyber-shot PRO DSC-D700, Service Manual

Page: 107 / 116

4-19 DSC-D700 (UC,CE)
4-10. FUNCTION DESCRIPTION OF RM-177 BOARD
The RM-177 board is a DC/DC converter board that produces the power for the
system board and 2.5-inch liquid-crystal display board of a DSC-D700 digital still
camera. The RM-177 board also mounts the photosensor of an infrared unit.
A voltage is produced as the UNREG2 voltage used on the system control circuit
board and liquid-crystal display board.
The operating voltage is used as _ 7.5 V, 15 V and 4.5 V for liquid-crystal display.
These voltages are used as the driving power.
These powers are turned on and off from the system control board using a PWRC
(SY) signal. Each power is not adjusted and controlled in the operating voltage
range.
The concrete functional operation is described below.
IC652 (MB3785A) employs a 46-pin, SQFP-type IC package for the switching
regulator controller operation. IC652 has a 4-channel internal controller. Using all
functions, IC652 produces the voltage described above.
1. Switching regulator functions
1) Reference voltage circuit
The reference voltage circuit generates a temperature-compensated reference
voltage (2.5 V) by the power supplied from the power pin (pin 18) and uses it
as the internal operating power of IC. The reference voltage can also be sent
out from pin 19 to the outside as a signal at the Vref pin.
2) Chopping wave generator circuit
This circuit generates an arbitrary chopping oscillation waveform by
connecting a capacitor and resistor for timing to pins 17 and 16. The
amplitude of this waveform is 1.3 to 1.9 V. The waveform is input to the
PWM converter in IC to drive each channel.
3) Error amplifier
The error amplifier detects the output voltage of a switching regulator and
outputs a PWM control signal. The in-phase input range is wide and the
voltage can be set easily. Moreover, the gain and voltage can be freely set by
connecting a feedback resistor and capacitor from the output pin of the error
amplifier to the inverting input pin.
4) PWM converter
Channels 1 and 2 have two inverting input pins. The PWM converter is a
voltage-to-pulse converter that controls the ON time of an output pulse
according to the input voltage using a voltage comparator.
Channels 3 and 4 have one inverting input pin. The PWM converter is a
voltage-to-pulse converter that controls the ON time of an output pulse
according to the input voltage using a voltage comparator.
An output transistor is turned on while a chopping wave is lower in level than
the output signal of an amplifier and the signal at the DCT pin. The
maximum output current is 30 mA.