Sub 9V And 30V Tuner Supply - Panasonic LX600 Technical Information

SUB 9V and 30V Tuner Supply

The SUB 9V and BT 30V Tuner sources are generated by the same switch
mode power supply IC, IC7209.
The supply encompasses the design of both Buck and Boost regulator
circuits.
1. A soft-on enable is provided on pin 5 of IC7209 during the initial power on
sequence as capacitor C7294 charges.
2. The 24V input is switched between pins one and two at a frequency of
125Khz.
3. The operation of the 9V supply is similar to that of the 5V supply.
4. D7602 is responsible for supplying the 9V to the capacitors when the
magnetic field within the coil collapses.
5. When the switch contact is open, the A side of coil L7204 goes negative,
providing a reference for the capacitors C7601, C7610, and C7609 to
charge to 9V via the diode D7602.
6. The next time the switch is closed, the 24V appears at the A side of the
coil causing the same capacitors to charge to 24V. As a result the 24V
and 9V charges add up, resulting in the 30V output.
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