Yes, I think so; it depends on exactly what they meant by threshold. The use of the singular "threshold" in the question is why I suggested finding the singular astable input voltage. But speaking practically, it is going to swing to one rail or the other and resetting it would reguire the inverting input to cross above the upper threshold or below the lower threshold - depending on whether Vo was at +3 or -3V respectively.DGElder,
So to confirm does that answer the Ops original question "Calculate the threshold voltage for the circuit. Assume the maximum output voltage swing of the op-amp is ± 3 V for when the supply is ± 5 V"
i.e. Threshold voltage is 0V and 3V?
Please keep in mind that this is dieggo3's thread and that we ask that people not just solve other people's homework.WBhan thanks for the help.
My course notes show that Vthresh= Vsupply (R2 / R1+R2)
which would equate to V thresh = 3 x 0.5 which would give 1.5V.
However they have thrown a additional 3 V power supply into the original question on the bottom of the Voltage Divider (which is not covered in any of the notes).
So with my calculations When the output of the amp is +3v we will get 0V on V+ of the Amp
and when Output is -3V we will drop 3v across each resistor (both 1K) giving us 3V on V+ to the Amp
Therefore a upper and lower threshold of 3V and 0v
I have run the circuit through Pspice in Simetrix and come up with a graph showing the thresholds at 3v and 0V
Just really after a bit of confirmation I am on the right track....otherwise I am slowly losing the plot and have somehow managed to get Spice simulation to conveniently lie to me (being the first time i have used spice)
Cheers in adavnce
They are somewhat close, but you need to show some work for us to be able to figure out where you are going wrong.I have done some workout, and I came with answers:
Upper threshold voltage is 4 V
Lower threshold voltage -1 V
Is it close to the right answers ?
Thanks
How do you get that "Vsat" is 5 V? Read the information you provided in the original post: "Assume the maximum output voltage swing of the op-amp is ± 3 V"Vsat=5. V4=3
UTP=((Vsat-V4)xR2/R1+R2)+V4=((5-3)x1/1+1)+3=4
UTP=((-Vsat-V4)xR2/R1+R2)+V4=((-5-3)x1/2)+3=-1
Yep! Do you see how showing your work let us zoom in immediately on what your problem was?I hope I'm getting on the right track this time,. so. Vsat=3
Then I get UTP=3
and. LTP=0
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