pulse width modulation with ne555

Discussion in 'The Projects Forum' started by Steve555, Oct 11, 2006.

  1. Steve555

    Thread Starter New Member

    Oct 11, 2006
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    I need to know if I can change the pulse width on a ne555. At the moment I have a curcuit the uses a 2k pot on pins 6 & 7 to 12v with a .01uf from pins 6 & 7 to ground. This is not working for me. It does not change the output signal.
    Can anyone tell me what is suppose to happen when I change the voltage on pin 5 of the ne555, cos nothing is happening and I cant see that it will do anything by the time it goes through the transistor (IFR540).

    Thank you for looking into my problem.
    Your help will be apreciated.
     
  2. n9352527

    AAC Fanatic!

    Oct 14, 2005
    1,198
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    You should be able to change the pulse width by varying the voltage on pin 5. On monostable mode, where pin 6 and 7 is tied together like your configuration variation of voltage on pin 5 from around 0.5 to 0.9 Vcc will vary the pulse width. On astable mode variation of voltage on pin 5 from about 1.5 to Vcc will vary the frequency as well.

    This is a poor man's PWM, where the frequency and the duty cycle vary with control voltage. It is fine for some purposes but not on others where the frequencies interfere with other parts of circuit.
     
  3. Steve555

    Thread Starter New Member

    Oct 11, 2006
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    Thank you n9352527
    I'm looking for a better way to do this but this is what I have to play with.
    I have a LM741 controling the volts on pin 5 of the NE555 but it does not go down that far, starts at around 1v.
    I do have a functional genarator where pin 6 & 2 of the TLC555 go to a wave form switch and pin 3 goes to pin 3 on the LM13600. Pin 7 on the TLC555 goes no where pin 5 goes through a 10nf to ground. Could you suggest a way to change this circuit pulse width moduation.
    Thanks for your time on this
    Steve
     
  4. n9352527

    AAC Fanatic!

    Oct 14, 2005
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    Could you elaborate on what you are trying to do? And if possible post your circuit?
     
  5. Steve555

    Thread Starter New Member

    Oct 11, 2006
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    This is the circuit i would like to adjust the pulse width. I can put a mosfet driver and transistor on the out put later.
    View attachment pulse gen.pdf

    This is the circuit I have that is suppose to do pulse width adjust but not working.
    View attachment waterfuela.pdf

    It is an experiment for hydrogen production. This needs to be right before I can buid the main chaimber. The freq needs to adjust for the tuning of the electrodes and the width controls volts or how much current you let it use. I'm trying to get good efficency on about 1 amp.
     
  6. n9352527

    AAC Fanatic!

    Oct 14, 2005
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    I don't see any problem with the water vapour circuit. Do you get any pulse at all at the output? Or was it just the width modulation that doesn't work?

    The pulse generator is a different circuit altogether. I don't think you can drop the modified 555 circuit from the water vapour there and able to adjust the pulse width.
     
  7. Steve555

    Thread Starter New Member

    Oct 11, 2006
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    Thanks I'll keep on trying to get it to work. Its just the puse width not happening.
    Your help has been fantastic.
    Thank you.
     
  8. Steve555

    Thread Starter New Member

    Oct 11, 2006
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    My water vapour circuit can only vary pulse width on the highest pulse switch. Is there another way to do this, a better circuit. I tried to modify a dc motor controller but the ic does not like the the high frequency pulse rate. It was designed for about a 2k pulse rate. This is what happens when it starts to go crazy.
    scope wave1.jpg
     
  9. vigneshwaranj

    New Member

    Oct 10, 2006
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