Samsung ER-220 Service Manual

4.CIRCUITRY4-1 POWER CIRCUITThis machine has two different power sources, the one is a powercircuit and the other is a BATTERY.The power circuit generates five different DC voltage sources, +5Vfor the logic, +17¥ for the printer driving, +4V and -24V for the displayand +11.2V for the power fail detection circuit.The BATTERY applies +3.6V to the back-up circuit.A. VPP(+17V)The VPP voltage is used for the source voltage of the printer drivecircuit. The AC 18V is rectified by the BRIDGE DIODE RECTIFIER BD1 andit is regulared by the capacitor 50V 2200uF.The switching circuit composes circuit of 2 Transistors KSC945 andKSD288,a zener diode 18V, to maintain the output voltage at DC 17V.B. VPF(+11.2V)The VPF voltage is used for the input voltage of the power faildetection and reset circuit.The AC9.5V is rectified by the BRIDGE DIODE RECTIFIER BD2 andregulated by the capacitor 35V 10uF. Then the output is +11.2V.C. VCC(+5V)The VCC is used for the power source of the system logic.The most part of this voltage, rectified by the BD2 and passedthrough the diode 1N4003 , is regulated by the capacitor 35V 2200uF,and it input the 3 - terminal regulating IC MC7805. Then output voltageis applied to directly to the logic and other +5V terminal.1N4003 VFa VFKVDI+OZ24vSOVI0OUFsi680DGND1N4003OCTE: <\PFRees “ GESs tri BV 100UEaees,“apane Los rr 1K-1WSincea Mav (a) ae2200UF