Panasonic KX-FT21BX Service Manual page 12

KX-FT21BX/KX-FT21BX-W
E
1
Gate signal
T T
ON OFF
T=1/f= fixing
T + T =T
ON OFF
The following is an overview of how the power supply unit is controlled.
The control method of this power supply unit is pulse width modulation.
When Q is ON, the energy is charged in the transfer primary coil according to E
1
When Q is OFF, the energy is output from the secondary transfer as follows.
1
L ? D1 ? Load ? L
Then the power is supplied to the Load. When Q
The output voltage is fed back in the control IC according to the error amp rectifier.
Then depending on how T
Also, when the current load becomes too large, in order to decrease the voltage output, the increase
in is controlled and the output voltage is stabilized.
Therefore, basically the timing: Ton/Toff of Q1 controls the output voltage.
Coil width value
Primary of the ratio
I
IN
n
Q
1
Control IC
is controlled, stabilization occurs.
ON
Output/Input voltage value of ratio
light load
V /E
0 1
4
3
2
1
0
0 0.5
= Duty ratio
T
on
=
T
(Model KX-FT21BX/KX-FT21BX-W)
-12-
Secondary
: n D
1 2
E
2
L
Error amp rectifier
is ON, power is not output from the secondary side.
1
heavy load
increases
1.0
1
V
0
V
R
.
1
24V
Load