219In the actual circuit, the fixed output voltages are obtained by changing the winding ratio of transformerT100. In this converter circuit, the output voltages are stabilized by controlling the duty cycle of the ONand OFF timing of the transistor. In this power supply, the bias winding is built into the transformer. Thepower supply has four outputs, +24 VDC, -5 VDC, +5 VP and +5 VDC. The +24 VDC output is protectedby the Error Detection Circuit, and the +5VDC, +5 VP and -5 VDC outputs are protected by the circuitryinside of the voltage regulator IC.Control Circuit and Error Detection CircuitThe control circuit amplifies the output of the duty cycle according to the error voltage detected by theError Detection Circuit, and drives the main transistor Q100. The method used to change the duty cycleis to change the ON time period. When the output voltage of the +24 VDC circuit rises, the current ofphoto coupler PC103 increases, the output pulse width of the control circuit decreases and the ON timeperiod of Q100 decreases. This control circuit decides the minimum OFF time period by itself. When theoscillation frequency becomes higher and the OFF time period becomes minimum, the OFF time periodremains unchanged and only the ON time period decreases. This way, there is a upper limit of theoscillation frequency and the duty cycle is expanded.The value of output voltage isEo=d/(1-d)*Eid=Ton/TsEquivalent circuit model for the RCC.Ton : ON time of Q100In the equivalent circuit ; When SW is ON, currentflowsSW LWhen SW is OFF, current flowsL D RLThe value of inductance increase current betweenON period. (d*Ts)IL=Ei/L*d*Ts . . . . . . . . . . . . . . . . . .(1)The value of inductance decrease current betweenOFF period. ((1-d)*Ts) . . . . . . . . . . . . . . . .(2)From equation (1) and (2),E0=d/(1-d)*EiTs : Period of oscillationVLVL L CT100D(D102)EoEoTs dTsRLEiSW(Q100)TILEi(1-d)Ts dTs
