40% duty cycle square wave generator circuit.I need help to develop this circuit - Electronic Circuits Projects Diagrams Free

navinthan · 15th October 2006, 05:41 PM

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.

Hero999 · 15th October 2006, 06:20 PM

Do your own work.

1 v0te 4 b1n.

Papabravo · 15th October 2006, 06:27 PM

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.

HarveyH42 · 15th October 2006, 06:35 PM

Search Google for 555 timer tutorial. I've seen atleast three sites containing such information, there is also an online wizard some place.

Papabravo · 15th October 2006, 06:37 PM

Quote:

Originally Posted by HarveyH42

Search Google for 555 timer tutorial. I've seen atleast three sites containing such information, there is also an online wizard some place.

Ya spoilsport! I knew that someone could not resist giving the game away.

HarveyH42 · 15th October 2006, 06:55 PM

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...

bananasiong · 15th October 2006, 07:12 PM

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) ??

**Nigel Goodwin** · 15th October 2006, 07:16 PM

Quote:

Originally Posted by bananasiong

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) ??

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.

bananasiong · 15th October 2006, 07:33 PM

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?

**Nigel Goodwin** · 15th October 2006, 08:42 PM

Quote:

Originally Posted by bananasiong

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?

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'.

Hero999 · 15th October 2006, 08:43 PM

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.

bananasiong · 16th October 2006, 02:44 AM

Yes I found it, thanks. I didn't notice that. The other diode is optional right? So the frequency calculation will be different?

penoy_balut · 16th October 2006, 03:08 AM

to vary duty cycle in 555, make a different resistance for charge and another for discharge.

navinthan · 16th October 2006, 02:53 PM

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.

Hero999 · 16th October 2006, 07:20 PM

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.

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15th October 2006, 05:41 PM	#1
navinthan	40% duty cycle square wave generator circuit.I need help to develop this circuit 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.

15th October 2006, 06:20 PM	#2
Hero999	Do your own work. 1 v0te 4 b1n. __________________ I do not answer private messages asking for help because no one else can: benefit from advice I may give or correct me if I'm wrong. Please ask on the open forum if you have a question and I'll be happy to help, if I know the answer.

15th October 2006, 06:27 PM	#3
Papabravo	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.

15th October 2006, 06:35 PM	#4
HarveyH42	Search Google for 555 timer tutorial. I've seen atleast three sites containing such information, there is also an online wizard some place.

15th October 2006, 06:55 PM	#6
HarveyH42	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...

15th October 2006, 07:12 PM	#7
bananasiong	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

15th October 2006, 07:33 PM	#9
bananasiong	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

15th October 2006, 08:43 PM	#11
Hero999	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. __________________ I do not answer private messages asking for help because no one else can: benefit from advice I may give or correct me if I'm wrong. Please ask on the open forum if you have a question and I'll be happy to help, if I know the answer.

16th October 2006, 02:44 AM	#12
bananasiong	Yes I found it, thanks. I didn't notice that. The other diode is optional right? So the frequency calculation will be different? __________________ bananasiong

16th October 2006, 03:08 AM	#13
penoy_balut	to vary duty cycle in 555, make a different resistance for charge and another for discharge.

16th October 2006, 02:53 PM	#14
navinthan	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.

16th October 2006, 07:20 PM	#15
Hero999	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. __________________ I do not answer private messages asking for help because no one else can: benefit from advice I may give or correct me if I'm wrong. Please ask on the open forum if you have a question and I'll be happy to help, if I know the answer.