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KX-MB1520FX7/KX-MB1520FX8/KX-MB1520FXW/KX-MB1530FX7/KX-MB1530FXW
6.19. Power Supply Board Section
This power supply board uses the switching regulator method.
[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 D11-D14 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.
[PWR SAVE mode]
Output voltage of 24V is dropped to approx 10V-14V by making PWR DWN Low.
[Control Circuit and Detecting Circuit]
The control circuit amplifies the output with increased voltage detected in the error detecting circuit.
Then it drives the main transistor.
In this power supply, the duty ratio is defined by changing the ON period of the main transistor.
This is shown as follows.
When the output voltage of the 24V circuit increases, the current of the photo coupler PC1 increases, the pulse width of the out-
put control IC becomes narrower and the ON period of Q1 becomes shorter.
[Over Current Limiter (O.C.L)]
The highest drain current (Q1) is limited by a limit current circuit of the 24V.
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 D576 also prevent over voltage.
Input
Circuit
F1
AC
Input
F2
D11-D14
C5
G
H
+24V
Kick-on
Voltage
Circuit
E
F
HTRCTL
GND
Control
Circuit
R4
R3
R2
Converter
Circuit
5V
Output
Circuit
C
D
+5V
Rectifier
Circuit
A
B
+
Error Detecting
Circuit
O.C.L
Q1
A-B Voltage Wave Form
C-D Voltage Wave Form
E-F
G-H Voltage Wave Form
0
0
0
T1
PC1
IC501
Triac
SCR51
Heat Lamp
PWRDWN
Photo Triac
Coupler PC2
B
lock Diagram
+
-
+
-
Summary of Contents for KX-MB1520FX7
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