Panasonic DX-2000 Service Manual page 267

Main Switching Circuit
In the above circuit, when the main switching transistor, Q101, is turned On, input voltage, Ei, is supplied to the primary winding
of transformer T101. However, no current will flow through diode D201 of the secondary side, due to reverse polarity of the
secondary winding causing no current flow within T1. But the transformer charges with energy. When Q101 is turned Off, the
supply voltage to the primary winding shuts off and the windings of T101 change polarity, allowing D201 to conduct, releasing
the energy accumulated in T101 to the circuit. When the energy is discharged through D201, Q101 turns on, once again
reversing the polarity on T101 windings, creating a self-oscillation circuit.
he value of output voltage is
o=d/(1-d)*Ei
=Ton/Ts
quivalent circuit model for the RCC.
SW
Ei
(Q101)
VL
VL
Ts
In the actual circuit, the fixed output voltages are obtained by changing the winding ratio of transformer T101. In this converter
circuit, the output voltages are stabilized by controlling the duty cycle of the ON and OFF timing of the transistor. In this power
supply, the bias winding is built into the transformer. The power supply has four outputs, +24 VDC, -12 VDC, +5 VP and +5 VDC.
The +24 VDC output is protected by the Error Detection Circuit, and the +5 VP and -12 VDC outputs are protected by the
circuitry inside of the voltage regulator IC, +5 VDC is protected by ZD251.
D(D201)
Eo
L C
T101
Ei
Eo
dTs
IL
(1-d)Ts dTs
Ton : On time of Q101
Ts : 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 increase current between
RL
on period. (d*Ts)
IL=Ei/L*d*Ts . . . . . . . . . . . . . . . . . .(1)
The value of inductance decrease current between
off period. ((1-d)*Ts) . . . . . . . . . . . . . . . .(2)
From equation (1) and (2),
Eo=d/(1-d)*Ei
T
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