Part number : STR5412
Function : TV Switch Power Supply
Package : ZIP 5 Pin Type
Manufacturer : Sanken
When the output voltage decreases, the conduction of the STR starts again repeating the cycle already described. However, not all is said, because the source is working at time intervals that may be different from the one corresponding to the horizontal sweep trace, which may cause some instability – pulsating – in the output voltage.
The solution consists, in this case, in synchronizing the operation of the power source, and for this purpose a positive pulse is used extracted from the fly-back transformer, and it is applied to the base circuit of the transistor Q1 via D807 and R805, so that each time the horizontal retrace pulse is present, the conduction of the hybrid STR is initiated, and then it stops doing so once the corresponding working voltage has been obtained. In other words, the STR5412 conducts according to the energy demand demanded by the fly-back, and also, during the recoil, instant in which the brightness of the beam is extinguished on the screen.