Epson DFX-9000 Service Manual page 98

Epson DFX-9000
Overcurrent control
If the +37 V load somehow becomes shorted, the +37 V output is
drooped automatically to prevent the power supply from being
damaged.
Overvoltage control
If an overvoltage occurs on the +37 V output due to a
malfunction of the converter, the status is detected in the
overvoltage detection section, and the +37 V output is shut off
3.3 V Residual Current Circuit
This printer has a circuit that retains 3.3 V for a certain period of time
after the power is off. When the 5 V output has decreased and falls
below the prescribed level after the power has been switched off, this
circuit switches the voltage to a charged electric double layer condenser.
At the same time, the circuit extends the 3.3 V output time by switching
the input voltage for the regulator section where 3.3 V has been
generated, providing a minimum of 50 ms of time to allow data writing
for FRAM and the XOFF response of the serial interface. The following
shows a block diagram of the voltage retaining circuit.
3.3 V
Reset signal
generation
section
5 V
Power supply
POFF signal
board
generation
section
Electric
double layer
condenser
Figure 2-39. 3.3v Retaining Circuit Block Diagram
Operating Principles
XRESET
SoC ASIC
POW_OFF
Mechanical
controller LSI
5 V voltage
switch section
3.3 V
3.3 V
generation
section
Circuit operation
The voltage switching timing is shown below.
+5V
POW_OFF
(BKUP)
+3.3V
XRESET
Figure 2-40. Voltage Switching Timing
Revision B
91