40% duty cycle square wave generator circuit.I need help to develop this circuit

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navinthan

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hi there,im a student.im assigned by my groupmates to create this circuit.i js cant find any information about it.hope any of the members can help me.the frequency adjustable will be between 1-10KHz.thank you.
 
I guess they assigned you this task because none of them have a clue how to do it. I'll give you help in two steps.

Tell me, what is the step response of a series RC circuit when there is no voltage on the capacitor.

Tell me, in a series RC circuit with the voltage on the capacitor equal to the supply voltage what is the step resonse when the switch to the supply is opened.

Express the results V(t) = ... where V(t) is a function of time, t and Vo, R, and C are parameters.

Some other spoilsport will probably just give you the answer in which case you will have learned nothing.
 
Search Google for 555 timer tutorial. I've seen atleast three sites containing such information, there is also an online wizard some place.
 
HarveyH42 said:
Search Google for 555 timer tutorial. I've seen atleast three sites containing such information, there is also an online wizard some place.
Click to expand...
Ya spoilsport! I knew that someone could not resist giving the game away.
 
I don't think I spoiled it just yet. There is still much for him to do, in order to answer the question or design the circuit. Just point him to the resources he will need, whether he makes use of them is another story. If doesn't come back with some sort of circuit, guessing this is just another 'do it for me' request...
 
Can a 555 timer gives 40% of duty cycle? I thought the minimum is not less than 50% with the formula (R1+R2)/(R1+2R2) ??
 
bananasiong said:
Can a 555 timer gives 40% of duty cycle? I thought the minimum is not less than 50% with the formula (R1+R2)/(R1+2R2) ??
Click to expand...

What's the difference between 40% and 60%?, merely one of polarity - in any case, it's simple to make the mark/space adjustable over a wider range.
 
Huh! I didn't know that! What I've learned is up to 50% of duty cycle only. How to make it? Is it set to 60% and then put an inverter at the output?
 
bananasiong said:
Huh! I didn't know that! What I've learned is up to 50% of duty cycle only. How to make it? Is it set to 60% and then put an inverter at the output?
Click to expand...

Yes, it's hardly complicated is it?.

But, like I said, it's EASY to make the mark/space fully variable - I'll give you a hint - 'two diodes'.
 
You can bypass one of the resistors with a diode to get <50% duty cycle (see datasheet).

Anyway having a variable frequency from 1kHz to 10kHz with a fixed duty cycle of 40% isn't as easy as just bulding a simple 555 timer oscillator.

I think a schmitt trigger oscillator will do the job, failing that a variable 50% duty cycle 555 oscillator with a comparator on the timing capacitor will work for sure.
 
Yes I found it, thanks. I didn't notice that. The other diode is optional right? So the frequency calculation will be different?
 
still on the circuit

i manage to figure out how the circuit will look alike.but still working on the values of the components.the other information given to me is:
>The output should have an adjustable linear output voltage range of between 0 to 5 V and be capable of supplying a current of 150 mA throughout the voltage range.
 
There are many ways to do this. I would just add a 100ohm potentiometer followed by a complementary push-pull emmitter follower on the output.
 
thanks

thanks for the help.i manage to figure out the circuit.js had troubles in determining hte component values.anyway its done.thank again to every1.
 
i end up using 555 ic timer.i dont have the schematic diagram with me now.i'll post it once get it from my groupmate.thank you.
 
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