Philips B8 Series Service Manual page 18

the Bridge Rectifier circuit. The 160 volts dc goes through T425 to the transistor switch. The
start up signal is taken from the neutral leg of the input ac line.
The Power Supply consists of 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. 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.
The Switching Regulator and the Drive circuits turns the Switch On and Off to allow current flow
through the primary of transformer T425. 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 used as B+ for the
Switching Regulator.
From the secondaries of T425, the voltages needed to operate the television are developed. The
Plus 9 volt output is switched for On/Off control.