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    How to get a modified sqare wave with 555 timer?

    hi everyone
    i am building a simple DC-AC inverter for my school project, i am stucked at how to use a 555 timer to generate control signals to control two MOSFET, which will output ON/OFF/OFF to one MOSFET and OFF/OFF/ON to the other MOSFET, is there a simple logic circuit to do the job? ideas?
    thanks

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    Re: How to get a modified sqare wave with 555 timer?

    Quote Originally Posted by ful24 View Post
    hi everyone
    i am building a simple DC-AC inverter for my school project, i am stucked at how to use a 555 timer to generate control signals to control two MOSFET, which will output ON/OFF/OFF to one MOSFET and OFF/OFF/ON to the other MOSFET, is there a simple logic circuit to do the job? ideas?
    thanks
    Generate A Square Wave 1/3 Duty Cycle 1 - 0 - 0

    and it's 180 phase shifted version(not gate ) is 0 -1 -1 ..

    Astable Multivibrator could be used .
    "In the middle of difficulty lies opportunity." -Albert Einstein



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    Re: How to get a modified sqare wave with 555 timer?



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    •   Alt9th August 2011, 06:39

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    Re: How to get a modified sqare wave with 555 timer?

    thanks mister_rf, thats exactly what im after.



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    Re: How to get a modified sqare wave with 555 timer?

    quick question, isnt the discharge supposed to connect between the resistor? ( left side fo the diagram). to make the 555 astable.
    thanks



    •   Alt28th August 2011, 21:52

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    Re: How to get a modified sqare wave with 555 timer?

    Yes, usually it’s better to use a resistor in between the capacitor and the discharge pin, in order to limit the maximum current flow through the internal transistor, but here as the 555 circuit need to fire only short pulses using smaller capacitor values you can skip this resistor. :-D


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    •   Alt28th August 2011, 23:31

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    Re: How to get a modified sqare wave with 555 timer?

    aah, thats why! thanks for the quick reply.



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    Re: How to get a modified sqare wave with 555 timer?

    there is a problem when i breadboard this circuit. there is a delay between the output of the comparator and the flipflop, which results the output of the ANDs are NOT what it suppose to be. is there any way to combat this problem?



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    Re: How to get a modified sqare wave with 555 timer?

    Can you give more details on the timing diagram? :-)




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    Re: How to get a modified sqare wave with 555 timer?

    yes, i didnt save the waveform from the scope, ill do it tomorrow, and it is the Vcomp and Q&notQ out of phase, result the first & second transistor have different waveform form the graph above. ill try to describ it here and ill get the scope waveform later. the actual waveform i got is:
    time 0 30 60 90 120 150 180 210 240 270 300 330 360
    1st transistor on on off off on on off off off off off off off
    2ns transistor off off off off off off off on on off off on on

    ill get it in graph soon.



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    Re: How to get a modified sqare wave with 555 timer?

    Can you attach also the diagram with components types/value used for?



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    Re: How to get a modified sqare wave with 555 timer?

    Click image for larger version. 

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    the first graph is the output of transistor 1 and 2.
    the second graph is the inputs of the AND gate.



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    Re: How to get a modified sqare wave with 555 timer?

    What about some graph for the ‘555’ output and Comparator output?
    What components are you using for? Any details?



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    Re: How to get a modified sqare wave with 555 timer?

    ill upload the details asap. sorry about the inconvenience.



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    Re: How to get a modified sqare wave with 555 timer?

    ok, i used 555timer; 4027(dual J-K flip-flop); LM339(Quad voltage comparator); 4081(Quad 2-input AND gate). circuit is same as the circuit above, resistors and capacitors are used to get a 50Hz and 50% duty cycle. and i didnt terminate any unused pins. i asked the tutor he said its the delay of the 555timer and flip-flop. that caused the phase shift between flip-flop output and comparator output.



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    Re: How to get a modified sqare wave with 555 timer?

    i asked the tutor he said its the delay of the 555timer and flip-flop. that caused the phase shift between flip-flop output and comparator output.
    Doesn't sound reasonable. 4027 and 555 have delays in < 1us range, even the comparator response time is much faster than the delays viewn in your waveform. The circuit must be different from the above suggestion somehow. I would expect a small delay of the comparator output, it may be necessary to apply a correction (e.g. 555 discharge resistor) to avoid a very short pulse at the ramp start.



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    Re: How to get a modified sqare wave with 555 timer?

    It’s very important to have all graphs placed on a new diagram before start to compare timings.



    •   Alt5th September 2011, 16:50

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    Re: How to get a modified sqare wave with 555 timer?

    thanks for the reply gusy, sorry about not posting enough information, i have been very busy attending lectures and breadboarding in the lab, havnt got much time to get on a computer. im going to re-connect the circuit and try different component values. i agree with FvM, ill try to post the circuit diagram asap. (can only view the diagram at school)



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    Re: How to get a modified sqare wave with 555 timer?

    problem solved, the delay i had before was caused by the resistor i placed between "discharge" and "threshold". i re-do the whole circuit again without that resistor, and there is no deplay at all, or acceptable delay.
    anyway, thanks all for the information.



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