Standby Power Supply; Primary Power Supply - Panasonic TC-26LX20 Technical Manual

Standby Power Supply

The standby power supply provides the necessary DC voltage to the system control
Microprocessor, the Reset circuit and the EEPROM. A.C. voltage is supplied to the Full
Wave rectifier (D7025, D7026, D7031, D7030), through the Line Filter and Transformer
T7004. The 7volts standby voltage produced by the rectifier is present as long as the
unit is plugged in.
The 7volts output passes through the AP board and enters the DG board where it is
regulated to 3.3V and fed to the system control circuit. Although the unit is plugged into
the wall outlet, the main power switch located on the front face of the unit must be in the
ON position for the unit to enter and remain in the standby mode.

Primary Power Supply

When the system control circuit obtains a power up command from the operator, the
AC_ON pin of the MPU, IC1105, outputs a high to the relay control circuits Q7011,
Q7012, Q7015 & Q7016 to activate the relay RL7001. The AC voltage enters D7002 for
rectification into 24 volts DC where it activates the relay control circuits Q7013 and
Q7014 to activate relay RL7002. The DC level is then boosted to 380Vdc by the Power
Factor Control (PFC) circuit, IC7002. The power factor control circuit is made up of an
oscillator used to control the charge and discharge time of the transformer T7001. Start
up voltage for the circuit is obtained at the output of the D7002.
As the PWM pulses are output from IC7002, the transistors Q7003 and Q7004 are
switched ON/OFF to allow the charge and discharge of the transformer T7001. The
charge of T7001 is added to the rectified voltage of D7002 to create 380V. IC7002 also
outputs a PWM output that turns the transistor Q7007 on and off to control the charge
and discharge time of the transformer T
is rectified to 24Vdc and supplies the AP board. The diode D7017 rectifies the AC
output of on e of the secondary windings of the transformer T7002 to serve as
Supply for IC7002. The 24Vdc
re gulation. The output of this power supply is also monitored for excessive voltage by
D7022 and IC7004. If the output rises to 30 volts or more, the zener diode D7022 goe
into conduction, causing the photo-coupler to conduct and stop the operation of IC7002.
7002. The
output is monitored via IC7008 and IC7003 for voltage
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secondary output of the transformer
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