High Speed, Unipolar Sine Inverter?

LowQCab

Joined Nov 6, 2012
4,029
And also, the now apparent fact that a 50% DC-Offset on a 100Khz Sine-Wave is actually correct.

This is a highly irregular request,
and so,
the reasons-why for these preliminary specifications become all that much more important,
no assumptions can be made.

It's entirely possible that there is a substantial miscommunication, or misunderstanding at play.

This, therefore,
requires a rather in-depth understanding of the operating principles of the Load
before a Circuit can be designed to Power it, or Control it, correctly, and/or, adequately.
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tsan

Joined Sep 6, 2014
138
So the Coilcraft technician who told me that their coupled inverter supports a unipolar pulse is wrong?
Pulse is a one time event and if the pulse time is short enough their coupled inductor supports it. The problem is that a long time unipolar pulse or sustainable unipolar voltage like given in the initial post (was at least there earlier) tends to saturate the core. Inductance drops in core saturation. There is a graph "Typical L vs Current" in the Coilcraft inductor datasheet.

I thought an inductor responds to change in current, not necessary to alternate between positive and negative.
As long as there is no core saturation that is true. In many practical applications (like a flyback converter mentioned in the inductor datasheet) volt-second balance has to be ensured by design in order to avoid core saturation.
 

ronsimpson

Joined Oct 7, 2019
2,989
Green trace is the output of V1, red trace is the output of the LC filter.
V1 is two MOSFETs. One pulls to +5V and the other pulls to 0V. L1 & C1 is a simple 100khz low pass filter.
This circuit is very dependent on what the load is.
1679491261500.png
 

Thread Starter

johnyradio

Joined Oct 26, 2012
434
Green trace is the output of V1, red trace is the output of the LC filter.
V1 is two MOSFETs. One pulls to +5V and the other pulls to 0V. L1 & C1 is a simple 100khz low pass filter.
This circuit is very dependent on what the load is.
View attachment 290432
An RC filter.
When you say "dependent on load", do you mean the cutoff freq changes with load current?

i think to support 25W it would require a resistor that's much too large for my application.
1679502582733.png

Later, I need to scale up the device to 100W or more, so i think a switching solution is needed.

Maybe a filtered square could be a controller for a power semiconductor?
 

Thread Starter

johnyradio

Joined Oct 26, 2012
434
I'm still obligated to resolve @LowQCab 's questions.

Meantime, some ideas:

Sine Driver
The EGS002 circuit isn't as simple as i'd like, and limited to 60 Hz. I wonder if there's a high-freq sine driver?
https://cxem.net/pitanie/files/5-389_EGS002_manual_en.pdf


Multilevel
There are some clever multilevel implementations which reduce number of switches.
https://core.ac.uk/download/pdf/212980526.pdf


Class D
Use a Class D amplifier as an SMPS, driven with a sinewave. 25W+ Class D amplifier chips and modules are plentiful and cheap.

"A Class-D amplifier is a switch-mode power supply (SMPS)."
https://www.eevblog.com/forum/projects/class-d-amplifier-as-four-quadrant-power-supply-stupid-idea/

"A bipolar (positive and negative, not transistor type) output class-D amplifier can make a great output stage for a 4 quadrant power supply." "Think of Class D amps as being similar to a switch-mode power supply, but with audio signals modulating the switching action."
https://www.extron.com/article/ts122001


Single Switch
For a unipolar sine, i think we don't need a full or even half H bridge. Maybe it could be 1 sine osc, 1 pwm generator, and 1 mosfet. Depending on whether an analog or digital sine is needed, the sine driver could be a filtered square wave, a cheap uC, or a sinewave lookup-table with a counter.
 
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RPLaJeunesse

Joined Jul 29, 2018
252
To minimize design effort consider a (whatever is appropriate) supply of 5V DC, followed by a "resonant Royer" (aka Baxandall) power oscillator producing 10Vp-p. Yes, a custom transformer is needed, but not all that difficult to get. Put the oscillator secondary in series with the DC supply, and get the desired 10Vp-p 100kHz with a +5V offset. https://en.wikipedia.org/wiki/Royer_oscillator

I would note that the resulting signal is unipolar, but it is not DC, as DC implies a relatively constant voltage. Ideally the signal has a relatively constant amplitude, but a voltage varying at 100kHz.
 

LowQCab

Joined Nov 6, 2012
4,029
All this meaningless discussion, blah, blah, blah, blah, blah.........

No Load/Device requires a Sine-Wave with a 50% DC-Offset, especially at 100khz ...........
MAKE ME WRONG.
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