What in ***'s name are you trying to do with that poor op amp?
Things to try:
- Sane pin connections.
- Google image search for "Schmitt trigger oscillator".
What are you basing this circuit off of?
That symbol in the yellow image is not an op amp; it is a symbol for an inverting Schmitt trigger (the symbols can be inconsistent though).
The part number 40106 in the other image is **broken link removed**.
A Schmitt trigger is not the same as a Schmitt trigger oscillator; a Schmitt trigger oscillator is an oscillator built using a Schmitt trigger, as shown in the top circuit.
You can create a Schmitt trigger with an op amp comparator, then use that as the core of the oscillators. If multisim has a 40106 or other inverting Schmitt trigger part you can use that as well.
Check out https://en.wikipedia.org/wiki/Schmitt_trigger.
Beware touching the computer screen.This doesn't work so what am I doing wrong here? I am getting -2kV or something similarly utterly rediculous.
Changing the ratio between R8 and R9 should change the duty cycle.But I can't figure out how to alter the duty cycle. Varying the resistor values and capacitor value only alters the frequency.
Hi BoylesgDoes a Schmitt trigger = Scmitt trigger oscillator?
crutschow said:Try using at least a ±10V dual supply.
godfreyl said:Changing the ratio between R8 and R9 should change the duty cycle.
boylesg said:Here is a 741 Schmidtt Trigger but it aint doing what I understand it is supposed to be doing
But I can't figure out how to alter the duty cycle. Varying the resistor values and capacitor value only alters the frequency.
I was referring to the circuit in post 5.Changing resistors will not adjust the duty cycle of the oscillators from post #3.
Exactly, and changing the ratio between R8 and R9 in the circuit in post 5 will do that.To adjust the duty cycle you need to make the Schmitt trigger thresholds asymmetrical.
Yes. For a symmetrical adjustment range (50% +/-x %), we would connect R9 to -Vcc instead of ground.Exactly, and changing the ratio between R8 and R9 in the circuit in post 5 will do that.
LM741 min supply voltage is 10Vpp, a ±5V dual supply will be fine.
Changing resistors will not adjust the duty cycle of the oscillators from post #3.
You'll want a dual supply for the op amp for the Schmitt trigger. +/- 5V will work.
Start by building a Schmitt trigger. The inverting one on wikipedia with R1=R2=10k will work fine. Note the "Vin" and "Vout" labels on the schematic there. Those correspond to the input and output pins of the Schmitt trigger. If you draw a box around it and label Vin and Vout, it might help reduce confusion.
After building the trigger hook up as per the yellow diagram. A 10k resistor and a 10u cap should give you nice results.
This configuration creates a basic relaxation oscillator. In total you will have 1 op amp, 3 resistors, and 1 capacitor.
What is your intention with that function generator?
In the oscillators you posted you cannot adjust the duty cycle by altering resistor or capacitor values. To adjust the duty cycle you need to make the Schmitt trigger thresholds asymmetrical.
For your oscillator you can do this by making the supply voltage to the op amp comparator asymmetrical, e.g. try +6V and -4V, or +5V and -10V.
Alternatively you can build an asymmetrical Schmitt trigger, e.g. **broken link removed**, which is also what you'd want to do if you want it to work with a single supply. This would generally be a better solution than asymmetrical supply voltages.
See https://pcbheaven.com/wikipages/The_Schmitt_Trigger/ for some clarity on the supply and symmetry; and there is an asymmetrical trigger component calculator linked down at the bottom of that page as well.
Note that constructing the inverting Schmitt trigger from wikipedia and then constructing an oscillator from it as per your yellow diagram creates the op amp relaxation oscillator circuit that you see in Falstad.
There's an important lesson there. Opamp spice models are often badly oversimplified which can result in completely unrealistic simulation results.I am getting -2kV or something similarly utterly rediculous.
There's an important lesson there. Opamp spice models are often badly oversimplified which can result in completely unrealistic simulation results.
There's at least three symptoms:
- Output voltage is higher than supply voltage, as you found.
- The circuit works even though you forgot to connect the power supply to the opamp. Duh!
- The current from the opamp's output to the load magically comes from nowhere - there's no current flowing through it's power supply connections.
I just realized not long ago that this circuit contains a schmidtt trigger implemented with discrete transistors. It works really well for 18V under load but how would you modify it to get -18V?
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