Modified Sine Wave with Stable Voltage Output by NE555 (Bipolar)

Discussion in 'General Electronics Chat' started by JUAN DELA CRUZ, Jun 16, 2008.

  1. JUAN DELA CRUZ

    Thread Starter Active Member

    May 27, 2008
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    Hi everyone...:)

    I'm planning to make a Simple Modified sine wave Inverter w/ stable voltage output again..
    ... but now I will use 555 Timer (bipolar).

    My MS-wave Inv. before(LEFT CKT.).... uses an Cmos type 555 together w/ a decade counter(CD4017) that are tricky to find here in our country.

    That's why i decided to make an Inverter again using bipolar type 555 timer instead of the Cmos one.


    Any help/ opinion/ suggestion about the idea is welcome>>>

    Thanks.
     
    Last edited: Jul 2, 2008
  2. Wendy

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    Mar 24, 2008
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    Are you wanting a sine wave output, or a PWM version of the same?

    I have a circuit that has been bubbling in the back of my mind, but it will be a while before I try it.

    It will be a derivative of this one though...

    [​IMG]

    Actually I've got 2 separate ideas that would mesh nicely for this, one for generating a pseudeo sine wave, and the other (shown above) for a Class D Amplifier, which could be used with some modifcations for invertors and straight audio amplification. I pulled this drawing out of my album, for true audio the frequency would be much higher than 6Khz, probably 44Khz (now where did I get that number from I wonder).
     
    Last edited: Jun 16, 2008
  3. JUAN DELA CRUZ

    Thread Starter Active Member

    May 27, 2008
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    Thanks Bill for sharing your brilliant idea...:)

    I want a nearly sine wave output (attached Below).

    I've thought of an idea by summing-up the waveform...
    (sine wave & alternating square/rectangular wave)
    ... to produce my desired waveform(attached Below).


    I chose this waveform instead of pure sine wave 'coz Power Fets/ BJTs will conduct much longer w/ Pure sine wave, therefore wasting a lot of power from the battery as HEAT. But I think in this kind of waveform Power Fets/ BJTs will conduct much shorter compare w/ pure sine wave 'coz of the shape of the waveform.

    Its amplitude must be varies in corresponds to the battery voltage variation (i.e. approx. 13.8V when charge & nearly 10V when discharge) so that 'Stable Voltage Output' of the Inverter can be achieve. Just like my previous MS-wave inverter (attached above),
    ..... but now I will be using 555 Timer (not the Cmos Type).


    Do you think my idea is achievable ??? ......................(I'll attached my design in a few days)

    Thank you for your time.
     
    Last edited: Jun 17, 2008
  4. Audioguru

    New Member

    Dec 20, 2007
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    Hi Juan,
    Your Modified Sine-wave inverter has a square-wave with pauses in it. So its output voltage goes to almost the positive peak voltage of a sine-wave, then goes to 0V for a pause, then goes almost to the negative peak voltage of a sine-wave, then another 0V pause. The average outoput voltage is the same as the RMS voltage of a sine-wave. The 555 and opamps adjust the duty-cycle to regulate the output voltage.

    Bill's circuit uses PWM to modulate a high frequency switched carrier. The modulation is a 50Hz sine-wave and when the output is filtered then it is a 50Hz sine-wave. The output Mosfets switch fully on and fully off so they don't waste power as heat.

    Your waveform idea seems to be more like a square-wave than a sine-wave. Of course the Mosfets will waste a lot of power as heat and the waveform is not a sine-wave.

    Here is a graph of the voltages for a 120V sine-wave, a square-wave and a modified sine-wave:
     
  5. JUAN DELA CRUZ

    Thread Starter Active Member

    May 27, 2008
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    Thanks Audioguru..

    You mean a Pure Sine Wave can be acquired w/ Bill's ckt. even I'll use it in my simple inverter that uses huge xformer???

    Just like in my recent inverter ckt. right?

    Do you think it is possible to make an M.S-wave just by using 555 & op-amps w/ 555 timer ckt as the last stage 'coz I need an output from the ckt. of approx. '200mA' ?

    Thanks
     
  6. JUAN DELA CRUZ

    Thread Starter Active Member

    May 27, 2008
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    I will be using old & inexpensive BJT first ('coz its available here in my province) ... and secondly FETs for this kind of MS-wave inverter.
     
  7. Audioguru

    New Member

    Dec 20, 2007
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    The inductance of a transformer might block the high frequency PWM from Bill's circuit.
    Inverters in stores use a voltage stepup circuit using a small high frequency transformer to make a few hundred volts power supply for the PWM circuit that drives the load directly.

    A modified sine-wave is usually made with an oscillator and frequency divider (in a CD4047 IC) plus a logic gate like a CD4001 or CD4025.

    The circuit you have with a 555 oscillator, opamps and CD4017 sequencer does the same but varies the pulse width a little to regulate the average output voltage.

    Without a digital divider and logic gate or sequencer then I don't know how you will construct a modified sine-wave.
     
    Last edited: Jun 18, 2008
  8. Wendy

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    Mar 24, 2008
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  9. Audioguru

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    You do not want to smooth Bill's PWM sine-wave with an opamp integrator then amplify it with an audio amplifier. Because the audio amplifier is linear and has voltage and current in its output transistors all the time. That makes a lot of heat!

    Instead you want to feed high voltage PWM pulses into into the load with an LC lowpass filter. Then the losses that create heating are low.
     
  10. Wendy

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    If you use this in an inverter circuit just put a cap in parallel with the transformer input, that should smooth it up nicely, maybe with an extra inductor to block the high frequency components of the signal. Basically a low pass filter feeding the transformer. This would prevent high current surges nicely.

    The simple function generator is still a work in concept, but I'm pretty confident the square/triangle section will perform as laid out...

    [​IMG]

    I can see a chance to eliminate an op amp, as is.

    ********************

    Opps, Bill is a parrot today.
     
    Last edited: Jun 19, 2008
  11. Audioguru

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    Dec 20, 2007
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    Hi Bill,
    The 555 in your circuit can be replaced by the second opamp if you don't mind fairly slow edges on the square-wave. Then the virtual ground can be made with two resistors.
     
  12. Wendy

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    I thought of that, and it is always a design option. I was after a clean square wave, which a 555 does nicely, the triangle would follow. I'd like to come up with a comparitor that switches as cleanly as the 555, but no joy yet.

    I also love the exteme predictability of the 555 Schmitt Trigger.
     
  13. JUAN DELA CRUZ

    Thread Starter Active Member

    May 27, 2008
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    Greetings...

    Its been a long time right.....Sorry for not replying guys. 'Coz there was a typhoon hits our country that knockdown Electrical posts including internet lines this pass week.

    Anyways, I've thought of an idea of making PWM M.S-wave inverter again but this time with this waveform output. (Attached below)

    Do you think by converting a PWM square wave (by 555 timer/CD4047 & OP-Amp) to sine wave & a diode in the output of each Op-amp can produce a half sine wave (must be 50% DUTY Cycle) then connect to a LOgic gates that will produce an M.S.-wave waveform, hence, the output will be just like this??? (Attached below)

    And I think by reducing the space between pulses (attached below) can provide a 'Nearly Sine Wave' output.
    Likewise, with this kind of wave form the Power Mosfet in each side can still be 'cooler' 'coz there is still a pause time (OFF). Unlike the M.S.wave output w/ square wave pulses the power mosfet spend more time conducting (i.e. More 'ON' time) that can produce a lot of heat.

    What do you think?????
     
    Last edited: Jun 26, 2008
  14. Wendy

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    This is true of all transistors, the most efficient state for any transistor is fully on, or fully off. It either has no volts or no current, and so no wattage disappated. What creates heat is the in between states, where it is operating in the analog region. This is why a Class D amp is so efficient, it uses the digital modes of transistor operation. I don't think the gaps will help much here.
     
  15. Audioguru

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    Dec 20, 2007
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    With gaps between the excursions of the sine-wave, then it is no longer a sine-wave. The average output power is less due to the gaps so the peak voltage must be increased which adds more heat to the linear Mosfets.
    The linear Mosfets will have the same amount of heat as the load. The battery current is doubled. A very inefficient waste of power.

    A PWM true sine-wave inverter switches the Mosfets completely on (low voltage drop) and completely off (no current) at a very high frequency. With a low voltage drop then no current then the heating is very low. The width of the pulses determines the average output voltage. A small simple filter at the output smooths (averages) the pulses.
     
  16. JUAN DELA CRUZ

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    May 27, 2008
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    Thanks pals...

    Do you know how can I make a this kind of waveform????
    ..........a Sine wave Osc. then a diode on its output then invert it for the another FET???
    ...I think Bill's Ckt. w/ PWM sine wave then a diode also on its output???
     
  17. Wendy

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    Mar 24, 2008
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    Just be aware my circuit is in progress, still has bugs to be worked out.
     
  18. Audioguru

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    Dec 20, 2007
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    What is a diode for?
    First you must determine if your low frequency transformer will pass high frequency PWM.
     
  19. JUAN DELA CRUZ

    Thread Starter Active Member

    May 27, 2008
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    Thanks BIll...
    Can you give an advice on how can I make a PWM sine wave from a square wave more effectively???

    Thanks Audioguru...
    ...to rectify the sine wave just like the half-wave rectifier does. The f of the main Osc. (in my idea) must be 100 Hz or more( PWM half-wave pulses), then divide it for 60Hz, then invert it for the another FET to obtain my desired waveform.

    I won't use high f that requires more complicated ckt. instead I will be using huge Xformer from old microwave oven just like in my previous M.S.-wave inverter.
    I'm just trying to change the output waveform of the Simple PWM inverter.

    I'll post my diagram in a few days.
     
  20. Audioguru

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    Dec 20, 2007
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    Juan, the Mosfets must switch on completely then switch off completely. Your idea uses the Mosfets as a linear amplifier (variable power resistors) that wastes too much power by making heat.

    Mosfets in a linear power amplifier do not work as well as power transistors and need a very high supply voltage that you do not have.
     
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