Re: Multi-cycle current control
Thanks, Ron, but MCC is what the industry
uses; I don't have an opportunity to change that. I'm sure they
looked at 'magic sine waves'.
On 2023-07-28 17:01, ron davison wrote:
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If your trying to reduce harmonics and edge rate
generated frequencies, would not the EMI be reduced iff
switching the max current only after having the meduim current
on before an on event or off to on for an off event of max
current source. You can aproximate a sine wave as best as
pssoible with the sequence?
Low, mis, mid?+ low, high, high?+ low, high?+ mid, high?+
mid?+ low. then reverse ands tep down to complet 1st 1/2 wave.
Then repeat for negtive AC half cycle input.
This would give the lowest EMI. If this was set as
aproximate load point, then any fine temp adjustments would
not add to much surge currents.
On Fri, Jul 28, 2023 at
4:25?AM John Woodgate < jmw@...>
wrote:
I uploaded a graph to Photos.The graph
shows the current and voltage waveforms for an example
of 3-cycle control, typically used for supplying heaters
that need fine temperature control. I want to generate
that current waveform in LTspice to look at its
spectrum.
I need help to specify the current
waveform, presumably as a BI source. All assistance
gratefully acknowledged.
--
Ron Davison
principle
Efficient
Electronic Solutions
760.505.4380
“What
I cannot build, I do not understand”?Richard
Feynman?
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Re: Multi-cycle current control
If your trying to reduce harmonics and edge rate generated frequencies, would not the EMI be reduced iff switching the max current only after having the meduim current on before an on event or off to on for an off event of max current source. You can aproximate a sine wave as best as pssoible with the sequence? Low, mis, mid?+ low, high, high?+ low, high?+ mid, high?+ mid?+ low. then reverse ands tep down to complet 1st 1/2 wave. Then repeat for negtive AC half cycle input. This would give the lowest EMI. If this was set as aproximate load point, then any fine temp adjustments would not add to much surge currents.
On Fri, Jul 28, 2023 at 4:25?AM John Woodgate < jmw@...> wrote:
I uploaded a graph to Photos.The graph shows
the current and voltage waveforms for an example of 3-cycle
control, typically used for supplying heaters that need fine
temperature control. I want to generate that current waveform in
LTspice to look at its spectrum.
I need help to specify the current waveform,
presumably as a BI source. All assistance gratefully
acknowledged.
-- Ron Davison principle Efficient Electronic Solutions 760.505.4380
“What I cannot build, I do not understand”?Richard Feynman?
|
Re: Multi-cycle current control
You are right; It's 3.33 Hz. I didn't have
grid lines enabled. Your Waveform settings are very different
from mine, but I can cope.
On 2023-07-28 15:58, Andy I wrote:
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5 Hz?? Where does that come from?
The requested waveform repeats every 0.06 ms --> 16.67 Hz.? Is
there something that happens beyond the 0.12 s window you showed
us?
LTspice's FFT shows me a component at 3.33 Hz but it's about 80 dB
below the fundamental.? I saw nothing at 5 Hz.
Andy
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Re: Multi-cycle current control
5 Hz?? Where does that come from?
The requested waveform repeats every 0.06 ms --> 16.67 Hz.? Is there something that happens beyond the 0.12 s window you showed us?
LTspice's FFT shows me a component at 3.33 Hz but it's about 80 dB below the fundamental.? I saw nothing at 5 Hz.
Andy
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Re: Multi-cycle current control
Yes, I did that. But the lowest frequency
component is 5 Hz, admittedly quite small.
On 2023-07-28 15:39, Andy I wrote:
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John wrote, "I want to generate
that current waveform in LTspice to look at its spectrum."
As you may discover, the spectrum looks better (and/or easier to
understand at frequencies < 50 Hz) if you run the simulation
for several more cycles.? For example, 1200 ms instead of 120 ms.?
It needs to be an integer multiple of 60 ms.? 16.7 Hz = lowest
frequency.
Andy
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Re: Multi-cycle current control
Thanks very much, Andy.
On 2023-07-28 15:10, Andy I wrote:
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John,
I uploaded "3-cycle symmetry.asc" to the Temp folder.? It
generates the waveform in your photo "3-cycle symmetry.jpg" in the
photo
album.
It could be done other ways.? Also, I could have parameterized
more, but I kept that part of it simple.
Andy
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Re: Multi-cycle current control
John wrote, "I want to generate that current waveform in LTspice to look at its spectrum."
As you may discover, the spectrum looks better (and/or easier to understand at frequencies < 50 Hz) if you run the simulation for several more cycles.? For example, 1200 ms instead of 120 ms.? It needs to be an integer multiple of 60 ms.? 16.7 Hz = lowest frequency.
Andy
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Re: Multi-cycle current control
John, I uploaded "3-cycle symmetry.asc" to the Temp folder.? It generates the waveform in your photo "3-cycle symmetry.jpg" in the photo album. It could be done other ways.? Also, I could have parameterized more, but I kept that part of it simple. Andy
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Re: Multi-cycle current control
John asked for assistance generating a gated sinewave.
Start with a continuous SINE wave (V-source) and a PULSE wave (another V-source, an offset square wave), then use a B-source to multiply the two waveform voltages.
Andy
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Re: Reflected power in RF power supplies
Tony wrote, "... a function of the source impedance. Since this is never specified, ...".
Sometimes it is.? There might be s parameters, or an output port reflection coefficient, or something like that.? But you're right, it is often not specified.
I guess it might depend on the market into which the RF amplifier is being sold.? There are applications for which knowing the output's source impedance (or the goodness of that match) is quite important, and so they have a datasheet spec for it.
Andy
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Re: Reflected power in RF power supplies
minsun wrote, "They do not understand the physics."
That's possible.? But it's also possible that they understand it very well, and it's just a problem of misunderstanding what the other person says.? I think it's likely the manufacturer knows the physics quite well, since they know how to design these power amps.? On the other hand the answers may have come from marketing people or applications specialists who indeed might not know.
Andy
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Multi-cycle current control
I uploaded a graph to Photos.The graph shows
the current and voltage waveforms for an example of 3-cycle
control, typically used for supplying heaters that need fine
temperature control. I want to generate that current waveform in
LTspice to look at its spectrum.
I need help to specify the current waveform,
presumably as a BI source. All assistance gratefully
acknowledged.
|
Re: Reflected power in RF power supplies
Yes, RF power amplifiers are often implicitly specified for a load
of 50Ω, but in general, the source impedance of such an amplifier
will not be 50Ω, as that would limit its efficiency to less than
50%.
The power absorbed in the source as a result of a reflection due to
a mismatched load would be a function of the source impedance. Since
this is never specified, the user has no way of knowing what any
dissipated "reflected power" would be.
The proper way of specifying this aspect of PA performance is by
quoting a maximum VSWR of the load (relative to the nominal load
impedance - assumed to be 50Ω) that the amplifier is guaranteed to
tolerate, without damage. This is roughly similar to the notion for
SOA (Safe Operating Area) for audio amplifiers. It amounts to the
same thing: the load line that the amplifier sees.
--
Regards,
Tony
On 28/07/2023 08:32, francesco_angelin
via groups.io wrote:
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Hi Tony, I
perfectly agree with you! Nevertheless, let take into account that
in the RF world, quite often the term "Power" actually means
"voltage", and the measure is given in dBm, referred to the
standard 50 Ohm impedance. In case the impedance is 75 Ohm, it is
clearly stated. Generators with 0 Ohm are not existing and would
be not practical.
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Re: Reflected power in RF power supplies
Hi Tony, I perfectly agree with you! Nevertheless, let take into account that in the RF world, quite often the term "Power" actually means "voltage", and the measure is given in dBm, referred to the standard 50 Ohm impedance. In case the impedance is 75 Ohm, it is clearly stated. Generators with 0 Ohm are not existing and would be not practical.
Regards!
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Re: Reflected power in RF power supplies
Hello, minus -
Here is an example that shows how this reflected power idea works. It does NOT rely on transmission lines, at all. In fact, it works at DC. It is a little odd because DC supplies are rarely used this way, but the principles apply.
1. Suppose that you have a DC power supply with a 50 ohm source impedance and delivering 100V unloaded. This almost never happens in real life but it is quite “legal” electrically.
2. Now suppose we put a 50 ohm load on the output side of the source impedance.
3. The power supply now has a net 100 ohms load and provides 1 ampere into the source resistor and the load resistor. Each resistor will have 50V across it.
4. Each resistor, the source resistor will dissipate 50Watts (50V * 1A). Remember, this is DC.
5. Now, lets change the load to 40 ohms.
4. The power supply has a total load of 90 ohms and an output current of 1.11 Amps. The 40 ohm load resistor now has a voltage drop of 44.44V and dissipates 49.33W .
5. As we would expect, this power is less than the “matched” case. On of the ways of “explaining” this loss of power in the load resistor is to think that the power supply and source resistor really are delivering 50W but that 0.67W are “reflected” by the load, back into the supply. We know, however, that this is an artificial idea, as there is no actual "reflected power”. None the less, this is exactly how the term reflected power applies in your situation.
6.It is a slightly different matter with an AC supply in which the load can be reactive. Then, the load current is out of phase with the source voltage an there CAN be serious problems. Again, there might not be any actual reflected power, but it is a useful idea that can be use to describe operating limits for the amplifier.
Jim
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I did. I am not satisfied with their answers. They do not understand the physics.
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Re: Reflected power in RF power supplies
I did. I am not satisfied with their answers. They do not understand the physics.
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Re: Reflected power in RF power supplies
Have you tried asking the manufacturer? They are the ones that
can answer your question, much better than our conjectures.
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Thanks for all replies.?This question is off topic but I do not
know any group or forum that that have such experienced and
generous users. This group is indeed a great treasure!
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Re: Reflected power in RF power supplies
Thanks for all replies.?This question is off topic but I do not know any group or forum that that have such experienced and generous users. This group is indeed a great treasure!
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Re: Can't see the noise of a white noise generator
#NOISE
marcel wrote, "Is LTspice deterministic? For large simulations that have difficulty converging?"
Yes.? And that even could be one of the reasons why it has difficulty converging (no randomness that could divert it away from the point of difficulty).
Andy
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Re: 'SYMBOL ind X Y R90' directive in asc file, possible bug in 17.1.9 ?
Start a new blank simulation and just add an
inductor. Does it look correct? If not, the symbol file is
corrupted. If you can find it at
:C:\Users\{You]\AppData\Local\Programs\ADI\LTspice\lib.zip\lib\sym
you may be able to substitute a correct symbol from an earlier
version of LTspice (but not TOO early).
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By 'the circuit not rendering' : I meant the circuit did not show
at all. a blank draft.
Now when testing on a new draft and adding an inductor, the symbol
of the inductor does not render properly with like one full circle
plus three quarters of another circle. while other standard
symbols render ok.
So it's more graphics related.
That's seems a very strange bug. Maybe not ltspice per se but some
2D vector rendering library problem, or some Windows display UI
system settings interfering. but since other symbols render ok, i
am perplexed.
Will submit to analog.com
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John Woodgate
Tony Casey