High Voltage; Hv Manufacture; Hv Regulation - Sony CPD-G400 Training Manual

High Voltage

Overview
The purpose of this stage is to use the horizontal drive signal to manufac-
ture high voltage. High voltage is used in various areas.
High Voltage Usage
Voltage
27kV CRT screen
accelerating
Focus (about 4kV) CRT Focus
1kV CRT G2 accelerating
300V Vertical dynamic
focus output circuit
This stage consists of a HV manufacturing part and a regulating part. The
regulating part keeps the HV constant when there are changes in bright-
ness.

HV Manufacture

HV Control IC901 makes two signals from the horizontal drive signal input
pin 14:
• Fixed drive signal from IC901/pin 5
• PWM signal from IC901/pin 3
Fixed Drive Signal
IC901 takes the horizontal drive signal that is input pin 14 and makes a
positive going signal (9.6usec. in the aging mode). The width is a function
of the input horizontal frequency. This positive going signal outputs IC901/
pin 5 and is used to turn ON and OFF (drive) HV Output MOSFET Q902.
MOSFETs are often used in monitors because they have an even gain for
a large frequency range.
Q902 amplifies the drive signal and the signal from the Drain is applied to
the flyback's primary winding. The flyback's secondary windings produce
the various high voltages needed by the monitor.
Purpose Where
CRT anode
CRT socket
CRT socket/D board
Q706, D board
57
PWM Signal
The PWM signal from IC901/pin 3 is used to control the high voltage from
the T901 flyback transformer. IC901's PWM output directly controls the
conduction time of switching MOSFET Q901. A LOW going pulse applied
to its gate turns on Q901. When Q901 is turned ON, voltage is applied
through T902 to HV Output transistor Q902/Drain to serve as B+. The
longer Q901 is turned ON, the higher the B+ voltage is at Q902. As
Q902"s B+ increases, so does its gain and the T901 flyback voltage (HV).
1
2
T
3
C H 1 1 0 . 0 V =
C H 2 1 0 . 0 V = B W L
C H 3 ! 1 0 . 0 V = A L T M T B 2 . 0 0 u s - 0 . 2 0 d v c h 3 -
IC901 Waveforms
Name
Channel 1 H Drive input
Channel 2 PWM Output
Channel 3 MMV Output
Time base
* The pulse widths will be different when sync is input the monitor.

HV Regulation

HV regulation is accomplished by controlling the B+ applied to Output
MOSFET Q902/Drain. This is done using IC901 and Q901 in a closed
loop regulation system. IC901 samples the flyback output voltage at T901/
pin 17. This voltage is returned to IC901/pin 11 for comparison to a 9V
reference at pin 12. The LOW going pulse that is output IC901/pin 3 is
changed in width based upon this comparison. A wider LOW going pulse
Aging Mode *
Location Voltage/div
IC901/pin 14 10Vp-p
IC901/pin 3 10Vp-p
IC901/pin 5 10Vp-p
2usec/div