Power Supply Board Section - Panasonic KX-MB771GR Service Manual

KX-MB771GR

6.18. POWER SUPPLY BOARD SECTION

The power supply board circuit generates +7V and +24Vdc. It also supplies
AC voltage to the halogen heat lamp in the fuser unit.
The power supply board uses the switching regulator method.
AC
Input
Input
Circuit
A-B Voltage Wave Form
0
C-D Voltage Wave Form
0
E-F
G-H Voltage Wave Form
0
Heat Lamp
[Input Circuit]
The input current goes into the input rectifier circuit through the filter circuit.
The filter circuit decreases the noise voltage and the noise electric field strength.
[Rectifier Circuit]
The input circuit is rectified by D10 to D13 and charge C5 to make DC voltage.
Then it supplies power to the converter circuit.
[Kick-on Voltage Circuit]
Bias is applied to the Q1 gate via this circuit when the AC power is turned on and Q1 begins operating.
[Over Current Limiter (O.C.L)]
The highest drain current of Q1 is limited by a limit current circuit. The 24V output is limited by this circuit.
[Over Voltage Circuit]
If the 24V output increases because the error detecting circuit or control circuit is broken, Control circuit will recognize this signal
and output becomes 0V. D104 and D503 also prevent over voltage.
Dummy load method (to quickly check the power supply output)
Refer to POWER SUPPLY BOARD SECTION (P.174).
Block Diagram
A
Rectifier
+
Circuit
Kick-on
C5
B
Voltage
Circuit
R2
R3
R4
Triac
SCR51
T1
Converter
Circuit
C
Q1
D
Control
Circuit
E
O.C.L
F
Error Detecting
Circuit
PC1
Photo Triac
Coupler PC2
62
G
24V
+
7V
+
GND
H
HTRCTL