Epson Stylus Pro 5000 Service Manual page 64

Stylus Pro5000
[Various Protection Circuits]
Each output power source from *1 through *4 numbered in the figure2-29
has protection circuit, as it is explained below.
*1) 5 VDC Stabilization Circuit
IC51(L4960), which is also HIC for drop circuit, outputs +5 VDC, as +42 V
line power supply voltage. If the switching circuit on the primary side gets
shorted by any malfunctions, the output voltage level on the secondary
side gradually increases and may damage C228 main board and C228
DRV board. Therefore, +5 V output line is always monitored by ZD94, and
output will be stopped completely, if the voltage level exceeds 9 VDC.
*2) +42 VDC Line Stabilization Circuit
+42 V consists of 2 stabilization circuits. It is the control circuit to vary the
On/Off timing of the switching circuit located on the primary side by 7
Zener diodes, which are from ZD51 to ZD86 on the circuit. If +42V lines
falls to +38V by the influence of overloading, electromagnetic induction on
the primary side is encouraged to be stopped periodically by turning the
main switching FET(Q1) off. This circuit is called constant voltage control
circuit.
The other one is the over voltage protection circuit. If the voltage of +42 V
line falls into the abnormal situations, especially assuming the malfunction
on the switching circuit on the primary side, this protection circuit stops all
the operations on the C228 PSB board so that the abnormally increased
voltage is not output. This circuit is called the over voltage protection
circuit.
*3) +28 VDC Line Stabilization Circuit
This circuit is mounted on the same line as the +42 V line over voltage
protection circuit is on, which is mentioned above. It stops all the
operations on the C228 PSB board, when +28V line falls to the abnormal
situations by malfunctions of the switching circuit on the primary side, etc.,
and the voltage level exceeds 33V. This circuit is also called over voltage
protection circuit.
Rev.A
*4) Delay Circuit
Since the power supply switch is on the secondary side, even if the power
is turned off on the control panel, the exclusive power off sequence still
operates. Following shows various power off sequences, which are always
performed, when the power is turned off from the control panel.
T
Closing ink valve
T
Carriage lock set
T
Paper eject operation(if the printer is still printing)
T
ASF load paper system reset (If it is operating)
Chapter2 Operating Principles
2-25