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How can we use capacitor to build a circuit to generate sawtooth wave

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bhl777

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Hi everyone, I am trying to input two siganls to a comparator, one is a sawtooth wave and another one is a DC level, then we can use the comparator to generate some duty cycle wave. This is how PWM works and I remembered a circuit which used capacitor to generator sawtooth wave by its charge and discharge.
Does anyone know about this kind of circuit and give me the guidance? Thank you very much!
 

You are essentially talking about a opamp circuit with a resistor and capacitor. and a control with a transistor.
 

But if I don't want to use IC on the board to generate sawtooth, is it OK?

kalyanasv said:
You are essentially talking about a opamp circuit with a resistor and capacitor. and a control with a transistor.
Click to expand...
 

you need some sort of amplifier and comparator. You could look into the opamp ic and make a transistor resistor network (opamp) instead of an opamp
IC but that is time consuming and I dont see any great purpose.
 

bhl3302 said:
But if I don't want to use IC on the board to generate sawtooth, is it OK?
Click to expand...

Which devices can you use?... Transistors?
Of course, there will be a need for a sort of a bistable oscillator (made by transistors for example) which also generates a triangular or sawtooth (half triangular) signal.
The comparator might be a simple transistor amplifier, better if it is made as a schmitt trigger type (this needs 2 transistors) to get sharp output edges.

For the sawtooth, I found this:
Sawtooth Generator (Oscillator) with Transistors | Simple Circuit Diagram

Added:
Please note that these transistor oscillators suffer from a relatively high sensitivity to temperature.

Kerim
 
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    bhl777

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UJT relaxation oscillator can be used as a sawtooth generator.
 

UJT relaxation oscillator can be used as a sawtooth generator.
Click to expand...
The transistor circuit linked by KerimF is actually comprised of an UJT simulation circuit and a current source. UJT seems like a kind of legacy these days, some are still available at distributors, e.g. Onsemi 2N6027G.
 

Thank you man, I think KerimF's link is what I am looking for, but I appreciate for your kindest help all the same!

kalyanasv said:
you need some sort of amplifier and comparator. You could look into the opamp ic and make a transistor resistor network (opamp) instead of an opamp
IC but that is time consuming and I dont see any great purpose.
Click to expand...


---------- Post added at 13:29 ---------- Previous post was at 13:27 ----------

KerimF, Yes thank you very much！ This is what exactly I am looking for. I will pay attention to the sensitivity of the temperature!

Best regards,

bhl3302


KerimF said:
Which devices can you use?... Transistors?
Of course, there will be a need for a sort of a bistable oscillator (made by transistors for example) which also generates a triangular or sawtooth (half triangular) signal.
The comparator might be a simple transistor amplifier, better if it is made as a schmitt trigger type (this needs 2 transistors) to get sharp output edges.

For the sawtooth, I found this:
Sawtooth Generator (Oscillator) with Transistors | Simple Circuit Diagram

Added:
Please note that these transistor oscillators suffer from a relatively high sensitivity to temperature.

Kerim
Click to expand...
 

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