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LT SPICE transformer

Discussion in 'General Electronics Chat' started by MrDEB, Apr 29, 2010.

  1. MrDEB

    MrDEB Active Member

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    pc board layout using TO-3

    here is my pc board design using the TO-3 package transistors
    Will still install a heat sink as the board is only 1 oz (2 oz if the design fits my 2oz copper boards
     

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  2. MrDEB

    MrDEB Active Member

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    Havn't done any work using Mosfets but I understand they are superior over transistors.
    Would two P channel and two N channel Mosfets work more efficiently than the four transistors in this amp??
     
  3. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Mosfets conduct so well that the speakers will get the entire supply voltage and the mosfets will get barely warm.
     

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  4. dave

    Dave New Member

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  5. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    They aren't 'superior', they have some advantages, and some disadvantages - as shown by the fact that they are still VERY much a minority.
     
  6. MrDEB

    MrDEB Active Member

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    So then the mosfets would be a better choice over the transistors being that the mosfets won't get warm??
    schematic is pretty much the same maybe I will make changes? for a more efficient amp in that the mosfet amp won't generate any heat. HEAT is in a sense wasted energy.
     
  7. Sceadwian

    Sceadwian Banned

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    MrDEB, everything generates some heat. If you can live with a square wave a fast Mosfet will generate very little, if and only if it's driven properly.
     
  8. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Heat, in this case (and most others) is ENTIRELY wasted energy.

    Correctly designed systems, either MOSFET or bipolar, will minimise excess heat - but there's no 'magic' using MOSFET's - and certainly commercially MOSFET's have proven more expensive and less reliable in SMPSU's and LOPT stages, and they don't run any cooler.
     
  9. audioguru

    audioguru Well-Known Member Most Helpful Member

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    This square-wave H-bridge circuit is not a linear amplifier. The Mosfets switch with much more efficiency than bipolar transistors.
     
  10. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Neither are SMPSU's or LOPT stages linear, and neither of those benefit from MOSFET's in any way.
     
  11. MrDEB

    MrDEB Active Member

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    Now boys if you two can't agree then I will have to send you both to your rooms!!



    LOL
    will look at both options. Using the Mosfets may not need a heat sink but thats a monor issue I think?
    Will run the circuit using the 50 ohm resistors instead of the 33 ohm and see how much it gets hot!
    If it is too hot (can't touch) then on to Mosfets.
    And what is a SMPSU or LOPT??
    inquiring mind wants to know
     
  12. Sceadwian

    Sceadwian Banned

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    What do you mean Nigel, both SMPSUs and LOPTS both benefit from using Mosfets over bipolars, why would you say that?
     
  13. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    So why are they hardly ever used?, why d0on't they run cooler (because they don't), and why are they less reliable on the few sets which have used them (because they are less reliable).
     
  14. Sceadwian

    Sceadwian Banned

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    In what devices Nigel? You obviously have specific devices you have in mind when you think of Mosfets in a switching power application which obviously don't speak for all power mosfets in a power switching situation. Mosfets are used extensively in switched mode power supplies for motors and for UPS supplies. You seem to be talking TV sets when that is not the only place where such devices are used. In the case of a piezoelectric driver where distortion isn't even considered in general as any harmonics created can't propagate because of attenuation mosfet drivers can be extremely efficient.
     
    Last edited: May 15, 2010
  15. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Mostly domestic appllications, including TV's - where MOSFET's have become popular though is in LCD and Plasma sets.

    My point is that there seems a small number of people who seem to think MOSFET good, bipolar bad, and this isn't the case. MOSFET's have there uses, but it's not a universal replacement, for many purposes bipolar are far more suitable, and much more reliable.
     
  16. MrDEB

    MrDEB Active Member

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    WHY no criss cross?

    Hope I crossed ref the mosfets correctly but why are the outputs from the P channel not criss crossed like the transistor version?
    And then in your schematic you show 10K base resistors for the 2n2222's
    need to add??
    link to selected mosfets.
    I have NEVER worked with Mosfets
    https://www.mouser.com/Search/ProductDetail.aspx?R=FQP17P10virtualkey51210000virtualkey512-FQP17P10

    https://www.mouser.com/Search/ProductDetail.aspx?R=FQP33N10virtualkey51210000virtualkey512-FQP33N10
    this version should run cooler?
     

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  17. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Those Mosfets might cost more than others because their max voltage is 100V. Mosfets rated at 30V might cost less.
    The 2N2222 or any other little NPN transistor has a load of only 12mA in your circuit so it needs a base current of only 1.2mA. Then the base resistor can be 3.3k ohms.
    The 1.2k resistor can be 10k or 33k.
     
  18. MrDEB

    MrDEB Active Member

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    Something like this?

    And why are the outputs not cris crossed like the transistor version.
    Will look at different Mosfets. I selected ones that were similar to the IRF6215 / IRF540 as in the schematic you posted.
    QUESTION concerning base current of the 2n2222. Is not the load the same on both ( even though the 150 ohm (R11 is there)?
     

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  19. audioguru

    audioguru Well-Known Member Most Helpful Member

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    I just noticed that your P-channel Mosfets are upside-down. The sources must be at the positive supply, not at the speaker.
    The input of a Mosfet draws no current, but a signal must quickly charge its input capacitance for a moment. Therefore the 2N2222 or any other little NPN transistor has no load and its collector resistor can be much higher than 150 ohms and its base current can be much lower.

    R9 and R11 can be 3.3k ohms.
     
  20. MrDEB

    MrDEB Active Member

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    Thanks will make changes
     

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