61
Converter 2
Converter 1 and Converter 2 stages are similar. The only differences are
how they first power up and what voltages they deliver to the TV.
After the AC power relay is energized, Converter 2 receives a kick-start
voltage from Q5005. R5073 limits the amount of current through Q5005
to start Converter 2’s oscillator. Once the converter is running, one output
voltage line (D5037) sustains the Vb operating voltage. The higher con-
verter voltage reverse biases the kick-start diode D5014, blocking the kick-
start voltage from transistor Q5005.
Converter Operation Sequence
There are several parts to the converter stage. They are listed in the order
of operation:
Converter Stage Parts
Name / Major
Components
Inputs
Output
Purpose
Kick start
Q5005
Current limited
+164V from
R5073
+12V through
blocking
D5014 to
IC5004/pin 12
Starts the IC5004
converter
oscillator and
supply IC5003.
Driver/Osc
Control
IC5004
Vcc - pin 12
Freq. control -
pin 6
Out of phase
63.4kHz
square wave –
pins 9 and 10
Oscillator
Freq. control
Driver
Amplifier /
Driver
IC5003
Logic supply
voltage – pin 9.
Output supply
voltage – pins 3
and 6.
Complementary
inputs 12Vp-p –
pins 10 and 12.
Gate drive
output – pins 7
and 1.
Outputs in phase
with inputs.
Level shifting for
top MOSFET
Q5012.
Output
MOSFETs
Q5012 &
Q5013
12Vp-p drive
signals from
IC5003/pins 1
and 7.
150Vp-p
square wave
63.4kHz @
Q5012/Source
Transformer
T5003
286Vp-p rough
sine wave @
T5003/pin 8
Multiple
secondary
voltages
Ground isolation.
Provide various
TV voltages.
IC5008,
PH5003,
D5024,
D5030
+5V source
from D5041.
Reduction of
voltages at
IC5004/pins 1
and 6.
Converter 2
regulation using
+5V output as
fdbk.
Kick Start
When switched AC is applied to D5514, unreg164V is applied to
the converter MOSFETS Q5012 in Converter 2 and Q5005. Kick-start
transistor Q5005 regulates this voltage to +12 using zener D5018. Q5005
is current limited by a low wattage R5073 at its collector. Q5005 is not
designed to run continuously.
Oscillator/Driver/Output
When IC5004 receives this start voltage at pin 12, its internal oscillator
runs and a square wave is output to driver IC5003. IC5003 provides suffi-
cient current to drive the two output MOSFETs, Q5012 and Q5013. These
MOSFETs feed Converter 2’s T5003, which outputs various TV operating
voltages.
Kick-start Cutoff
One output from T5003/pin 10 is rectified and feeds +13 volts back to
power the converter logic IC5003/pins 3 and 9 and IC5004/pin 12. The
higher voltage also back biases D5014, shutting off the initial kick-start
supply voltage from Q5505/emitter.
The waveforms show the input (ch 1) and outputs at Driver IC5003 (ch 2
and 3). The waveforms were taken with a scope connected to hot ground
and the TV connected to an isolation transformer.
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