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Panasonic Z-421V Technical Manual Manual pdf 37 page image

Panasonic Z-421V Technical Manual

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Contents
  1. Table Of Contents
  2. S MALL SIGNAL PART
  3. Sound
  4. Horizontal and vertical synchronization
  5. Luminance and chrominance signal processing
  6. Color Decoder
  7. AFC - Tuning - ATS
  8. D IGITAL CONTROL SIGNALS
  9. H ORIZONTAL DEFLECTION - FBT
  10. V ERTICAL DEFLECTION
  11. Drive circuit part
  12. V IDEO AMPLIFIER AND ABS
  13. ABS operation
  14. Beam current limiter
  15. Euro-scart
  16. P OWER SUPPLY STR-S5707
  17. Latch Circuit
  18. VCR PART
  19. RECORD AND PLAYBACK PROCESSING CIRCUIT
  20. PLAYBACK PROCESSING
  21. AUDIO SIGNAL PROCESSING (LA71511M)
Panasonic Z-421V Technical Manual Manual pdf 37 page image
3DQDVRQLF371.6 Power supply STR-S57071.6.1 Vin terminal, start-up circuitA start-up circuit is to start and stop a operation of a control IC by detecting a voltage appearing at aVin terminal (pin 9). At start up of a power supply, when a voltage at the Vin terminal reaches to 8V(typical) by charging up C817 by the function of a start-up resistor, R804, a control circuit startsoperating by the function of the start-up circuit. After the control circuit starts its operation, powersource is obtained by smoothing voltage appearing at winding of pin 6,7 of T801.1.6.2 Oscillator, F/B terminal voltage (pin 7)A oscillator generates pulse signals which turns a power transistor on and off by making use of chargeand discharge of C1 and C2 incorporated in the Hybrid IC. Constant voltage control of a switch-modepower supply is performed by changing both on-time and off-time except when the load is light (ex.remote control stand-by mode of TVs). The on-time is controlled by changing a current charged byC1, which is as the result of that the detection winding of pin 5-7 of T801, which detects a change ofvoltage in a secondary side, connected to the sensing terminal (pin 7). has the current in accordancewith an output signal from an output voltage detection circuit (an error amplifier) built in. As an ACinput voltage to the power supply gets the higher and a load current the smaller, the current flowing tothe SENS terminal gets the larger, and the on-time gets the shorter.1.6.3 Function of INH terminal (pin 6), control of off-timeSignal to the INH terminal is used as inputs to COMP.1 and COMP.2 inside of the control IC. Athreshold voltage of COMP.1,VTH1 is set at 0.75V(Ta=25°) and an input signal to a drive circuitbecomes almost 0V (the power transistor is in OFF mode) when a voltage at the INH terminal reachesthe VTH1. A threshold voltage of COMP.2, VTH2, is set at 1.5V (Ta=25°). When the INH terminalvoltage reaches VTH2, an output from COMP.2 reverses (the power TR is in on mode).* Quasi-resonant operationBy inputting the voltage of winding of pin 6-7 of T801 which is synchronized with the energy dischargetime of a secondary winding to the INH terminal through D810 and R808, quasi-resonant operationcan be achieved.When the power transistor turns off and a voltage higher than VTH2 is applied to the INH terminal,C3immediately discharges and then starts charging again. Even after the discharge of energy of asecondary winding is completed, VINH does not immediately increases. when it gets lower than VTH1,the transistor turns on.1.6.4 Drive circuitThe STR-S5707 applies the proportional drive system in order to minimize turn-on and saturation loss,and storage time.1.6.5 OCP functionOver-current protection is performed pulse by pulse by directly detecting collector current of the powertransistor. detecting voltage is set to -1V below a reference point of GND (ground).
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