Genius 2093 User Manual
The FET
136
works together with the
transformer
166
to provide a low resistance
current path from V- to GND. This low
resistance coupled with no large voltage times
current products is what makes the power
supply efficient. Resistor
resistance coupled with no large voltage times
current products is what makes the power
supply efficient. Resistor
137
provides a
means for sensing the FET current. In the low
current mode, it is used to set the 300mA current
and in the full on mode it is used to
current mode, it is used to set the 300mA current
and in the full on mode it is used to
The FET drive is always off during the
negative slope of the oscillator, or just after the
sync pulse. Since the FET drive pulse is started
by the error amplifier voltage and terminated by
the end of the oscillator cycle, a control system
via pulse width modulation has been established.
The oscillator waveform is produced by charging
capacitor
negative slope of the oscillator, or just after the
sync pulse. Since the FET drive pulse is started
by the error amplifier voltage and terminated by
the end of the oscillator cycle, a control system
via pulse width modulation has been established.
The oscillator waveform is produced by charging
capacitor
102
with a constant current set by
resistor
J7
to a voltage of 5V and then
discharging the capacitor with double the
charging current to 2.5V. Adding the flyback
pulse, via capacitor
charging current to 2.5V. Adding the flyback
pulse, via capacitor
123
to this waveform
synchronizes the oscillator, since the oscillator
frequency is set below the horizontal frequency.
Resistors
frequency is set below the horizontal frequency.
Resistors
J2
,
J4
and capacitor
108
limit the
error amplifier's AC gain, to hold the control loop
stable. Capacitor
stable. Capacitor
107
holds the error amplifier
stable. Capacitor
110
reduces power supply
noise, but, if too large, will cause the power
supply to be unstable. The 127V line is adjusted
by making solder connections on the J PRA
supply to be unstable. The 127V line is adjusted
by making solder connections on the J PRA
(refer
to page 65 for the layout)
. Solder connections
JC
and
JD
are used to raise the 127V line up to 4.5
volts in steps of 1.5 volts. Connections
JA
and
JB
lower the 127V line as much as 4.5V.
The series regulator IC
115
, controls
current to the monitor GND by pulse width
modulation. A PNP transistor
modulation. A PNP transistor
112
, has an
emitter current, that is directly proportional to
the 127V line voltage due to resistor
the 127V line voltage due to resistor
J1
and
adjustment resistors
J13
&
J14
. This
current is transmitted to the power supply V-
line, and is applied to a resistor
line, and is applied to a resistor
J5
,
J15
, &
J16
. The voltage across these resistors is
compared to a reference voltage by the error
amplifier. If the +127V line goes up the output
of the error amplifier voltage goes up.
The pulse width modulation, which controls the
+ 127V line voltage, is accomplished by turning
the FET drive on at some particular voltage
along the rising slope of the oscillator waveform.
This particular voltage is the error amplifier
output voltage. See waveforms above.
amplifier. If the +127V line goes up the output
of the error amplifier voltage goes up.
The pulse width modulation, which controls the
+ 127V line voltage, is accomplished by turning
the FET drive on at some particular voltage
along the rising slope of the oscillator waveform.
This particular voltage is the error amplifier
output voltage. See waveforms above.
SWITCH MODE POWER SUPPLY CIRCUIT DESCRIPTION.
Oscillator waveform with sync:
FET drive, C5184 pin 10:
Error Amp. V.
Fet Drive
With Sync
Oscillator waveform without sync:
sense the max. current. Resistors
140
,
133
and capacitor
138
reduce power supply
electrical noise. Transistor
127
and diode
116
short the FET drive to V- when the
monitor is turned off to protect the FET from
conducting current with a still large drain
voltage. Resistors
conducting current with a still large drain
voltage. Resistors
J10
,
J11
,
J12
and
134
provide a means for checking flyback diode
142
conduction via a comparator. If the
comparator measures low flyback diode voltage
the FET is turned on to the .3A low current
mode. This mode is necessary for power up,
since initially the +127V line is 0V and no
reverse diode voltage exists. The over voltage
protect circuit, at pin 14, has a trip voltage of
8V and when it is activated, it shuts down the
power supply. The EHT is measured by
rectifying the flyback pulse, with diode
the FET is turned on to the .3A low current
mode. This mode is necessary for power up,
since initially the +127V line is 0V and no
reverse diode voltage exists. The over voltage
protect circuit, at pin 14, has a trip voltage of
8V and when it is activated, it shuts down the
power supply. The EHT is measured by
rectifying the flyback pulse, with diode
130
,
from a secondary winding of the FBT.
Capacitors
Capacitors
125
,
124
and resistors
126
,
J9
are connected as a low pass filter to smooth out
the simulated EHT voltage which is then
applied to the C5184 at pin 14. Resistor
the simulated EHT voltage which is then
applied to the C5184 at pin 14. Resistor
J8
protects the IC current sense input from
voltage spikes and resistor
voltage spikes and resistor
113
protects the
PNP transistor from momentary overvoltage
damage due to line spikes. Zener diode
damage due to line spikes. Zener diode
181
protects the horizontal and video circuits from
overvoltage due to power supply failure. If the
+127V line exceeds 160V, the zener diode
overvoltage due to power supply failure. If the
+127V line exceeds 160V, the zener diode
181
shorts to GND the +127V line.
At the input to the power supply is a
voltage doubler which outputs between 240 to
425VDC depending on the AC line voltage. It
has a three amp fuse
voltage doubler which outputs between 240 to
425VDC depending on the AC line voltage. It
has a three amp fuse
146
to protect the PCB
traces, an inrush current limiter
159
to
protect the rectifier diodes
148
&
156
.
Capacitors
150
and
155
are used to reduce
diode noise from the monitor to the AC input.
For 220VAC operation the voltage doubler is
replaced by a full wave rectifier by adding
diodes
For 220VAC operation the voltage doubler is
replaced by a full wave rectifier by adding
diodes
151
,
154
, capacitors
152
,
153
and
removing the jumper at
152
.
144
&
163
are the raw DC filter capacitors. Resistor
J6
supplies the power supply start current and
resistors
resistors
143A
and
143B
balances the series
connected filter capacitors for 220VAC
operation.
operation.
Caution! When working on a monitor with a
degaussing relay,
degaussing relay,
468
unplug the degaussing coil
to avoid causing the residual current relay to
close on a cold posistor. This can happen if the
24V line is energized by a external power supply.
close on a cold posistor. This can happen if the
24V line is energized by a external power supply.
90
126
J9
125
124
J7
J10
142
J12
134
127
140
138
133
J11
102
J16
J14
J15
J5
137
166
136
J13
115
110
130
107
J2
J4
108
181
J8
113
112
J1
123
116
181
JC
JD
JA
JB
146
159
148
156
155
150
151
154
144
153
152
152
143B
143A
163
J6
468