LG MW-30LZ10 Service Manual - Page 14

3-1. Explanation of Circuit Movement If the AC Input voltage(1) is confirmed to power device, this Input voltage is adjusted as DC wave form through EMI FILTER(2) and the first adjusting part(3). This adjusted wave form is input to PFC(4, Power Factor Correction) and makes the PFC circuit works and the output voltage(+390Vdc) by PFC circuit becomes a Main Input voltage of MAIN(5), STANBY(10) Switching part. Input voltage is input to Switching part(5, 10) and make this High voltage DC voltage(390Vdc) to be a High Voltage spherical wave with high frequency through the Switching by the elements such as FET, PWM IC. To keep the secondary adjusted voltage to be regular and safe in changing Input voltage and Output load, the output voltage is watched and feedback to switching part(5, 10) through the control circuit(9). BLOCK 2 works as Forward converter method by receiving Input of BLOCK 1 and supplies MAIN DC(+24V, +12V) voltage and the Step Down circuit(8) supplies +18V. Also, BLOCK 3 works as Flyback converter method by receiving Input of BLOCK 1 and supplies +5V for Stanby. Protection circuit is built in switching part(5, 10) to protect over electric-current, short, over voltage of the secondary output. This circuit protects the output and stick the Terminal Switch(15) to radiator while PFC and protect a fire or other accident by turning the AC voltage off while overheating. To minimize power consumption, if the OFF signal is transmitted to PFC part(4), Main part(5) through the control circuit connected from Main board to Power board, only the +5V circuit for Standby works and others are OFF. - 14 -