Multiple signals on single Serial TX line

[Klaus Kragelund]

Even simpler. See...



http://www.analog-innovations.com/SED/Klaus_Combiner_2.pdf



It occurred to me that the screen for Other_Sig could be used to blank

the offending burble in TX_Output.



(I had no model for an analog switch... the VSwitch shown is 100 Ohms

on, 10Meg off.)

Reduces bost cost and occupied area, great

Regards

Klaus

 

[josephkk]

Lower capacitance and space reduction can be athieved with a coreless PCB xformer, although it needs to be subjected to a higher frequency to reduce magnetizing losses.

Cheers

Klaus

Concept check. How can there be magnetizing losses without a core to be
magnetized?

?-)

 

[Tim Williams]

Concept check. How can there be magnetizing losses without a core to be

magnetized?

Well, I suppose eddy currents in the windings will be lossy, and count as
magnetizing (i.e., acts like a parallel impedance).

If you stretch the scope to include the system (so, the transformer and
its driver), whatever handles the reactive current (capacitor or inverter)
will also have some losses, and one could define "magnetizing losses" as
that which is a direct result of the magnetizing current, and wouldn't
have existed if the winding had very high inductance, as with a core.

Example: single transistor forward converter. When the switch is on, flux
is stored in the transformer (while the load current is doing its thing).
When the switch turns off, a source of restoring flux is required.
Usually, the transformer's self inductance provides this; the flyback
pulse is clamped, and the energy either dissipated (RCD peak snubber) or
recycled (CT primary, one side switch, other side diode). Now consider
what happens as the transformer's self inductance is dropped: load current
remains constant, but magnetizing current rises, which puts more current
into the flyback pulse. Flux is still conserved, but reactive power is
much higher. You can see, if the inductance is so low that more
magnetizing current is drawn than load current, the switch and diode must
be beefed up significantly, and losses rise accordingly. It would be fair
to attribute these losses to magnetizing, as long as one emphasizes that
it's a system measure, not the transformer alone.

Tim

 

[Klaus Kragelund]

magnetized?



Well, I suppose eddy currents in the windings will be lossy, and count as

magnetizing (i.e., acts like a parallel impedance).

Isn't that the definition, that magnetizing current is the current that inherently must exist for a transformer to function? (so it does not matter if the core is present or not)

I'm working in low power these days, often the magnetizing current for those designs are higher than the reflected currents (secondary current)

Cheers

Klaus

 

[Joerg]

Isn't that the definition, that magnetizing current is the current
that inherently must exist for a transformer to function? (so it does
not matter if the core is present or not)

I'm working in low power these days, often the magnetizing current
for those designs are higher than the reflected currents (secondary
current)

Just make it a habit to only work on blustery days because then there is
enough wind for some more power

Core-less or "air core" look mostly just nice on paper. In reality
ferrite often wins. Reason is that the leakage inductance is
substantially higher without a core and also the required higher
frequency leads to some other losses that add in. And for dessert there
will usually be assorted EMC headaches.

 

[Tim Williams]

Core-less or "air core" look mostly just nice on paper. In reality
ferrite often wins. Reason is that the leakage inductance is
substantially higher without a core and also the required higher
frequency leads to some other losses that add in. And for dessert there
will usually be assorted EMC headaches.

I once contemplated using in-board (planar) coils for a particular
inverter snubber circuit. But trying to do that while keeping the board
profile less than gargantuan doesn't really make sense; add to that the
difficulty of routing gate signals to said inverter around these loops!

Tim

 

[josephkk]

magnetized?

Well, I suppose eddy currents in the windings will be lossy, and count as
magnetizing (i.e., acts like a parallel impedance).

If you stretch the scope to include the system (so, the transformer and
its driver), whatever handles the reactive current (capacitor or inverter)
will also have some losses, and one could define "magnetizing losses" as
that which is a direct result of the magnetizing current, and wouldn't
have existed if the winding had very high inductance, as with a core.

Example: single transistor forward converter. When the switch is on, flux
is stored in the transformer (while the load current is doing its thing).
When the switch turns off, a source of restoring flux is required.
Usually, the transformer's self inductance provides this; the flyback
pulse is clamped, and the energy either dissipated (RCD peak snubber) or
recycled (CT primary, one side switch, other side diode). Now consider
what happens as the transformer's self inductance is dropped: load current
remains constant, but magnetizing current rises, which puts more current
into the flyback pulse. Flux is still conserved, but reactive power is
much higher. You can see, if the inductance is so low that more
magnetizing current is drawn than load current, the switch and diode must
be beefed up significantly, and losses rise accordingly. It would be fair
to attribute these losses to magnetizing, as long as one emphasizes that
it's a system measure, not the transformer alone.

Tim

Wow, that would be a big stretch.
Just the same down thread i read about adding cores, in that case it would
make sense.

?-)

 

[josephkk]

Isn't that the definition, that magnetizing current is the current that inherently must exist for a transformer to function? (so it does not matter if the core is present or not)

I'm working in low power these days, often the magnetizing current for those designs are higher than the reflected currents (secondary current)

Cheers

Klaus

Well a quick check came up with hysteresis losses which requires a core
material to be magnetized, and eddy current losses which also require a
core that can conduct. I doubt that megnetoconstriction can be usefully
applied here.

But is also appears that cores are possible.

?-)

 

[Klaus Kragelund]

Just make it a habit to only work on blustery days because then there is

enough wind for some more power



Core-less or "air core" look mostly just nice on paper. In reality

ferrite often wins. Reason is that the leakage inductance is

substantially higher without a core and also the required higher

frequency leads to some other losses that add in. And for dessert there

will usually be assorted EMC headaches.

A couple of years ago I made a converter with coreloss spiral windings, had efficiency of 65+% (in ressonance) and had no problems passing the EMC

Many are afraid of the EMC, but it's often exaggerated. The size of the transformer is close to 1000 times less than the wavelenght and as such the spiral transformer is a very low efficiency antenna.

Cheers

Klaus

 

[Joerg]

A couple of years ago I made a converter with coreloss spiral
windings, had efficiency of 65+% (in ressonance) and had no problems
passing the EMC

Many are afraid of the EMC, but it's often exaggerated. The size of
the transformer is close to 1000 times less than the wavelenght and
as such the spiral transformer is a very low efficiency antenna.

Well, even the super tiny transformers in some of the AD isolated
converters have given us the blues. At one client we had to redesign
that part of the circuitry to get it through class B. But class B is
still fairly easy, at least when compared to aerospace requirements.

 

[Joerg]

Well a quick check came up with hysteresis losses which requires a core
material to be magnetized, and eddy current losses which also require a
core that can conduct. I doubt that megnetoconstriction can be usefully
applied here.

But is also appears that cores are possible.

Ferrite is a nice material. After all, we've built sensitive receivers
with it in there for decades