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Square Wave Based Inverter (Switch Mode)

Discussion in 'Alternative Energy' started by C47, Apr 21, 2008.

  1. C47

    C47 New Member

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    I am building this circuit (12DC to 12VAC) and I am having problems, first of all for the VPULSE, what should I use, a 555 timer or ua741 opamp to create a square wave....

    the bigger problem is how many independant vpulse should i have....two are still managable but four are very difficult to syncronize

    im pretty much late (for my project) here so dont post any more complicated inverter designs..

    i removed the protection diodes for the time being....
     

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  2. mvs sarma

    mvs sarma Well-Known Member

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    Welcome to the site. C47.
    It would be better to use 555 followed by buffers to get more outputs of the same signal. If you want complimentary outputs , you may use 55 at double the frequency, divide it by2 and use the "Q" and "/Q" outputs. By the division method, you achieve 1:1 pulse ratio.
     
    Last edited: Apr 21, 2008
  3. C47

    C47 New Member

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    thankyou sarma,


    tha complimentary idea is billiant if it is in the chip itself....

    the problem with the 555 timer is also that is starts with 48Hz and climbs upto 52Hz , ie for some reason its not stable

    Im using the NE555P and its doesnt have the Q'...please help
     

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    Last edited: Apr 21, 2008
  4. dave

    Dave New Member

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  5. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    Its not just the Vx drive pulse generator thats the problem.

    V4/5 are in opposite phase as are V2/3. Alternating.!

    V2 and V5 need to be ON at the same time, with V3 and V4 OFF, then on the next cycle,
    V2/5 OFF and V3/4 ON.

    The problem arises using 555 is the level shifting for the V2 and V3 pulses as they are not referenced to 0V.

    Summary:

    Only two phases, but V2 and V3 need level shifting.

    Do you follow.?

    EDIT: I am assuming that you require the 12Vac across the inductor.???

    With ref to the 555 osc frequency drift, please post your circuit, what R,C type components are you using.?
     
    Last edited: Apr 21, 2008
  6. C47

    C47 New Member

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    the problem is of the GND.....please stay and tell me:

    what you mean by level shifting and if i manage to do that what should i do with the GNDS of V2 and V3? where should i put them....at the emitters of the top BJTs?

    also are you suggesting to use one 555 timer? coz thats not possible becoz of gnd connections...
     
  7. C47

    C47 New Member

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    ericgibbs thankyou for helping.....

    as for your reply to the edit:

    well the capacitor and inductor were kind of loads...filters sort of things....please excuse my ignorance....i can run the circuit in PSpice with R as a load only too....but the problem is implementing it in real life
     
  8. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    This what I said.

    See edit to my last post.
     
  9. C47

    C47 New Member

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    the 555 circuit:

    Ra = 1kohm
    Rb = 51K+91K
    C = 0.1uF

    and the 0.01uF is the same as in my circuit

    ericgibbs please suggest how many 555 should i use?

    DUTY Ratio = 49%

    EDIT: I didnt use Pspice for the 555 i just tested it manually and changed RB with a potentiometer when i got 50Hz i put in a fixed resistor
     

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    Last edited: Apr 21, 2008
  10. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi C47,

    The original circuit, must you follow that design using those types of transistors.

    The top two are connected as emitter followers and the bottom two as common emitter. The top two should be pnp transistors.

    Is it permitted to change the original design.?
     
  11. C47

    C47 New Member

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    well as long as it works.....but i dont see how pnp for the top two would help...what about the GNDs then...will they be connected to the pnp collectors?
     
  12. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    I'll post a drawing, shortly.:)
     
  13. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi C47,
    This is a very basic circuit in order to demonstrate the idea.

    As its a 'project' it would best if you calculated the required values.:)

    Do you follow it OK.?
     
    Last edited: Jul 7, 2008
  14. C47

    C47 New Member

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    well what are those empty boxes and where did the 12V go?

    and whats the red transistor for?

    and where are the drives for the top two?

    is this a half bridge rectifier?

    EDIT : is this supposed to get rid of syuncronization issues
     
    Last edited: Apr 21, 2008
  15. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi C47,
    What college year is this project for.?:rolleyes:
     
  16. C47

    C47 New Member

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    well for q3 i will use an opamp inverter, is that okay?

    im sorry i didnt understand the linking resistor part?

    is the red 5V suuposed to be 12V or is it part of the BJT inverter that you meant to use?
     
  17. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    Last edited: Apr 21, 2008
  18. C47

    C47 New Member

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    im simulating it in pspice i will use vpulse instead of 555, so its faster and its 14V (sorry my mistake) so that the bjts can operate in switch mode
     
  19. C47

    C47 New Member

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    i just popped the 555 when i connected to output to base of the red transistor....are you sure of your circuit?
     
  20. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    Yes Im sure.

    What value of resistors do you have in the 555 output to the transistor and opa invertor.?

    EDIT: post a drawing with the component values on.
     
    Last edited: Apr 21, 2008
  21. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    Double checked my circuit, OK

    If you have popped the 555 you have connected something incorrectly.

    Check the supply to the 555 timer make sure its not greater than 15V or so volts, also the connections to the 555, especially pin #3.
     

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