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Oscillator circuit is shown.

a) Calculate frequency of oscillations,

b) Calculate minimum value R1 for which circuit still oscillates,

c) Calculate amplitude of voltage VB, for which voltage VA start cuting off

Vz=6.3V, R1=100K, R2=120K, R3=470, R4=2R6=10K, C1=C2=100nF, Vd=0.7V, R4=R5.

I completed task a) and task b)

I got f_oscillations=232.7Hz and R1_min=250k.

I don't know how to solve task c)

Any idea?

Thanks in advance.


1 Answer 1


The begining of VA cutoff would be at the conducting point of the zener pair, equal to (Vz + VD). The gain of OP1 needs to be calculated, (-R5/R4). So the VB needed to reach the cutoff is (Vz + ZD)/(-R5/R4). Feel free to finish the math.

(This assumes that VB is the node to the lower right of label B. This is not 100% clear as there is also a Viz shown there.)


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