Xerox WorkCentre XK50cx Service Manual

Also see for WorkCentre XK50cx: User guide

4-5-3 Power CircuitINPUTThis product is equipped with a three-wiregrounding-type power inlet. Insulation is class 1.When a power device part breaks down or sometrouble in this circuit causes a short, excess currentruns through a fuse and blows it to protect powerdevices and the system from excess current andprevent a fire.Input filter of power input terminal removes linenoise flown in from outside and reduces noise whichis made in power circuit and logic part andconducted or radiated through power cords.AC input voltage is rectified by bridge diode of fullwave rectifier, is converted to DC voltage bysmoothing circuit, and switches the power device ofthis voltage.As switching is in RCC(Ringing Choke Converter)mode, switching frequency changes from about50KHz to 100KHz.PWM(Pulse Width Modulation) Control Circuitadjusts the duty of the switching device by sensingthe change of output voltage, and protects thisproduct from excess current by receiving signalsfrom excess current detecting circuit.DRIVING CIRCUIT (START-UP CIRCUIT)If you insert a power plug into AC outlet, full-waverectified DC output voltage is generated at inputelectrolysis condenser and supplied to the gate of aswitching device through driving resistance. Thisvoltage drives the switching device. Once it isdriven, it continues to switch via PWM controlcircuit with power supplied by auxiliary coil Nb.SWITCHING CIRCUIT (VOLTAGESTABILIZATION)12V of 2nd voltage is detected by voltage detectorand feeds back through photo coupler to 1st PWMControl Circuit signals compared by error amplifier.PWM Control Circuit controls the gate of powertransistor according to the feedback voltage so as tosupply load with stable output voltage.OCP CIRCUIT (OVER CURRENTPROTECTIVE CIRCUIT)If a short in secondary load terminal or a short insidepower device causes excess current, powerconsumption increases. Then it increases current ofpower transistor.The current of power transistor increases linearlywhen it is on. This current is detected by sensingresistance and is impressed to excess voltageprotective circuit of PWM control circuit through RCintegration circuit where over current protection isbuilt in.If this voltage becomes bigger than Vbe of excesscurrent control transistor, the potential of powertransistor gate falls immediately and it stops drivingpower transistor to protect it from excess current.OVP CIRCUIT (OVER VOLTAGEPROTECTIVE CIRCUIT)If the main power of power device 12V increasesabnormally, this excess voltage is detected by OVPdetecting circuit and 12V output terminal shifts to astate similar to a short.If 12V output terminal shorts, over current runs onover current detecting terminal and OCP circuitoperates to prevent a fire in power device.4-28Circuit