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AP3302 Pt3 Contents

AP3302 Pt3 Section 2Contents

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AP 3302 Pt. 3

Section 2


Square Waves applied to CR circuits

J. F to G. C commences to charge. VC starts at +23.5V so that the effective charging voltage applied to it is 100 - 23.5 = 76.5V. In time CR (100 us) Vc therefore rises exponentially from +23.5V to 23.5 + (63/100 x 76.5) = + 71.5V. VR falls from + 76.5V to + 28.5V in the same time (VC + VR = 100V at this instant).

The process continues after G until the circuit reaches a state where C is charging and discharging by equal amounts on alternate half cycles of the input. After a few cycles VC settles down about a mean value of +50V and VR about a mean value of zero volts. The shaded areas in the waveforms of Fig 9b are equal, indicating that the variations about the mean, levels for both VC and VR are the same.

Long CR Circuit

Let us assume that a symmetrical square wave of voltage, of amplitude 100V and pulse duration 100 us, is applied to a CR circuit where C = 0.001 uF and R = 2 MW (Fig l0a).


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