Epson Stylus Photo 895 - Process How 42 VDC, 5 VDC and 3.3 VDC Are Generated

EPSON Stylus PHOTO 895/785EPX Revision A
Operating Principles Electrical Circuit Operating Principles 44
Figure 2-18. C408 PSE Board Block Diagram
The C408 PSE board has the various control circuits to stop voltage output if a
malfunction occurs on the power supply board or the main board while the printer
mechanism is on duty. Following explains each control and protection circuit.
2.2.1.1 Process how 42VDC, 5VDC and 3.3VDC are generated
This section provides the description how +42VDC, +5VDC and +3.3VDC are
generated from the supplied power supply referring to the Figure 2-18, "C408 PSE
Board Block Diagram".
1. Regardless of the state of the power switch (On or OFF), the voltage is always
applied to the primary side of the power supply board from the moment or at the
state that AC-plug is plugged in. At this time, F1 plays a role of preventing
AC100V from coming into the F1.
L1 also prevents high harmonic wave noise generated in the RC circuit filter
which consists of C1 from going out, and eliminates the noise from outside here.
2. The AC is full-wave rectified by the diode bridge DB1, and converted to x
AC in voltage by the smoothing electrolytic capacitor C11.
3. The pressured up direct current turns Q1 on through the starting resistor and starts
the primary side of the circuit.
4. When the primary side is On, the energy (current) led by the electromagnetic
induction through the trans (T1) does not flow to the secondary side since the
diode (D51) on the secondary side is installed in the opposite direction.
5. When the energy which is charged in the trans is reaching the saturated state, the
voltage which makes Q1 on becomes weak gradually. At the point that this voltage
drops at the certain voltage, C13 absorbs the current in the opposite direction and
Q1 is quickly shut off by the resulting sharp drop.
6. When the primary side is turned off, the energy charged in the T1 is opened
according to the diode (D51) direction which is installed on the secondary side.
Basically, 42 V DC is output by these circuit operations and the number of T1
spiral coil.
7. +5VDC and +3.3VDC are generated by pressured down this +42VDC as power
supply. The 5V chopper circuit (IC51) and 3.3V chopper circuit (IC151) pressures
down the +42VDC and generates precise +5VDC and +3.3VDC by chopping off
the output, forming the standard sawtooth wave form by the outer RC integration
circuit.
ZC-RCC converter
• Over current protective
function
• Over voltage protective
function
• Secondary side SW
function with delay circuit
• Power saving mode applied
5V Chopper
Circuit
3.3V
Chopper
Circuit
+42VDC
+5VDC
+3.3VDC
PSC signal from
Main board
Energy
EnergyEnergy
Energy saving
signal
Smoothing
Circuit
C51, C52D51
TRANS (T1)
Main Switch
Circuit
Over Current
Protection
Filter Circuit
Full Wave
Rectifier
Circuit
Smoothing
Circuit
C11DB1L1, C1F1, TH1
AC Input
Q1
2