Switching Oscillator; Start Up - Normal Mode - Sony CPD-G400 Training Manual

Switching Oscillator

This switching oscillator stage generates seven voltages for the monitor
to operate normally. The stage consist of three major parts:
• Switching Regulator IC603 – Contains an oscillator that runs at 63kHz,
26kHz or at bursts of 18kHz. Duty cycle regulation.
• Power Handling Q605 – A MOSFET can control the high current at
the wide operating frequency of the oscillator.
• Sine Resonate Transformer T602 – Produces the various voltages
required by the monitor.
This monitor's power supply has three operating modes. One mode is
selected depending upon the amount of load. When the load has changed,
measuring the current needed to restabilize the output voltage permits
IC603 to select the same or another operating mode.
Power Supply Operating Modes
Mode Oscillator
Frequency
1. Normal 63kHz
(e.g. bright
screen)
2. Light (e.g. 26kHz
screen
saver)
3. Active off 18.2kHz
6Hz = burst rate
Start Up – Normal Mode
When the front panel power switch is pressed, +170V is applied through
fusible resistor R625 to the switching oscillator stage. This voltage is
evident at the SRT T602 transformer primary windings, Q605/D, and IC603/
pin 1. Oscillation does not start until IC603/pin 14 receives voltage. The
following start up sequence occurs to power the monitor:
Characteristic
Continuous 63kHz oscillator
signal. Duty cycle is changed for
regulation.
Continuous 26kHz oscillator
signal. Duty cycle is changed for
regulation.
18.5msec. bursts of 18.2kHz, 6
times/second.
The 18.2kHz is PWM.
21
1. Switching Regulator IC603/pin 14 receives a voltage above 2.5V.
IC603/pin 14 is labeled OOD for "On/Off Data".
2. Voltage input from IC603/pin 1 is permitted to leave Vaux IC603/pin 6
to charge external capacitor C613 until IC603's oscillator runs. Vaux
is the supply input for the IC like Vcc. C613 must continue to supply
power to the IC until the power supply stage develops voltage to keep
C613 charged.
3. IC603's internal oscillator starts and approximately 65kHz is output
IC603/pin 4.
c h 1 : p k p k = 3 8 6 V
c h 2 : f r e q = 6 2 . 9 k H z
T
1
2
C H 1 1 0 0 V =
C H 2 1 0 . 0 V =
4. This signal is amplified by Q605 and applied to the primary winding of
SRT transformer at T602/pin 5.
5. The SRT transformer has three groups of secondary windings:
• Pins 10-15 supply power to the monitor.
• Pins 16-18 supply voltage to the Horizontal centering circuit.
• Pins 2-3 return a sample of the transformer voltage to IC603.
6. The secondary voltage from T602/pins 2 and 3 are separated into two
paths before fed back to IC603, pins 13 and 7 for control.
• IC603/pin 13 – The R635 path is used to monitor changes to the sec-
ondary load for mode changes between Normal, Light and Active off
operation.
• IC603/pin 7 – The path through D613, R642, D633, and R643 is used
to coarse regulate the output voltage. IC603 uses this information to
change the oscillator pulse width (duty cycle) for output voltage con-
trol. A second regulation path into IC603/pin 9 is used for fine voltage
correction.
M T B 5 . 0 0 u s - 1 . 3 6 d v c h 1 -