I want to design a pulse generator. IC's are forbidden. The desire is: Frequency must be 355 Hz to 3 KHz. Duty must be %10 to %50.It is my circuit.

Thread Starter

ahmetkara4635

Joined May 5, 2024
12
I could have stated it better, you are right. Opamps are not banned, integrated devices such as NE555 that will simplify the issue are banned. Yes, this is my project assignment. I could not find a solution for how the frequency changes as the duty changes. Also, there is an inverting opamp at the end of my circuit, which I put for gain, but the circuits that work more or less separately do not work when combined.
 

BobTPH

Joined Jun 5, 2013
9,300
simplest way would be to look at the design of the NE555 and duplicate it with comparators and a discrete SR flip flop.
 

Thread Starter

ahmetkara4635

Joined May 5, 2024
12
I read your post. I wrote " integrated devices such as NE555 that will simplify the issue are banned" And the title including IC's are banned. How can I make a 555 without using logic gates. I am new in the forum. And it's my first post. You are right .I wasn't clear enough
 

dl324

Joined Mar 30, 2015
17,157
there is an inverting opamp at the end of my circuit, which I put for gain, but the circuits that work more or less separately do not work when combined.
Post a schematic.

There are numerous opamp/comparator application notes that show how to make a PWM circuit. Search for information on PWM, oscillators, integrators, and/or comparators.
 

crutschow

Joined Mar 14, 2008
34,855
So IC op amps are okay, but all other IC's are banned?

If you search for PWM circuit using op amps, you should find many hits.
 

WBahn

Joined Mar 31, 2012
30,303
You shouldn't have to find someone else's solution somewhere so that you can copy it and turn it in as your own. Even if that is allowed, it is robbing you of the majority of learning that this project is (hopefully) intended to offer.

You should be able to design a circuit that does this, based on an understanding of how basic circuits work.

Your specs aren't clear in the sense that it isn't clear whether you need to design a circuit in which the frequency and duty cycle are adjustable, or whether you can just design a circuit that has a fixed frequency and duty cycle that happen to be within the required range.

In either case, start with a Schmidt trigger comparator (which is what your circuit above basically is).

The consider how you would turn that into an oscillator without regard to frequency (which means it will be at as high a frequency as the device can produce).

Then consider how you can slow down the frequency by making the rate at which the input voltage changes after a change in output voltage (which your circuit basically does).

Then consider how you can make it so that the change in one direction is different than the change in the other direction (which your circuit basically does).

At each step, work out the mathematical relationships involved and verify that they reasonable match the behavior of the actual circuit.
 

Jerry-Hat-Trick

Joined Aug 31, 2022
592
You can make an astable multivibrator with two transistors and passive components. The component values can be changed to vary the frequency and the mark/space ratio. Easier to use variable resistors called potentiometers to change frequency and mark/space ratio (duty cycle) than variable capacitors. Have you tried googling astable multivibrator?
 

Thread Starter

ahmetkara4635

Joined May 5, 2024
12
I take your comments seriously, but this is for a class project anyway so it's not that important. Thank you. I think I solved my problem, at least part of it.
 

Thread Starter

ahmetkara4635

Joined May 5, 2024
12
On the other hand, when I it realized I used Lm308, not Lm301A(it is my circuit IC) and the circuit is not working well. (Actually when I change the opamp the circuit is not working well in LTspice.Can you help me? My opinion is: Create a square wave, intregrated it, it's a triangular wave, I rectify it with opamp as a full wave rectifier. And I compare them.
 

Thread Starter

ahmetkara4635

Joined May 5, 2024
12
On the other hand, when I it realized I used Lm308, not Lm301A(it is my circuit IC) and the circuit is not working well. (Actually when I change the opamp the circuit is not working well in LTspice.Can you help me? My opinion is: Create a square wave, intregrated it, it's a triangular wave, I rectify it with opamp as a full wave rectifier. And I compare them.
You can make an astable multivibrator with two transistors and passive components. The component values can be changed to vary the frequency and the mark/space ratio. Easier to use variable resistors called potentiometers to change frequency and mark/space ratio (duty cycle) than variable capacitors. Have you tried googling astable multivibrator?
I tried this, I am changing Duty, I can't change the frequency.
 

atferrari

Joined Jan 6, 2004
4,800
I read your post. I wrote " integrated devices such as NE555 that will simplify the issue are banned" And the title including IC's are banned. How can I make a 555 without using logic gates. I am new in the forum. And it's my first post. You are right .I wasn't clear enough
Why don't you reread his post many times until you understand that the reply above should not be?
 
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