P Board - Primary Power - Panasonic TC-26LX20 Technical Manual

P Board - Primary Power

The Primary power supply is responsible for generating the following:
1. The standby power supply
2. The primary source voltage (14volts) for the secondary power supply.
3. Backlighting voltage (15 Volts) for the TC-22LR30
STANDBY POWER Circuit
The incoming AC voltage passes through the inrush current resistor R7001 and enters
the rectifier circuit consisting of D7015, D7022, D7023, and D7024 for conversion to
DC. The output is then applied to IC7005, a 7volt regulator. The 7volt output of the
regulator is sent to the AP board for conversion into 3.3V. This 3.3V is provided to the
DG board via pin 44 of the connector PAP2 to serve as standby voltage for the system
control circuit.
14V POWER SUPPLY
When a power up command is sent by the system control IC (Main Micro IC1106 on the
DG board), the AC_ON pin 47(connector PAP4 pin 13) sends a high to transistors
Q7002 and Q7003 to activate the power relay RL7001. AC passes through the relay
and enters the bridge rectifier consisting of D7005, D7007, D7008, and D7011.
The diodes convert the AC voltage into DC, which is then applied to pin 3 of IC7003 via
the transformer T7001. The voltage on pin 3 of this IC causes it to oscillate and output
a PWM pulse to drive the transformer T7001. As a result, energy is built and released
from the transformer.
The AC output at pin 11 and 14 of the transformer is rectified into 14 volts to serve as
the primary source for all other voltages. After the power supply starts running, the Run
Supply for IC7003 is supplied by diode D7033 connected to pin 8 of a secondary
winding of T7001. AC voltage from pin 8 of the transformer is also rectified by D7034
and applied to a switching control (regulator) circuit consisting of Q7005. Output of the
switching control IC is tied to pin 4 of IC7003 where it is monitored for over voltage
conditions. Voltage regulation is achieved via the 14V Error Detection circuit, which
consists of IC7006 and IC7008. The output of IC7006 is connected to pin 1 of IC7003,
the same input as the Run Supply.
15V POWER SUPPLY
This circuit generates +15Vdc used on the AP board. This voltage is also used to power
up the DC to AC converter for the backlight of the LCD Panel. The switched 14Volts
(sw+14V., which is generated when the unit is powered up), in conjunction with the
MAIN_ON_ACT (signal (H): approx.3.0V), allows Q7001 to turn on and activate the
Relay (RL7002). The rest of the operation is exactly the same as that of the 14 Volts
power supply.
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