Sony TVP-08, Training Manual

Page: 109 / 139

101
HV Regulation PWM
Overview
The purpose of the HV Regulation PWM is to create a sawtooth wave-
form using the H Drive pulses. This sawtooth will be used to create a
PWM waveform by comparing it to the output of the HV Regulation Con-
trol circuit. This PWM signal will be used to control Q8008 PWM HV
Regulator.
Sawtooth Generator
The H Drive signal is input to Q8009/B. Q8009 is a buffer whose output is
from the emitter. The signal is next input to Q8010/B, which inverts the
signal and outputs it from the collector. R8044, C8026 and C8029 also
integrate the signal at this time.
This signal is then compared to a reference voltage by IC8002. IC8002/
2 is a reference voltage of 9 volts. The result of this comparison is output
at IC8002/1. The signal is then integrated again by C8045 and input to
Q8018/B. This signal is inverted and shaped by Q8018 and output from
its collector as the following pulse:
This pulse is input to Q8022/B. When the signal is LOW, Q8022 is OFF,
thus allowing IC8008 to act as an integrator. This causes the output at
IC8008/7 to rise gradually because C8066 is in the feedback path of
IC8008. The output rises like a sawtooth and is applied to IC8002/6 through
R8096. The output continues to rise until the pulse at Q8022/B becomes
HIGH. When this occurs, C8066 is short-circuited by the C-E junction of
Q8022, causing IC8008 to become a buffer. This causes the peak signal
of the signal to be passed through D8023 directly to IC8002/6. This places
a pulse on the end of the sawtooth during Horizontal retrace time. This
cycle continues with the input of the pulses to Q8022/B
PWM
IC8002 PWM creates a PWM signal by comparing the sawtooth signal
with the output from the HV Regulator Control circuit whose output comes
from IC8007/1. When the Sawtooth signal input at IC8007/6 is greater
than the input at IC8002/5, it will cause IC8002/7 to output a LOW. When
the sawtooth is less than the regulator input, IC8002/7 will output a HIGH.
This PWM /-12 volts to be output at the emitters of Q8015 and
Q8016. This signal will be output Q8008 to regulate the High Voltage.
Q8009/B
2V 20us
Q8010/C
2V 20us
Q8018/B
5V 20us Q8022/B
2V 20us
IC8008/6
1V 20us
IC8002/6
2V 20us