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Section 6
Circuit Description
6-1. PS-613 Board
The PS-613 board is a DC/DC converter board that generates the power supply to the CA-46 board.
For the generated voltage, a CAM12 V voltage is generated as the voltage used on the camera circuit
board.
The generated voltage is used as a circuit voltage of _7.5 V and 15 V supplied to CCD and as +3.3 V,
+3.3 V (HDRV), +2.5 V, and PELTIRE+CCD cooling drive power supplies.
IC201 (MB3785A) uses a 46-pin SQFP-type IC package to realize a switching regulator controller.
IC201 has a four-channel internal controller. IC201 generates a voltage by using this internal controller.
6-1-1. Switching regulator functions
Reference voltage circuit
The reference voltage circuit uses the temperature-compensated reference voltage (2.5 V) generated by
the power supplied from pin 18 (power pin) of IC201 as an operating power supply inside IC. It can also
output the reference voltage from pin 19 of IC201 to the outside as a Vref signal.
Chopping wave generator circuit
The chopping wave generator circuit generates an arbitrary chopping wave oscillation waveform by
connecting a timing capacitor (C204) and resistor (R206) to pins 17 and 16 of IC201, respectively. The
amplitude of this waveform is 1.3 V to 1.9 V. The chopping wave is input to the PWM converter inside
IC201 to drive each channel.
Error amplifier
The error amplifier detects the output voltage of a switching regulator and outputs a PWM control signal.
It has a wide in-phase input range and can facilitate the voltage setting. The error amplifier also sets the
gain and voltage arbitrarily by connecting a feedback resistor and capacitor from the output pin of the
error amplifier to the inversion input pin.
PWM converter
Channels 1 and 2 are a voltage comparator that has two inversion input pins. They are a voltage-to-pulse
converter that controls the ON time of an output pulse according to the input voltage.
Channels 3 and 4 are a voltage comparator that has one inversion input pin. They are a voltage-to-pulse
converter that controls the ON time of an output pulse according to the input voltage.
An output transistor can be turned on while a chopping wave oscillation waveform is lower than an
amplifier output signal and DTC signal. The output current is 30 mA (maximum).
Channel control function
IC201 can independently control a four-channel power supply circuit. However, the DXC-S500 is
designed so that the circuit output is obtained when the voltage level is high with pins 20, 21, and 22 of
IC201 connected. This time, the voltage level is always in the high-level state.
6-1
DXC-S500 (E)
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