3. +35 V Constant Voltage Control Circuit
The +35 V constant voltage control circuit is illustrated below.
The constant voltage control circuit operates to keep the 35 V line at 35 V
±
6 %. When the voltage between
ZD51 and ZD85 becomes 32.7 V
±
2.75 %, PC1 turns on, and then Q2 also turns on. Consequently, switching
FET Q1 shuts off. When the voltage between ZD51 and ZD85 becomes less than 32.7
±
2.75 V, PC1 turns
off, and then Q2 also turns off. Consequently, switching FET Q1 operates again. Repeating the above
operation keeps the +35 V line at 35 V
±
6%.
4. +35V Line Overload Detection Circuit
The +35 V line voltage drop protection circuit is shown in the figure below.
When the +35 V line is overloaded, it means that constant voltage control is not being maintained. In this
condition, the forward current of PC1 drops to 0 A. Consequently, voltage Vf between PC1 and D81 also
drops. On this circuit, when the Vf voltage drops below 1.3 V (+35 V line: 33.1 V), IC528 detects the
overload and outputs the PWDN signal (+5 V: HIGH active) to port 20 of the CPU. When the CPU receives
this PWDN signal, printing stops. When the +35 V line becomes normal again, the voltage between PC1 and
D81 also becomes normal. When the Vf voltage goes above 1.6 V (+35 V line: 33.4 V), the PWDN signal is
removed.
+35V Line
ZD81
ZD51
ZD82
ZD83
ZD84
ZD85
D81
R56
R57
GND Line
9+
10+
11
R11
C13
Q3
R14
C12
+
Q1
1
2
8
7
R20
R21
R19
C15
Q2
R13
R15
R16
IC1
Figure 2-25 +35 V Line Constant Voltage Control Circuit
+35V Line
ZD81
ZD51
ZD82
ZD83
ZD84
ZD85
D81
R56
R57
GND Line
1
2
8
7
PWDN
+5V Line
GND
R87
R86
R83
R84
+
-
7
8
4
6
5
PC1
Q31
R20
Figure 2-26 +35 V Line Overload Detection Circuit
LQ-2070 Service Manual
Operating Principles
Rev.A
2-19
Содержание 2070 - LQ B/W Dot-matrix Printer
Страница 1: ...EPSON TERMINAL PRINTER LQ 2070 SERVICE MANUAL EPSON 4006244 ...
Страница 5: ...REVISION SHEET Revision Issued Date Revision Page Rev A April 8 1996 1st issued ...
Страница 11: ...Product Description LQ 2070 Service Manual Figure 1 1 Exterior View of the LQ 2070 1 2 Rev A ...
Страница 55: ...LQ 2070 Service Manual Operating Principles Rev A 2 7 ...
Страница 58: ...Operation Principles LQ 2070 Servcie Manual 2 10 Rev A ...
Страница 63: ...Down LQ 2070 Service Manual Operating Principles Rev A 2 15 ...
Страница 112: ...Disassembly and Assembly LQ 2070 Service Manual 3 34 Rev A ...
Страница 146: ...Maintenance LQ 2070 Service Manual 6 4 Rev A ...
Страница 165: ...EPSON ...