Main 5V Supply - Panasonic LX600 Technical Information

The Main 5V, Main 9V, Sound 20V, and Panel 12V supplies are very similar
in their design and operation. Panasonic utilizes several Buck regulator
circuits to generate these voltages. The primary difference is that the
input voltage to the Main 5V regulator is 10V whereas the 9V, 20V, and
12V supplies use 24V.
1. Operation begins when the Main_On signal, derived from the
TV_Main_On (active low) signal turns off Q7303, providing the "Enable"
for operation of IC7205 on pin 5.
2. The 10V input voltage is switched between pins 1 and 2 at a frequency of
125Khz through the use of an internal oscillator and PWM circuit.
3. When the switch is closed, current flows through coil L7203 causing a
field buildup.
4. When the switch opens, current generated by the field collapses in L7203
and charges the capacitor C7255; D7231 acts as a ground return.
5. Voltage feedback and regulation is accomplished through the use of a
voltage divider, which consists of R7292 and R7293.
6. D7230 prevents peaks generated by L7203 from exceeding 10V and
destroying the IC.
7. Zener diode D7301 monitors the Main 5V output for over voltage and goes
into conduction if the output voltage becomes excessive. Diode D7302
which is reversed biased during normal operation goes into conduction
and trips the AC shutoff circuit.

Main 5V Supply

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