Tektronix 494AP service manual 105, Theory of Operation- 494l4g4Ap Servlce,Vot, Oenanon*l

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o							Theory of Operation- 494[l4g4Ap Servlce,Vot. 1
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o			TRIGGERIN (PIN 2I				lm-
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o							CONTIOL VOLTAGE		= 6.6
o							tt(v1(
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o		f =140k.95 pF
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o		F		.,o*.,P oR AFIERCuRRENT.,,.,__I			o"enanon*l
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a									2727-161
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o					Flgure7-35.Tirningwaveformsfor soft-startclrcuit
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o	Inverter Driver. The inverter driver consists of						and minimumloaded output. At minimumduty cycle,
o	transistorsQ6072and e6079, transformer
					T60g1,		each transistor is off for approximately6 ps,or 4O;/oot
	relatedcomponents.This is a push-pull amplifierand
o	diodeprotectionin the collector					with	the total period.
	age frornvoltagetransients				circuitsto pr€ventdam,
o	signal is inducedinto.the			duringoperation.The drive
				two slcondary wlndingsof
	T6081andcoupted
o		to the outputstage.
o							Soft'Startand Prlmary Over-CurrentClrcuits. The
o	^ 9utput Stage. This circuit consists of transistors						soft-startcircuit consists of U6053and associatedcom-
							ponents. Soft-start gradually
a	Q.2071and Q2061,series LG tank L10g1/C1063,								increasesthe switching
							transistofs duty cycle at turn-onor after over-current
						and
	transformerT4071. The output transistors are con-						shutdown prevent
O	nected in a half-bridgeconfiguration.						to	excessive
									translstorcurrentdueto
					The two transis-		chargingoutput capacitors. R€fer to Figure 7-35 for
o	tors drive the series tank, which acts as an energy						timingwaveforms.
	storage element and..an averaging circuit. Outp-ul
o	transfonnerT4071is drivenby tne tanf circuit,anctit, in
	turn, drivesthe secondarycircuits.
o	Primaryregulation,-as						The primary over-currentcircuit protects against
o			discussedpreviously,				secondary shorts that		could destroy the switching
	when the duty cycleof the inverter					occurs
							transistors. T2080 s€nses the collector current in
	ing transistors				driver mainswitch_
o		is varied.Maximum					Q2071and createsa vottageon pin 5 of U60468. lf the
					duty cycleoccursat
	low input line (90V) and fulty toadedoutput. At max-						bias on pin 5 surpassesthe 2.5 V referenceon pin 6, at
a	imumdutycycle,both
	the period,	transistbrsare off for only				1Ao/oof	approximately 6 A	through e2OT1, the output of
		or l.Sps.
o			This short intervalallbws any				U60468sets U6063A. U6063Ais a D-typeflipflop used
	stored base chargeto deplete,so there is no chance						as a timer to shut down the inverterlogic for approxi-
o	both transistors will conduct at the same time.						matety1 s andto resetthe soft-startcircuit.
	Minimumduty cycteoccursat high input tine (132V)
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o									7-105

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