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What characterizes a powerFET for audio use?

Discussion in 'Electronic Repair' started by N_Cook, Jan 1, 2014.

  1. Phil Allison

    Phil Allison Guest

    "Maynard A. Philbrook Jr."
    ** Too complicated.

    Q. When you ( full wave) rectify a square wave what do you get?

    A. DC.

    With DC, the average, peak and RMS value are the same.

    Is any proof really needed ?




    ...... Phil
     
  2. Phil Allison

    Phil Allison Guest

    "Maynard A. Philbrook Jr."

    ** Yawnnnnnnnnn - wot a stupid straw man fallacy.

    Read what I dam well wrote - fuckwit.



    .... Phil
     
  3. And where was I disputing that?

    Jamie
     
  4. Phil Allison

    Phil Allison Guest

    "Shaun"
    ** No fooling...........
    ** That sort of nonsense *would* be said by someone who either owned an RMS
    meter or was selling them.

    Thermal RMS meters are virtually obsolete these days and have been replaced
    by cheap analogue RMS to DC computation ICs in many hand held DMMs OR by
    digital sampling computation in most DSOs.

    The hand held kind have a limited measurement bandwidth compared to the
    latter.

    Depends what your needs are.

    As Clint Eastwood might have said -

    " Man's gotta know the limitations of his test equipment ".




    ..... Phil
     
  5. Phil Allison

    Phil Allison Guest

    ** That would be for the actual transmitter on VHF or UHF - right ?

    Same idea as using a glass of water and a thermometer test the power RF
    power of a microwave oven.

    Got SFA to do with the topic.



    ..... Phil
     
  6. Phil Allison

    Phil Allison Guest

    "dave the pig ignorant autistic IDIOT "

    ** No it was not.


    ** A maker's max dissipation spec for a semiconductor is not related to the
    application.

    It is only related to the device itself.

    Normally, the figure given is for *ideal* operating conditions - like when
    mounted on an infinite heatsink held at 20C.



    ..... Phil
     
  7. Leif Neland

    Leif Neland Guest

    Phil Allison skrev:
    Just don't leave the thermometer in the microwave oven with the power
    on.

    Measure the temperature of the cold water, then measure the time for it
    to boil.

    Preferably in a microwave-safe plastic container.

    I measured the power of my previous oven to 230W...

    Leif
     
  8. mike

    mike Guest

    When I did similar tests, I found the order of magnitude was right,
    but the result depended on the shape and volume of the mass of water
    and position in the oven.

    It's easy to imagine that the microwaves bounce around and most of the
    energy ends up
    in the water. Wonder how accurate that model?
    Wonder what the "official" water configuration is when they determine
    the spec?
     
  9. Shaun

    Shaun Guest

    "mike" wrote in message
    When I did similar tests, I found the order of magnitude was right,
    but the result depended on the shape and volume of the mass of water
    and position in the oven.

    It's easy to imagine that the microwaves bounce around and most of the
    energy ends up
    in the water. Wonder how accurate that model?
    Wonder what the "official" water configuration is when they determine
    the spec?

    I've seen that method used before. I had an article about measuring
    microwave oven power. You of course measure the increase in temperature
    after running then microwave oven for a predetermine time at full power,
    with a measured amount of water (distilled) in the direct center of the
    oven. You could google it.

    Shaun
     
  10. Phil Allison

    Phil Allison Guest

    "Leif Neland"
    ** Should be OK with a glass tube and red liquid type.

    ** Bad idea.

    Takes far too long, when boiling first begins is not clear and lots of heat
    is lost to the air and evaporation.

    ** Using half a litre in a plastic jug for two minutes, I got the answer to
    within 10% with a 700W rated oven.

    Having a K-type bead thermocouple and digital temp meter made the job easier
    too.



    ..... Phil
     
  11. Shaun

    Shaun Guest

    "Phil Allison" wrote in message

    "Leif Neland"
    ** Bad idea.
    is lost to the air and evaporation.

    within 10% with a 700W rated oven.
    too.

    You don't run it till boiling! once you get close to boiling point a lot of
    extra energy is required to raise it further and make it boil. What you do
    is run a glass of cold distilled water measured (temp and volume) in a
    container, you could use several stacked Styrofoam cups for insulation and
    cover the top with Styrofoam so that the heat generated does not escape and
    run the oven till the temperature increase 20 to 50 degrees or so, then
    measure the temp, the information will have an equation to convert degrees
    rise to microwave power. Google the method - I haven't looked it up lately.

    Shaun



    ..... Phil
     
  12. Shaun

    Shaun Guest

    "Shaun" wrote in message


    "Phil Allison" wrote in message

    "Leif Neland"
    ** Bad idea.
    is lost to the air and evaporation.

    within 10% with a 700W rated oven.
    too.

    You don't run it till boiling! once you get close to boiling point a lot of
    extra energy is required to raise it further and make it boil. What you do
    is run a glass of cold distilled water measured (temp and volume) in a
    container, you could use several stacked Styrofoam cups for insulation and
    cover the top with Styrofoam so that the heat generated does not escape and
    run the oven till the temperature increase 20 to 50 degrees or so, then
    measure the temp, the information will have an equation to convert degrees
    rise to microwave power. Google the method - I haven't looked it up lately.

    Shaun



    Here is the Method from RepairFAQ from Sam:



    7.1) Testing the oven - the water heating test


    The precise number of degrees a known quantity of water increases in
    temperature for a known time and power level is a very accurate test of
    the actual useful microwave power. A couple of minutes with a cup of
    water and a thermometer will conclusively determine if your microwave
    oven is weak or you are just less patient (or the manufacturer of your
    frozen dinners has increased their weight - sure, fat chance of that!)

    You can skip the heavy math below and jump right to the final result
    if you like. However, for those who are interested:

    * 1 Calorie (C) will raise the temperature of 1 gram (g) of liquid water
    exactly 1 degree Centigrade (DegC) or 9/5 degree Fahrenheit (DegF).

    * 1 Calorie is equal to 4.184 Joules (J) or 1 J = .239 C.

    * 1 Watt (W) of power is 1 J/s or 1 KW is 1000 J/s.

    * 1 cup is 8 ounces (oz) which is 8 x 28.35 g/oz = 226.8 g.

    * 1 minute equals 60 s (but you know this!).

    Therefore, in one minute, a 1 KW microwave oven will raise the temperature
    of 1 cup of water by:

    T(rise) = (60 s * 1000 J/s * .239C/J * (g * DegC)/C)/(226.8 g) = 63
    DegC.

    Or, if your prefer Fahrenheit: 114 DegF.

    To account for estimated losses due to conduction, convection, and imperfect
    power transfer, I suggest using temperature rises of 60 DegC and 109 DegF.

    Therefore, a very simple test is to place a measured cup of water in the
    microwave from the tap and measure its temperature before and after heating
    for exactly 1 minute on HIGH. Scale the expected temperature rise by the
    ratio of the microwave (not AC line) power of your oven compared to a 1 KW
    unit.

    Or, from a Litton microwave handbook:

    Heat one Liter (L) of water on HIGH for 1 minute.

    Oven power = temperature rise in DegC multiplied by 70.

    Use a plastic container rather than a glass one to minimize the needed
    energy loss to raise its temperature by conduction from the hot water.
    There will be some losses due to convection but this should not be that
    significant for these short tests.

    (Note: if the water is boiling when it comes out - at 100 DegC or 212 DegF,
    then the test is invalid - use colder water or a shorter time.)

    The intermediate power levels can be tested as well. The heating effect of
    a microwave oven is nearly linear. Thus, a cup of water should take nearly
    roughly twice as long to heat a specific number of degrees on 50% power or
    3.3 times as long on 30% power as on full power. However, for low power
    tests, increasing the time to 2 minutes with 2 cups of water will result
    in more accurate measurements due to the long period pulse width power
    control use by microwave ovens which may have a cycle of up to 30 seconds.

    Any significant discrepancy between your measurements and the specified
    microwave power levels - say more than 10 % on HIGH - may indicate a
    problem.
    (Due to conduction and convection losses as well as the time required to
    heat the filament of the magnetron for each on-cycle, the accuracies of
    the intermediate power level measurements may be slightly lower).

    Shaun
     
  13. Jeff Urban

    Jeff Urban Guest

    I wanted to reply to this when you first posted it but I couldn't for
    whatever reason. fucking thing. As you can see I am not posting from
    google, which I no longer capitalize !!!! LOL

    Anyway, what characterizes ANY part for the transmission of audio is
    linearity. Even though the gate of a MOSFET is driven wildly different
    than the base of a BPT, linearity of gain fro the very small signal to
    the very large signal is the prime. We used to look at the hfe and HFE
    gain curves of bipolars in the old days, not it is different.

    Any kinds of spurious shit like oscillations would be no good in
    switcxhers as well. the thing is, switchers somethimes have a gain curve
    that is like, made to be on or off.

    An audio transistor must operate in the analog range, that means the
    gain curve should be as flat as possible through the operating current
    range.

    The same is true of a MOSFET.
     
  14. N_Cook

    N_Cook Guest

    Ah at last , thanks, a pertinent reply to my original question. I was
    wondering if it was a larger area of silicon so the heat can migrate out
    of the die quicker. So from what you say a non-audio switcher mosfet
    could be used for analogue but the power rating would have to be derated
    and no other qualification for such use, anymore than usual precautions
    you would use for a switcher situation. I suppose the amount of derating
    would then depend on the type of use bass amp v GP audio amp, dance
    music v classical music etc
     
  15. Phil Allison

    Phil Allison Guest

    "Nutcase Kook is yet another pig ignorant pommy ****"


    ** The Semelab app note makes it pretty clear there is a HUGE difference
    between "switching" and audio ( ie lateral) power mosfets.

    http://products.semelab-tt.com/pdf/ApplicationNoteAlfet.pdf

    ** Yawnnnnnnnnnnnnnnn....

    More brainless, fucking TROLLING !!!!!!!

    FOAD you vile pommy cunthead.



    ..... Phil


    ** There is no possible answer to a question as wrong headed and stupid as
    that.

    So you will never get one.

    FOAD you vile pommy cunthead.




    ..... Phil
     
  16. N_Cook

    N_Cook Guest

    or on rereading . If an audio application can tolerate a certain amount
    of cross-over distortion and general harmonic distortion then there is
    no difference in powerfet useage type , up to some power level where
    these distortions become too apparent.
     
  17. Guest

    I don't know about a US Federal Trade Commission (or other agency, or
    equivalent in other countries) test procedure; there probably is one but
    I don't know it.

    I know that older GE microwave ovens, in the little service information
    sheet that was folded up inside the oven, gave directions on the test, a
    GE part number for a beaker you were supposed to use, and I think a
    third-party part number for the thermometer you were supposed to use to
    measure the water temperature before and after. I think the water level
    was marked on the beaker, and the service sheet said to put it right in
    the middle of the oven. You didn't boil it, just heated it for a fixed
    amount of time.

    If I remember right, the criteria was something like "if the oven
    produced between X and Y degrees temperature rise in the water, it's
    within spec" - it didn't give you an answer in watts, just an acceptable
    temperature range for that particular model oven.

    Matt Roberds
     
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