17
PH601 is an opto-isolator. Pins 1 and 2 are connected to the +135 volt
line and to IC602/2 Error Amp. These pins are the terminals of an LED.
Variations in the +135 volt line effect how much light is output from the
LED. Pins 3 and 4 of PH601 are the emitter and collector of the internal
phototransistor. The brighter the light from the LED, the more current can
flow through the C-E junction. When there is conduction, C-E voltage
from IC601/4 VIN is applied to IC601/1 OCP/FB through R644. This DC
voltage helps regulate the supply by changing the DC level of the signal
created by the quasi-resonant operation. Changing the DC level alters
the ON/OFF time of the internal FET. This in turn changes the frequency
of operation. By controlling the frequency, the power transfer is con-
trolled between the primary and secondary windings of T603. This regu-
lates the supply’s output, which means regulation is maintained by fre-
quency control.
The table below shows the typical operating frequency checked at IC601/
3, and the IC601/1 voltage under maximum (white raster) and minimum
(black raster) loads.
+135
Frequency
IC601/1 DC Voltage
White Raster
135.6 DCV
145kHz
1.71 VDC
Black Raster
136 DCV
200kHz
1.6 VDC
OSC.
UVLO
OVP
TSD
LATCH
1
3
4
5
FDBK
OCP
2
Vin
OV
E
R
-CURR
E
N
T
& FEED
BAC
K
S
O
URCE
DRA
IN
SU
PPL
Y
GROUND
IC601
IC601 Internal Protection
IC601 has three protection circuits. They are over voltage, over current
and thermal protection.
OVP
The over voltage protection circuit functions by monitoring the voltage
present at IC601/4 VIN. If this voltage rises above 22.5 volts, the switch-
ing circuit will be stopped. This OVP activates a latch circuit and power
must be disconnected for operation to restart.
OCP
Over current protection is done by monitoring the voltage at IC601/1 OCP/
FB. IC601/1 OCP/FB only operates during the turn ON portion of the FET
switching. If the voltage passes over the threshold during this time, switch-
ing will stop. This will cause the voltage at IC601/4 VIN to fall below the
voltage needed to operate the IC. This voltage will rise above the operat-
ing threshold on the next positive half cycle of the AC input and cause the
FET in IC601 to turn ON. If OCP is detected again by IC601/1, the cycle
4 VOLTS
~
~
FET OFF
TRANSIENT
~
~
.73
DC LEVEL CONTROLLED
BY PH601
FET ON
IC601/1
Summary of Contents for FD TRINITRON WEGA KV-13FM12
Page 27: ...22 NOTES ...
Page 48: ...APPENDIX ...
