Panasonic KX-F1200 Service Manual And Technical Manual page 144

KX-F1200 I
The circuit in the pluvlous page, whun the Lransistor Q101 is ON, secondary rectifier diode D201 is OFF and the energy is
charged in the transformer T101. Q101 continues being ON while the voltage is generated by control winding (B). Q101 is
tuned OFF by control circuit, then each windings of T101 changes the polarity and rectifier diode D201 truns ON.
The charged energy of T101 supplies power through D201 to output load. And the voltage of control winding is decreased
and Q101contines being OFF state. When all energy is discharged through D201, Q101 is turned ON again and it makes the
polarity of each windings of T101 in reverse and goes to self oscillation. When input voltage Ei is high, the ON period of Q 101
becomes shorter, and when load current is high, the ON period of Q101 becomes longer.
The value of output voltage is
Eo = d/(1-d)*Ei
d = Ton/Ts
Ton:
ON TIME OF Q101
T, : PERIOD OF OSCILLATION
In the equivalent circuit:
When SW is ON, current flows
SW-* L
When SW is OFF, Current flows
L-* D-_ RL
The value of inductance rectifiers increasing
current during ON period.
IL = Ei / L*d*Ts (1)
The value of inductance rectifiers decreasing
current during OFF period.
IL = Eo/L(1-d) * Ts (2)
From equations (1) and (2),
Eo = d/(I-d) * Ei
i
,= =!_dTs.
(1 -d)Ts
In the actual circuit, the fixed output voltage can be obtained by changing the winding ration of transformer T101. In this con-
verter circuit, the duty ratio of ON period and OFF period of the transistor produces output. In this power supply, the bias
winding is also built-in in the transformer and the output value is one. 24V output voltage is stabilized and changes the duty
ratio.
[Control Circuit And Error Detecting Circuit]
The control circuit amplifies the outputwith increasedvoltagedetected in the error detecting circuit, then drives the main tran-
sistor.In this power supply the duty ratioisdefined by changingthe ON periodof maintransistor.
This is shownas follows.
When the outputvoltageof 24V circuitbecomeshigher,the currentof photocouplerPC10t increases,the pulsewidthof out-
put controlIC becomes narrowand the ON periodofQ101 becomesshorter.
[Over Current Limiter (O.C.L.)]
IC101 rectifiers the highest voltage with resistors R105 and R113 detecting the current in the primary side. When the current
is supplied higher than the highest voltage, it switches to ratch mode which stops oscillating.
[DC-DC converter]
Output 5V, +12V, -12V are made by T201,Q202 and DC-DC Converter. 5V output is rectified by D207, Q204, Q205 and
Q203. +12V and -12 V definethe voltagewiththe windingratioof transformer.
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