Panasonic TC-26LX20 Technical Manual

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

Panasonic TC-26LX20 Technical Manual Manual pdf 28 page image

enters pin 6 of IC7001 to begin the oscillation. The pulses that aroscillator enter the transformer T7004, causing it to build a magnetic field. The output ofe output at pin 1 of thethe transformer is rectified into 121Vdc and rovided to the LCD panel via the connectorP4. When the rectified output of the transformer reaches 90Vdc, the diodes D7043,D7044, D7045, and D7046 go into conduction, turning on transistor Q7010 and thereby,turning off IC7005. This eliminates the start up voltage of IC7001. The oscillatorcontinues to operate using the run supply created by a secondary of the transformerT7004 and the diode D7014. See Figure 19.Power Off Operation of the DC-to-DC converterWhen the unit is turned off, the 120V_Stop command is provided at pin 2 of theconnector P1/AP10. This causes the transistors Q7008 and Q7009 to turn on and stopthe conduction of IC7005 and IC7006. See Figure 20.The 120V_Stop line is designed to stop the operation of the backlight DC-to-DCconverter if there is a drop or an increase in the 24 volts supply to the AP board. Pin 2of the connector P1/AP10 inputs a High to the P board causing the transistors Q7008and Q7009 to turn on. This causes IC7006 to immediately turn on and short pins 6 and7 of IC7001. This action stops the oscillation of IC7001. To keep the oscillation of the ICfrom starting again, the DC supply is grounded through Q7008.Protection of the DC-to-DC converterOver-current protection of the circuit is provided at pin 7 of the IC7001 from the emitteroutput of Q7018.Over-voltage protection of the primary is provided via the diode D7054. If the rectifiedvoltage of D7018 exceeds the operating voltage of IC7001, the diode D7054 conductsand applies DC to the base of Q7019. The transistor Q7019 turns on and causes Q7018to turn off, effectively removing the feedback voltage to pin 7 of IC7001. This actionstops the operation of the oscillator.p23