Philips 13PT30L1 Service Manual page 64

E8 CHASSIS POWER SUPPLY BLOCK
When a 120Vac source is connected to the E8 chassis, approximately 160Vdc is developed by the bridge
rectifier circuit. The 160 volts dc goes through 5545 to the FET switch. The start voltage for the switching
mode power supply is taken from the hot leg of the input ac.
The power supply includes a single integrated circuit, operating as a free-running switching mode power
supply. The frequency of operation varies with the circuit load. There is no separate power supply for
standby; instead, the power supply turns On when ac is applied. The switching regulator IC starts switching
when the initial voltage is applied through the start circuit. Inside the switching regulator, the drive circuit
turns the FET switch On and Off to allow current to flow through the primary of the transformer 5545. Energy
stored in the primary during the On-time is delivered to the secondaries during the Off-time. Feedback from
the Hot secondary is used to control the switching regulator. Positive voltage from the hot secondary is
rectified to provide B+ for the switching regulator. The voltages needed to operate the television are
developed from the secondaries of 5545.