I need help about DC-AC Inverter

Discussion in 'General Electronics Chat' started by waldopulanco, Nov 16, 2013.

  1. waldopulanco

    Thread Starter New Member

    Nov 14, 2013
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    2 years ago i have created a 150 watts DC-AC Inverter (12 VDC input and 220VAC Output) i was found the Schematic Diagram here http://www.sm0vpo.com/power/invert1_00.htm

    then after i built, i test it and it was fine with the 80 watts bulb i try to bulb 100 watts but the light was dim!! then i try it to Flourecent with starter but the output voltage was drop to 50vac during the start, and i try it to colored tv 80 watts but after the click the power button the output voltage from in verter was drop to 50vac!!

    then i try it to simulate using Tina Design Suite and there is a problem to when i load a bulb of 100watts the output voltage was drop to 150vac!! but when i try to 50 watts bulb it was fine!!

    here is the simulated diagram using Tina Design Suite!!
    [​IMG]

    help me to make it perfect!! because my inverter was never to use because of this problem!!

    thanks!!!
     
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    What voltage do you use as input voltage?
    If you are using 12 Volts, the regulator will not work properly and give about 9 Volts at its output.
    Also reduce the values of R7 and R8 to about 100 Ohms to drive the fets better.

    Bertus
     
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  3. waldopulanco

    Thread Starter New Member

    Nov 14, 2013
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    im using 12volt battery 12volt 48 ampere!! ok i will try to reduce the R7 and R8!!
     
  4. wayneh

    Expert

    Sep 9, 2010
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    I think Bertus has nailed it. I haven't studied the schematic but I suspect you could eliminate the regulator altogether and get better results.
     
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  5. t06afre

    AAC Fanatic!

    May 11, 2009
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    But is not the regulator for the control circuitry only. And the FETs are feed directly from the 12 volt source. I read the schematic that way. But I am no expert on inverters
     
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  6. Brownout

    Well-Known Member

    Jan 10, 2012
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    You can't run the multivibrator on 12V. The voltage must be kept at 9V or below.
     
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  7. wayneh

    Expert

    Sep 9, 2010
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    Yes, but the control circuit ends up on the gates of the MOSFETs. If they are not switched hard, no joy.

    Oops, brownout beat me.
     
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  8. bertus

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    Hello,

    When the multivibrator must run below 9 Volts, use an 7808 regulator and logic gate mosfets.

    Bertus
     
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  9. t06afre

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    Ah...so the problem may be that FETs is not turned on hard. I did not think of that.
     
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  10. Alec_t

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    Why? Personally I'd just ditch the regulator and replace it with a diode, so that high current through the FETs doesn't cause the multivibrator supply to sag significantly. If you're worried about the 12V causing breakdown of the base-emitter junctions when the bases are driven negative then a diode in each emitter (or base) path would prevent that.
     
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  11. bertus

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  12. t06afre

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    Can you elaborate on why the multivibrator not can be run on 12 volt. As I remember the LM358 may work up to about 30 volt as supply voltage. But this is a circuit type (inverterters) I know very little about
     
  13. Brownout

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    Jan 10, 2012
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    What's the maximum reverse B-E voltage? Typically, 12V will exceed this spec.

    Look at the 3rd and 4th graph under fig. 12 on the link posted in post #11 above. It shows that the peak reverse B-E voltage is -VCC.
     
    Last edited: Nov 16, 2013
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  14. waldopulanco

    Thread Starter New Member

    Nov 14, 2013
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    i remove the LM7812C Regulator then i place a diode and it was improve slightly than LM7812C!!
     
  15. waldopulanco

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    Nov 14, 2013
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    i see The schematic is in figure 14. and i think it is better than one!! its cascading and i think it is stable!! i try it to feed in LM358 and see the result!! but how to know the Square wave frequency? i need 60 hz!!
     
  16. ronv

    AAC Fanatic!

    Nov 12, 2008
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    The oscillator is a problem, but it is not the problem you started the thread for. The 12 volt regulator also doesn't regulate much since it is on a 12 volt battery. But that's probably not it either.
    The low power problem might be your choice of FETs (high Rds on), the battery voltage under load or maybe the transformer. (is it big enough)
     
  17. waldopulanco

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    Nov 14, 2013
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  18. waldopulanco

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    Nov 14, 2013
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    i replce the 12volt regulator with diode!! and its better than 12v regulator!!

    here is the screenshoot:
    [​IMG]


    But i need to improve it!! i think the wave form is not a perfect!! hope you can help me!!

    thanks a lot!!
     
  19. Alec_t

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    Sep 17, 2013
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    Try the circuit shown in Fig 15 of that link to improve the waveform, but also include a diode in each emitter (or base) path to prevent reverse breakdown of the base-emitter junctions.
    In your schematic above, try R5 = 22k instead of 2k2 so that the LM358 switches at around half the supply volts.
     
    Last edited: Nov 17, 2013
  20. Brownout

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    Jan 10, 2012
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    You can't replace a regulator with a diode. It won't work in a real circuit. The regulator was there for a reason (given in the thread context)
     
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