Mosfet operation

[Claude Abraham]

Hi,


Actually, a transformer can be used for any of these:

1. voltage controlled voltage source
2. current controlled current source
3. voltage controlled current source
4. current controlled voltage source

Which one do we choose?

Well, most generally, the transformer is a POWER converter.
It takes one form of power and converts it to another.
It's only after it's been inserted into a particular circuit that
it may take on a new meaning, such as "current transformer".
Of course there are also transformers manufactured with
an intended end application and are so named as such,
but that doesnt mean they have to be used that way either,
or i should say that doesnt mean that they WILL be used
in that way because after all, their operation is more
flexible than that as they cant really be truely classified
that way.

The basic operation requires current to generate a magnetic
field, so we might be tempted to call the primary a
'current controlled magnetic source', but then we would
have to call the secondary a 'magnetically controlled current source'
because it is not current that causes current in the output,
it's the changing magnetic field.

I'm a little puzzled. Nos. 1 & 2 look fine to me. A voltage controlled voltage source, and a current controlled current source are easily achieved w/ xfmrs. The turns ratio is the scaling parameter.

But you've lost me with nos. 3 & 4. How does a primary voltage get translated into a secondary current source? Or vice-versa? A xfmr does not gyrate I & V.

As far as what "causes" (I don't think in terms of cause-effect) the secondary current, I don't think it is the magnetic field only. Rather, a time-changing magnetic field is always accompanied by a time-changing electric field. Please don't ask me which is the cause or effect, because the question is moot. E and H cannot exist independently under time-changing conditions. This E field has curl (rotation) and free charges in a conducting loop will move under the influence of E and H. H acts normally to charge motion whereas E acts tangentially.

As far as requiring current to generate a magnetic field, voltage is also required. H fields store energy and energy is the product of power and time. Power is I*V, so if P is non-zero, I and V are non-zero. Both Vp & Ip are needed to establish H.

Does this help? BR.

 

[Hero999]

You've posted this kind of thing before but I don't think it's correct. A transformer is always a voltage to voltage converter or current to current converter as far as I'm concerned.

You do get current transformers but you have to add a burden resistor. All a current transformer is doing is matching the impedance of the resistor to the cable going through it. For example if the burden resistor is 160mΩ and the current transformer has 16384 turns the impedance seen by the wire would be [latex]\frac{160\times 10^{-3}}{\sqrt{16384}}=1.25 \times 10^{-3}\Omega[/latex] = 12.5mΩ.

 

[Claude Abraham]

You've posted this kind of thing before but I don't think it's correct. A transformer is always a voltage to voltage converter or current to current converter as far as I'm concerned.

You do get current transformers but you have to add a burden resistor. All a current transformer is doing is matching the impedance of the resistor to the cable going through it. For example if the burden resistor is 160mΩ and the current transformer has 16384 turns the impedance seen by the wire would be [latex]\frac{160\times 10^{-3}}{\sqrt{16384}}=1.25 \times 10^{-3}\Omega[/latex] = 12.5mΩ.

Are you addressing moi?

If so, I've stated just what you have stated. A xfmr is I to I and V to V as far as action goes. A current xfmr, or CT, can function just fine w/o a burden resistor. When not taking measurements, shorting the secondary with 0 ohms works just fine.

All xfmrs have one I controlled by another, and likewise for V. The main difference betwen CT & VT is that with a VT, Vp is fixed by the voltage source driving the primary, and Vs is controlled by Vp. Then, Is is given by Ohms law, Is = Vs/Rs. Ip is thus controlled by Is.

With a CT, Ip is fixed, and Is is controlled by Ip. Vs is determined by Is and Rs, the "burden resistor". Vp is then controlled by Vs.

In all cases, CT or VT, one primary quantity is fixed. It's counterpart on the secondary is controlled. Then Ohms law determines the other secondary quantity, which controls its primary counterpart.

It's pretty simple.

 

[Hero999]

I was addresing MrAl, I should've included a quote.