Samsung RM255BASB, RM255BABB manual Power Bus, Circuit Descriptions, and a voltage proportional to

Circuit Descriptions

12-1) POWER BUS

This POWER BUS, and SMPS (Switch Mode Power Supply), is an improved efficiency power- convertion circuit for converting AC input voltage to high voltage DC. However, a consistent attention should be paid to the POWER BUS because 115V AC and 170V DC may be generated. The voltage input has AC applied into BD1(Rectifier Circuit) through FUSE(F1) and LF1, and smoothes the rectified voltage through C101(180uF/450V). As a result, DC voltage is applied into the SMPS TRANS. At the same time, the rectified DC voltage is applied into No 2. of U5(TOP246Y)08 through R24 and R25, and starts initial IC operation. With the role of SNUBBER Circuit (D1, R18, C7, TVS1, C8), also controls the switching wave-formed P-P voltage to protect U5 IC. R21(2W470K) is the parts that special regard must be paid to the safety against potential electric shock during SVC, which is charged with power ON and discharging electricity with power OFF. When the initial operating voltage is applied into U5 No.2 PIN, the U5 IC starts high speed (130KHz) switching operation. And then the input voltage is applied into NP1 (primary winding) of TRANS first,

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