Power Supply Circuit Operation

Figure 2-13 shows a block diagram of the power supply circuit.

The basic constructions of the BOPS and BOPSE units are the same. The figures in parentheses are the current or voltage value, and the lower portions of the rectangles indicate the locations of major elements.

The AC voltage is input to the AC inlet, and is supplied to the power supply board via the POWER switch and fuse. The AC voltage is rectified m Tne 1 voltage doubler rectifier, 1 cnecK! full-wave rectifier), then smoothed by DB 1.

The surge-suppression circuit suppresses the surge current that flows when the printer power is turned on.

The DC voltage is divided into two lines; +35 V and + 5 V, and is converted into the DC voltages required to operate the printer by the RCC switching regulator circuits.

The +35 V line performs DC to DC conversion via T1 and DT1.

The current limiter monitors the current input to . . (total of . to, each current is 4A), and feeds it back to error amplifier 1 r . in .1. The constant voltage controller monitors the voltages input to . and VR 1 (for setting the +35 V line voltage), and feeds it back to 1 (EA1 ).

1 turns the primary switching transistors and _ on and off using the internal transistors and . via transformers T2 and T3.

rii 1 is also equipped with a dead time controller ie buf The entire switching operation can be turned off by setting the dead time to fer. an

In this circuit, four feedback paths can be used for the ina t

One is the feedback from the limiter for each output current from mm. to he D which activates the r-- if an over current is output from the driver circuit. The current limiter mentioned above is used to recover this limiter.

The second is the feedback from the current limiter.

The third is the feedback from the power down signal on the main board. If an error occurs and it is necessary to cut the voltage to prevent the printer from being damaged, the is activated by the PD signal.

The forth is the feedback from the ground level monitor, which activates the | and cuts the voltage to prevent the printer from operating abnormally if the potential difference between the ground (G ND) levels of the +35 V and +5 V lines cause a current of 1A to flow.

The +5 V line performs DC-DC conversion via T4 and DT2.

The current limiter monitors the current flow to R66 and feeds it back to I (comparator).

! ini turns the primary switching transistor -I---on and off via photo coupler PC2.

The constant voltage controller i (shunt regulator) feeds back the voltage fluctuation to |

The V line is also output in parallel from the + 5 V line. When the +5 V line becomes stable, the 12 V line also becomes stable. In this circuit, fuse resistors R7 1 and R72 work as a current limiter.

The constant voltage controller on the 35 V line not only monitors the voltage input to R34 and VR1 (for setting the 35 V line voltage) and feeds it back to20IC 1 (EA1), but also controls output of the CL signal which informs the CPU on the main board that voltage limiting has occurred for the 35 V line. If limiting is executed for the constant voltage controller, (which means the circuit enters the overload state,) comparator IC5A detects it and generates the CL signal.

Upon receiving the CL signal, the CPU on the main board is interrupted, and executes the recovery sequence for the power supply overload state. (Refer to Section 2.3.5.)

The voltage status at the primary side is also monitored by the primary voltage monitor. This is used to generate the switch off (SO) signal which tells whether the printer power is on or off. if the output voltage at the stage just after rectifying and smoothing on the primary side drops to 170 V or less, shunt regulator Q3 detects it and causes the SO signal generator to generate the SO signal via photo coupler PC 1. The SO signal causes a non-maskable interrupt to the CPU on the main board, so that it can write (back up) the data which must be stored in non-volatile memory when the printer power is turned off. (For details, refer to Section 2.3.3.)

The power supply unit has a cooling fan which is driven by the +35 VDC to cool the elements on the circuit board. Since the fan is placed below the carriage motor, it also cools the carriage motor.

2-18

Rectifer

-r power is turned the following da

Inlet 1

Voltage

Double

Rectifier

Smoothing

TT0"

Surge Cut

Gete Voltage

• Parameters set for mechanism control (various iensor status items)

^ A __p-j.______...___X_____l___;________jd; ^ Al PUA BETA ntf \

Line

Line backed up is written to the SRAM when the CPU sets the NMI port to LOW (VP1 —, i the printer povjer is turned off, the SO signal control circ it shown i|n Figure 4-11Fan

W afid generates the chip enable signal to the SRAM (5C

ignal from the power supply ■ LOW when the initialize siç ' the ODtional interface (CN2 " (vel ( ' '

t 3 jpply circuit monit terminal vc____ae of the SRAM to tt i mis way, the backup data is stored in vel on the +5 V line drops.

eeWDrLYevaePC

Monitor (1A)

joard.

al (INIT: Low active) is input fr p nn thfi + 5 V line, and s\

kup circuit, and Table 2-16 gi\

SO signal (To Mai.

Main

Switching J OIUIVH

L

1

Constant

Final

Smoothing

Secondly

Secondly

Smoothing

-

(2A)

08,09

R?

5V Line

Constant

Figure 2-13. Power Supply Section Block Diagram

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