In this improved design, pulse-width-controller IC1 derives its power from RT for start-up, auxiliary winding WAUX for normal operation, and shunt-regulator circuit IC2 and Q1 for low-load operation
Figure 3. In this improved design, pulse-width-controller IC1 derives its power from RT for start-up, auxiliary winding WAUX for normal operation, and shunt-regulator circuit IC2 and Q1 for low-load operation