Panasonic TC-26LX20 Technical Manual

Also see for Combo TC-22LR30: Operating instructions Service manual

Panasonic TC-26LX20 Technical Manual Manual pdf 26 page image

Standby Power SupplyThe standby power supply provides the necessary DC voltage to the system controlMicroprocessor, the Reset circuit and the EEPROM. A.C. voltage is supplied to the FullWave rectifier (D7025, D7026, D7031, D7030), through the Line Filter and TransformerT7004. The 7volts standby voltage produced by the rectifier is present as long as theunit is plugged in.The 7volts output passes through the AP board and enters the DG board where it isregulated to 3.3V and fed to the system control circuit. Although the unit is plugged intothe wall outlet, the main power switch located on the front face of the unit must be in theON position for the unit to enter and remain in the standby mode.Primary Power SupplyWhen the system control circuit obtains a power up command from the operator, theAC_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 forrectification into 24 volts DC where it activates the relay control circuits Q7013 andQ7014 to activate relay RL7002. The DC level is then boosted to 380Vdc by the PowerFactor Control (PFC) circuit, IC7002. The power factor control circuit is made up of anoscillator used to control the charge and discharge time of the transformer T7001. Startup 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 areswitched ON/OFF to allow the charge and discharge of the transformer T7001. Thecharge of T7001 is added to the rectified voltage of D7002 to create 380V. IC7002 alsooutputs a PWM output that turns the transistor Q7007 on and off to control the chargeand discharge time of the transformer T secondary output of the transformeris rectified to 24Vdc and supplies the AP board. The diode D7017 rectifies the ACoutput of on Runoutput is monitored via IC7008 and IC7003 for voltagegulation. The output of this power supply is also monitored for excessive voltage bys7002. Thee of the secondary windings of the transformer T7002 to serve asSupply for IC7002. The 24VdcreD7022 and IC7004. If the output rises to 30 volts or more, the zener diode D7022 goeinto conduction, causing the photo-coupler to conduct and stop the operation of IC7002.21