Start Up And "Active On" Operation - Sony CPD-420GS Training Manual

Start Up and 'Active On' Operation
The Power Supply uses a flywheel type switch mode supply. It has both
PWM and RCC (Resistor and Capacitor) characteristics. The PWM con-
trols the pulse width of the gate drive. The RCC portion insures that the
next conduction cycle starts at zero volts. Therefore, the gate pulse width
varies and the switching frequency varies.
When Power switch S601 (H Board) is closed, AC (100V - 240V) is ap-
plied to D601 full wave rectifier. +160V DC (110V AC in) is applied through
R603, L604 and R615 to T601/5 (SWITCHING TRANSFORMER). Start
up current is supplied from D601 (half wave rectified), through R613 to
IC601/7 (VCC). Start up voltage at IC601/7 is approximately +12V DC.
IC601/6 PWM
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Once start up voltage is applied, IC601/6 (OUT) outputs PWM drive to the
gate of Q602 (POWER SWITCH). The PWM frequency will vary between
65kHz to 120kHz depending upon input voltage and power level. The
PWM drive from Q602 is applied to T601/2. T601 develops all the sec-
ondary operating voltages. After start up, the output from T601/8 through
R623 is rectified by D605 and provides VCC +17V DC through D624 and
D657 to IC601/7 during normal 'Active On' operation.
Q602/Drain