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CACD Group updated 2000.03.30 Author Janez Puhan |
Three Phase GeneratorThe circuitAn oscillator consists of two sections, an active element and a feedback network. Together they form a closed loop. When disconnecting this loop and injecting a test signal, both the input and output signals around the loop are uniform in phase and magnitude at the resonant frequency. If the loop gain drops below unity, then oscillation of the closed loop would decay exponentially. If the gain exceeds unity, then the loop gain would be limited to unity due to clipping nonlinearities. This effect can be observed with the following example. Three cascaded RC circuits and inverters form a closed loop system. Conditions for oscillation are satisfied when the phase lag of the RC circuits equals 60 degrees. At nodes (2), (4) and (6), three phase-lagged sine waves are produced and may be used as control signals for three phase power inverters. The input file (three_phase_generator.cir)three phase generator * fo = 1 / (2 pi r c 3^(1/2)) .control tran 0.05ms 10ms uic plot v(2) v(4) v(6) xlabel t[s] ylabel output[V] title 'TRAN analysis' .endc x1 1 2 invertor x2 3 4 invertor x3 5 6 invertor r1 6 1 100k r2 2 3 100k r3 4 5 100k c1 1 0 10n ic=0 c2 3 0 10n ic=7.5V c3 5 0 10n ic=15V .subckt invertor 1 2 v0 4 0 dc 15V r1 1 3 100k r2 2 3 820k m1 2 3 4 4 pmos m2 2 3 0 0 nmos .ends .model pmos pmos .model nmos nmos .end The results |
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