Panasonic KX-FT21BX

KX-FT21LA
- 148 -
10. POWER SUPPLY SWITCHING BOARD SECTION
Block Diagram
[Input Circuit]
The input current goes into the input rectifier circuit through the filter circuit. The filter circuit decreases the noise voltage and
noise electric field strength.
[Rectifier Circuit]
The input current is rectified by D101,D102,D103 and D104 and charge C106 to make DC voltage. Then it supplies power to
the converter circuit.
[Kick-on voltage circuit]
Bias is applied to the Q101 gate via this circuit when the AC power is turned on and Q101 begins operating.
Input
Circuit
AC
Input
Surge
absorber
circuit
G
H
5V
24V
Kick-on
Voltage
Circuit
E
F
GND
Control
Circuit
Over
Current
Circuit
R102
R103
R104
Converter
Circuit
C
D
Over
Voltage
Circuit
8V
Output
Circuit
24V
Output
Circuit
+
-
Rectifier
Circuit
A
B
C106
Error Detecting
Circuit
A-B Voltage Wave Form
0
C-D Voltage Wave Form
0
Voltage Wave Form
0
E-F
G-H
T101
D201
n
2n1
V0V1VIN
IIN
Q101 C201
0t
TOFF TON
VIN
VO
0t
TOFF TON
VIN
VO
n1
n2
Input side
Output side
Input side
Output side
(a) Principle of the RCC method
(b) When the number of transformer windings is one-to-one
(c) When the ratio of the number of transformer windings is n1:n2
Vo is kept constant by varying
the ratio of the time intervals of
T
ON and TOFF.
In Figure (b), different
voltage output can be
obtained by varying the
ratio of the number of
transformer windings.
Load
Vin:TON=Vo:TOFF
n1
n2
Vin:TON= Vo:TOFF
V
[Convertor circuit]
RCC Method of the Constant Voltage Control
Mechanism
Response to Variations in Input Voltage
Figure A(a) illustrates the principle of RCC.
Assuming T
ON while Q101 in the
circuit diagram is ON, and T
OFF while
it is OFF, the voltage generated by the
primary winding can be represented by figures
A(b) and (c).
When the winding ratio is one-to-one, the circuit
functions to make the product of T
ON and the input
voltage constant with the product of T
OFF and the
output voltage.
<Fig. A>