Philips 20PT643F Service Manual page 100

Figure: Internal block diagram of the driver IC (TEA1507)
Introduction
The supply is a Switching Mode Power Supply (SMPS). The frequency of operation
varies with the circuit load. This 'Quasi-Resonant Flyback' behavior has some important
benefits compared to a 'hard switching' fixed frequency Flyback converter. The
efficiency can be improved up to 90%, which results in lower power consumption.
Moreover, the supply runs cooler and safety is enhanced.
The power supply starts operating when a DC voltage goes from the rectifier bridge via
T5520, R3532 to pin 8. The operating voltage for the driver circuit is also taken from the
'hot' side of this transformer.
The switching regulator IC 7520 starts switching the FET 'on' and 'off', to control the
current flow through the primary winding of transformer 5520. The energy stored in the
primary winding during the 'on' time is delivered to the secondary windings during the
'off' time.