Vdcline Regulatorcircuk; Vdcline Regulatorcircuti - Epson C117001-N - DFX 5000+ B/W Dot-matrix Printer Service Manual

Operating Principles
2.2.2 +5
The
+5
The rectified and smoothed DC voltage turns on the +5 VDC line first. RIM is a starting resistor.
When the +35 VDC line becomes +13 V, switching regulator IC TL494 (IC151) creates a +5 V line.
The power supply board uses a 2-step rise method. When the printer is turned on, the +35 VDC
line outputs +13 VDC for 140 ms. The first rising voltage (+13 VDC) is used to check the printhead
drivers on the C117 MAIN board assembly.
to the power supply board. When the power supply board receives this signal, the photo-coupler is
turned on and it cuts off the voltage of the primary side. This prevents printhead damage when a
rises to +35 VDC after 140 ms.
If the +5 VDC line exceeds +7 VDC, the current flows to ZD153. Then Q155 is turned on, the
common circuit with the DRERR signal feedback circuit on the C117 MAIN board assembly.
comparator is used for over-voltage control. Pin 16 (+12) monitors the +5 VDC line. If this voltage
exceeds +5 V (pin 15), internal comparator 1 outputs a HIGH signal. The other comparator controls
the +5 V Iine over-current. Pin 1 (+11) monitors the current of the +5 V line. If the current exceeds
the set value (pin 2), the voltage becomes HIGH and comparator 2 outputs a HIGH signal.
Both the comparator 1 signal and comparator 2 signal are tied by the wired OR. If the output signal
is HIGH from either comparator, the output signal is HIGH. This switching procedure monitors the
Cl and C2 ports. These switching waveforms are controlled by PWM (Pulse Width Modulation),
which changes the level of the inverse terminal of comparator 1 and comparator 2.
This circuit prevents printhead damage when a printhead driver is damaged. When the printer is
turned on, the C117 MAIN board assembly tells the C117 power supply board assembly whether
the printhead drivers are normal.
If a printhead driver is damaged, the C117 MAIN board assembly sends the DRERR signal to the
signal, it stops creating +35 VDC and +5 VDC. If the printhead drivers are normal, the C117 MAIN
board assembIy sends the VPC signal to the C117 power supply board assembly. When the C117
power supply board assembly receives this signal, it creates +35 VDC.
2-14
C2 cl
1
Figure 2-15. +5 VDC Line Regulator Circuit
HZS7B-2
Rev. A