555 Help

Discussion in 'General Electronics Chat' started by waveguy, Apr 21, 2013.

  1. waveguy

    Thread Starter Member

    Apr 17, 2013
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    Hey guys I hve a 555 circuit producing a signal outputting it into a minature audio transformer... I keep getting flashes of the signal behind the axctual trace signal on the scope... I want to make this signal and circuit as robust as possible without loosing the signal... I actually need this signal turned into an AC signal capapble of handling up to 20 amps....I would sooo much appreciate any help making this circuit the robust heavy duty circuit it truely wants to be :)Ive attatched the circuit and a scope shot.. will someone please help me?
     
  2. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Probably a dumb question, but how are you expecting to get an AC "signal" from a DC square wave?
    What are you trying to make? A more complete explanation will get you more help.
     
  3. Wendy

    Moderator

    Mar 24, 2008
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    You never showed your power supply voltage. There is very little reason you can not drive a MOSFET directly with a +12V power supply. With less voltage you will need a logic level MOSFET.

    An example circuit...

    [​IMG]
     
  4. waveguy

    Thread Starter Member

    Apr 17, 2013
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    Thank you guys for the resonces..

    I have a big problem now... my 555 gets burnning hot soon as i take source of any transistor or FET to ground :/

    Im actually getting an AC wave out of the audio transformer but when connecting it to the gate of the FET the pictured waveform is what comes out :) The thing is ... the pictured waveform is exactly the waveform Im needing but now I need that into an AC waveform... hoping that pushing it thru a bigger transformer will give me the results Im after.

    The power supply Im using is a 12v 1300 miliamp universal power supply but im loosing 10 volts out of the signal when attatching the gate of the FET to it :/ or was... now source to ground is burnning my 555.
    Thank you for that circuit example... the diode CR1 is something i dont have on mine... Im needing to drive a coil of wire to create a magnetic field with this circuit and waveform is more to the point in what I am wanting to do with around or up 20 amps of current thru the coil of wire.Im wanting a variable frequency and duty cycle with the circuit as well but even a fixed frequency of around 1286k will work.
    For the high current section I have a kepco 48-21 power supply .Its a variable voltage 33 -60 volts at 20 amps.
     
  5. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    There are lots of members here that know more about 555 circuits than I do, but this one baffles me. In the first place, I can't tell what all the pins are on your schematic. There are only 7 pins shown, and two of those, I can only guess what they are.

    In the second place, I have no idea what you are trying to accomplish. Your explanations are a complete mystery to me. I can't imagine what you are using an impedence matching transformer for.

    I am interested in 555 circuits and have built more than a few. If I could understand what you are after, I would try to help.

    My guess is that I am not the only member here who is completely in the dark. That may explain why you are not getting many helpful responses.
     
  6. waveguy

    Thread Starter Member

    Apr 17, 2013
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    1
    I see some mistakes ive made drawing it out... i drew pin 1 twice trying to show i have a 470uf electrolytic cap across the + and - .. i failed to draw pin 4 to + and after closer inspection of my soldering job i dont even have pin 4 to anything on my board ... I also forgot to write number 8 on the + connection.I must have willed the waveform into sight because my circuit is just not behaving the last few days.My 555's are cutting out and burnning up now.I need help with a 555 variable negative slope.
     
  7. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    OK, I suppose you don't want to say what you are trying to accomplish.

    Let's forget about AC and "variable negative slope," whatever that is, and just get the 555 working. Apparently, you want an astable multivibrator, and you want to be able to adjust the timing of the pulses. What is the duty cycle range you want, and what is the timing range?
     
  8. waveguy

    Thread Starter Member

    Apr 17, 2013
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    1
    hey Tracecom, my end goal is to create a magnetic field thru a coil of wire with the waveform pictured... im hoping for a duty cylce as close to 90% as i can get starting from 2%.Im also hoping for a frequency range to 10k or beyond starting at 1k.The most important thing is getting the waveform pictured.Ive done this with the circuit posted so i know it can be done.As far as the negative slope.. some ppl call it a true saw tooth while others call it a negative ramp or slope circuit.My problems are the mistakes ive made in building it a proper circuit.I appreciate your help !!!!
     
  9. waveguy

    Thread Starter Member

    Apr 17, 2013
    46
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    Thank you Bill for the example circuit! Im using a 12v 1300miliamp power supply ...I was worried not having enuff current on the the gate.For some reason my circuit isnt working now,the 555 is getting hot when connecting any transistor or FET source to ground.The only FET I had that prodcued the pictured waveform is a IRFPS3810.I dont know or understand why after trying other transistors and FET's the waveform wasnt like the one pictured.The only cap that worked was the 105 code cap on the transformer.
     
  10. waveguy

    Thread Starter Member

    Apr 17, 2013
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    am I in the wrong forum or what?
     
  11. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    As I previously posted, I don't think anyone here understands what you are saying. Post a schematic of what you have built along with photos of your construction, and what it is doing wrong, and someone will try to help. Your verbal descriptions are not understandable.
     
  12. waveguy

    Thread Starter Member

    Apr 17, 2013
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    ok thank you tracecom ill try....

    My camera battery died before i could get a picture of my work station but what i have on a radio shack circuit board is just the 555 part... the transformer and HEXFET are on a breadboard.Im using the transformer to help shape the waveform Im needing.The 555 part is working now,I think I had some wires on the bread board shorting out.My problem now is when hooking up the FET, it kills the signal from the 555 so i get no pulse to the gate of teh FET when I attatch the source pin of the FET to ground.I have tried several resistors from the output of the 555 to gate of the FET and still no luck.I dont know if I need to add any other parts to the 555 to ensure its survival if that makes sence.I dont know if i need to add more parts to the FET to ensure it dont get killed...I allready killed one FET by touching to the source to + i think is what killed it... Im not sure.I need help getting a signal out of the FET now.
    I hope Ive explained my problems good enough but if not i will try again.
     
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  13. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    You do know that a mosfets are used as switches don't you? You do know that a transformer doesn't change the "shape" of a wave?

    In your schematic;
    R3 is doing nothing, the diode makes it ineffective.
    C4 is stopping voltage from going through the primary of your transformer. A capacitor (C4) STOPS the flow of DC. This makes it so your mosfet will never turn on.

    Like tracecom said, tell use what you want to do and maybe we can help. But you have to participate in this too.
     
  14. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    It would be simpler for analysis purposes if you posted the values of C1, C3, and C4 instead of the code. If the code numbers are not underlined, then the corresponding values are C1 = .001μF, C3 = .0047μF, and C4 = 1 μF. Is that correct, or are the codes underlined? Until I understand the answer to that, I can't say whether or not the 555 will perform as an astable multi-vibrator.

    Apparently, what you are after is a pulsed DC power source that is transformed up in voltage by the transformer. Generally, such circuits are arranged with the switching device between the 555 output and input to the transformer. As you have drawn your circuit, if it worked, it would be putting high voltage on the gate of the MOSFET, which would likely destroy the MOSFET. In addition, the transformer you are using is limited to about 1.2 watts.

    As to how to ensure that the waveform looks like the scope trace you posted, I have no idea.

    Where did you get the circuit and what makes you think it will work? And what are you planning to do with the "magnetic field" that you are trying to create?
     
  15. waveguy

    Thread Starter Member

    Apr 17, 2013
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    without R3 and C4 the curcuit does not work as intended at ALL and without the transformer the circuit's waveshaping ability is severely hampered ! R3 controls the circuits slope variability and C4 helps control the circuits waveform...without a 1uf the desired waveform is unabtainable.
    And yes I am aware of what FET's are used for .
     
  16. waveguy

    Thread Starter Member

    Apr 17, 2013
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    Thank you tracecom, I was not aware of the underline on C4, the other caps are not underlined and are the values you stated.
    The only reason Im using that transormer is to obtain the desired waveform Im after.I will be needeing to amplify the signal once we get the circuit to that stage...for now I just need the circuit more less "proofed" and edited if need be so it doesnt get destroyed going into another stage.
    The magneticfield will be used in a metal etching expieriment with oher projects requiring up to 20 amps of current.
     
  17. tracecom

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    I don't understand the output side of the circuit, and really don't think it will work, so I can't be of any help. Maybe there are others here who can understand it. Sorry I wasted your time.
     
  18. vedrit

    New Member

    Apr 27, 2013
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    I'm a little rusty on diodes, but from what I recall, shortbus is right. Test R3 and see how much voltage is flowing across it. My guess is none.
    At the same rate, I don't understand how C4 is keeping the circuit working
     
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  19. waveguy

    Thread Starter Member

    Apr 17, 2013
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    Im getting 8v across R3.. here is the original schematic as i found it on the net somewhere

    C4 doesnt actually kill the circuit if removed... changing values of C4 changes waveshape characteristics.
     
  20. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    Now, there's a circuit which works. It's a sawtooth ramp generator, which is a basic astable multivibrator with a large cap across the output of the 555. The output of the 555 will both sink and source current, so C3 is continually charged and discharged, which changes the shape or the output from a square wave to a sawtooth wave. The two diodes are never used together, but used one at a time; I think D1 will decrease the rise time and D2 will decrease the fall time.
     
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