Technology of Q 2500 colour TV set

Technology of Q 2500 colour TV setIt is conceivable that the essentially higheremitter currents (IE max. = 4.5 A) will invokeenormous "flooding" of charge carriers in theN-P- and P-N-transitions of the semiconductor.In order to guarantee rapid switchingbehaviour and to ensure rapid dischargeof the charge carriers in the base zone, thebase control is correspondingly low resistance.32“/16:9/RF c.r.t.s, 142V at 21,24,28“/4:3 and136 V for all other c.r.t.s. The exact controland switching rhythm during a line period correspondsto the principle of the switchedresonant circuit. For this the line switchingtransistor operates via its three operating conditions- conduction, inverse conduction andblocked – in such a way that the charge anddischarge procedures of the collector capacityC 531 and inductivity T 531 determine theexact trace and flyback intervals.Screen+ II Abl.0- I+UU CE0- UTrace1st partInverseoperationTrace2nd partNormaloperationSwitchingtransistortOnly during the horizontal flyback time isQ 534 blocked for 6 µs. By charging the operatingvoltage the capacitor of the parallel resonancecircuit C 531 forms the positive halfwave of a sinusoidal oscillation. C 531 andT 531 are dimensioned in such a way thatthey create horizontal flyback pulses. Thenatural desire of a parallel resonance circuit toconvert the stored charge in the capacitor intoinductance as magnetic energy leads to reversalof polarity of the current.Normally the negative component of the sinosoidaloscillation is felt on the collector ofQ 534. This attempt is however prevented bythe collector-base diode path of Q 534.On reaching the start up voltage the diodepath becomes conductive and cuts the negativecomponents. In these cases the E/Wmodulator diodes support this function,whereby in the switching transistor the powerdissipation of the transistors is reducedIn this respect it must be mentioned that thecontrol pulses are specially formed for thedual functionality of Q 534 normal and inverseoperation. In principle the trace relationship ofthe base control of 6 µs flyback and 26 µstrace time is changed to 14 µs flyback and18 µs trace time. In this way it is possible, toprocess unavoidable production dispersion ofthe driver transformer. By means of promptcontrol the switching transistor has sufficienttime to prepare for the following operationalphase.The horizontal deflection pulses are detacheddirectly from the collector of the switchingtransistor on the parallel deflection winding.Between the base point of the horizontal deflectorand the E/W diode modulator theeast/west correction information is coupled inaccordance with the dual generator principle.This procedure is almost non-reactive withrespect to the primary winding of the highvoltage transducer.The operating voltage of the horizontal outputstage is taken from the switch mode powersupply and is 146 V for 33“/4:3 andDocument Q 2500 24 © Loewe ProCollege