Standby Power Supply (Figure 2)
The Standby Power Supply produces a +5 Volt Standby and a +12 volt Standby supplies This is a
Pulse Width type switching power supply Power is applied to this circuit when power is applied to
the unit This Supply is located on the Pre-Conditioner panel When Power is first applied to the
circuit, the internal switch in 7500 applies a charging voltage to 2504, which is connected to Pin 4
When 2504 charges to 5 7 volts, the internal switch switches to internal Capacitor 2504 is now
supplying power to the PWM The internal switch then drives the internal FET to drive transformer
5500 7500 continues to drive the transformer until 2504 discharges to 4 7 volts Capacitor 2504
is again charged and the cycle is then repeated When the secondary 5 volt supply reaches the
correct voltage, 7502 is turned on, driving the opto-isolator 7501 Voltage from the Hot secondary is
rectified by 6503 and applied to 7501 Voltage from 7501 then keeps 2504 charged to 5 7 volts An
internal Zener Diode, inside 7500, keeps the voltage at 5 7 volts Regulation is accomplished via
the shut regulator 7502, opto-isolator 7501, and the internal current sensing resistor in 7500 If the
5 volt supply increases, the shunt regulator drives 7501 harder causing an increased voltage drop
across the internal sensing resistor Rs inside 7500 The PWM will then reduce the On time in the
internal FET, reducing the output voltage
POWER ON CIRCUIT
When the mechanical On/Off switch is turned On, the 5 volts Standby voltage is switched to the
+5VSTBYSW-REL and +5VSTBYSW lines (Figure 3) When the Power is turned On via the Remote
Control, Pin 1 of the Microprocessor, 7001, goes Low This switches 7370 Off The Supply On line
then goes High via the +5VSTBYSW line If one of the Shutdown circuits is activated, 7371 is
turned On which turns 7370 On, turning the set Off
The +5VSTBYSW and Supply On lines are fed to the Line Conditioner panel (Figure 4) There is a
two stage turn On to supply power to the Line Conditioner circuit When the Supply On line goes
High, 7681 turns On, switching relay 5680 On Capacitor 2683 provides a short delay for the turn
On of 7684 and 7690 which turns relay 5690 On The Line Conditioner circuit provides 380 volts dc
to the VS-VA Power Supplies
The VS and VA supplies are Frequency controlled supplies (Figure 5) The output transformer,
5002, and related components form a Resonant circuit As the Frequency of the supply approaches
the resonant frequency of the output circuit, the output voltage increases When the unit is turned
On, 380 volts dc form the Line Conditioner circuit is applied to the switching FET, 7005 A Startup
voltage is applied to Pin 15 of 7001 The Variable Frequency Oscillator drives transformer 5001
which drives the output switches, 7005 and 7006 A Feedback Error voltage from the secondary
controls the Variable Frequency Oscillator to control the Output voltage The Fault Detect latch is
activated if a problem is detected on the secondary The VA Supply is identical to the VS supply
The VS supply outputs a 180 volts supply for the Plasma Panel (Figure 6) Secondary voltage on
Pins 13 and 12 of 5002 is rectified by 6020 to produce the 180 volt supply Feedback for the Error
Amplifier to regulate the supply is accomplished by sampling the 180 volt supply and by a feedback
Vrs signal from the Plasma Panel The 180 volt supply is sampled by 3024, 3025, and 3026 The
sampled voltage feeds shunt regulator 7010 which drives the opto-isolator 7002 Feedback voltage
from the Plasma Display feeds shunt regulator 7011, which also drives 7010 The Feedback circuit
is powered by voltage from Pin 14 of 5002
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