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Type: Posts; User: c_mitra

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  1. Closed: Re: Extracting energy from gyroscope precession

    I am sorry that I am not understood.

    Motor is a source of energy. A gyroscope must be free (from external forces)- I am talking about mechanical gyroscopes here.

    A spinning object mounted in...
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    Closed: Re: would iron wire block high frequencies

    Yes, but thin wires will have only a small effect. Imagine a straight long iron wire carrying some current. The magnetic lines of force will be circular, perpendicular to the wire and will see only a...
  3. Closed: Re: Is it possible to make an IGBT to work at duty cycles up to 100%?

    Right.

    If you want a 100% duty cycle, why do you need a switch at all? It is not going to be turned off, right?

    But how a chopper is going to work with a 100% duty cycle? MY knowledge is...
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    Closed: Re: Driving 140x 3W LEDs

    I believe the LEDs have already some form of heat sink- there is a central pad on the reverse which is expected to be soldered to a board (in this case the PCB). With 70 LEDs dissipating 3W each...
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    Closed: Re: Driving 140x 3W LEDs

    I do not think the 24R is god-given; you need to calculate the value based on your current requirement. The reference voltage is 1.25V=700mA *R; that makes R=1.8 Ohm; this should be rated at...
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    Closed: Re: Six-Pulse Rectifier Capacitor Value

    I have discovered that graphical description is very helpful if you have questions.

    155425

    A single sine wave after rectification (full wave) becomes twice the frequency. Half wave...
  7. Closed: Re: 3 phase 4 wire(480V) AC to 12VDC (100mA) power supply for energy metering applica

    I do not see how it can be done in a simple way; you will certainly need 3 nos 1W 480V 12V transformers. The outputs can be paralleled via a diode.

    You may find it difficult to get 480V...
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    Closed: Re: Well regulated mains to large cities

    True but the power to your home comes from a local (relatively) transformer that is perhaps a 3-phase to 3-phase one supplying perhaps 10-20 nearby houses.

    Once our local distribution transformer...
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    [SOLVED]Closed: Re: Energy Band Model and Energy bond Model

    Electrons are labelled by their quantum numbers. All electrons in an atom has different quantum numbers. (quantum numbers in a molecule are labelled differently: core and valence electrons).

    But...
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    Closed: Re: PN junction in thermal equilibrium

    The majority carriers are coming from doping. On the p-side, the holes are mobile but the electrons are not; on the n-side the electrons are mobile but the holes are not. Why? The impurity levels are...
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    Closed: Re: PN junction in thermal equilibrium

    Right. AND this tends to lower the junction potential. As the junction potential decreases, diffusion of majority carriers take place- that increases the junction potential.

    This can be seen when...
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    [SOLVED]Closed: Re: Energy Band Model and Energy bond Model

    1. No; energy band model is obtained for a crystal with no defects. Defects are introduced as perturbations. Defects are randomly placed and individual placements are of no consequence.

    2. The...
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    Closed: Re: PN junction in thermal equilibrium

    With ZERO external bias. There is an internal bias due to the junction potential.

    Yes, there is a continuous diffusion current and that is exactly balanced by the current due to the minority...
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    Closed: Re: power consumption and temperature rise

    Of course the temperature is increasing. The question is how much?

    If the resistor is well insulated, the heat produced will have nowhere to go and the temp will rise linearly with time. But no...
  15. [SOLVED]Closed: Re: Inductor quality value for switching regulators

    Right, in a field free space. But I do not know if the single straight wire of circular cross section is parallel to a metal object; or is surrounded not by vacuum (what will be the impedance).
    ...
  16. [SOLVED]Closed: Re: Inductor quality value for switching regulators

    I guessed it but it is wrong to call it "AC resistance" because of several reasons.

    1. You cannot define an AC resistivity because it depends on the geometry of the conductor. A foil or a cylinder...
  17. [SOLVED]Closed: Re: Inductor quality value for switching regulators

    I am learning new things. Do you have some reliable references where I can learn more about the AC resistance of copper?

    Resistance of metal increases with temp- due to phonon electron scattering....
  18. [SOLVED]Closed: Re: Inductor quality value for switching regulators

    True.

    For a comparison, metals like Ag, Cu and Au (the coinage metals) have more than a million times less resistivity (of the order of 1E-8) ...

    These values (resistivity of common ferrites)...
  19. [SOLVED]Closed: Re: Inductor quality value for switching regulators

    Most ferrites have very high electrical resistivity and that means that the eddy losses are very low.

    What you are seeing is called hysteresis loss; it is dependent on the area of the hysteresis...
  20. Closed: Re: Thermal camera reading fet temperatures...how far away to hold it?

    The specifications says:

    "Field Angle / Shortest Focal Length: 27'×35'/0.5m
    Thermal Sensitivity: 0.07'C
    Measuring Mode: Thermopile
    Temperature Range: -20'C to 300'C(-4'F to 572'F)
    Measuring...
  21. [SOLVED]Closed: Re: Inductor quality value for switching regulators

    Of course I have a very very limited knowledge. So I looked up other places:

    1. Wikipedia is reasonably decent reference. It says

    "In physics and engineering the quality factor or Q factor is a...
  22. [SOLVED]Closed: Re: Inductor quality value for switching regulators

    Inductors are basically current device; they do well at high current (unlike capacitors that do well under light load).

    For switching regulators, there will an optimum load at which the efficiency...
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    Closed: Re: Doppler "radar" motion detector design

    A nice thing to play around. Does it go through the wall? RF should be able to pass through the door and walls (but I do not know about the reflected beam)...
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    Closed: Re: Single conductor inside hollow conductor

    If the voltages are small enough, there should be no problem.

    In my student days, I have seen electromagnets made with copper tubes covered with cotton threads and heavily varnished. Water mixed...
  25. [SOLVED]Closed: Re: Inductor quality value for switching regulators

    You are right; Q is meaningful only for a resonant system but for an ideal inductor, Q cannot be defined.

    For a real inductor, there is always some losses and that can be used to define a time...
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