Samsung DVD-R155 Service Manual page 103

Circuit Operating Descriptions
1) F/B terminal of PQIZ1 determines output duty cyle.
2) C-E (Collector-Emitter) of PQIZ1 and F/B potential of PQIZ1 are same.
13-1-3 Internal Block Diagram (Internal Block Diagram of S.M.P.S. Circuit)
Fig. 13-4
Samsung Electronics 13-3