Devil's Staircase

On Sat, 01 Jun 2019 08:23:01 -0700, John Larkin
<jjlarkin@highlandtechnology.com> wrote:

On Sat, 1 Jun 2019 00:42:55 -0400, bitrex <user@example.net> wrote:

On 6/1/19 12:23 AM, bitrex wrote:
On 5/31/19 10:55 PM, John Larkin wrote:
On Fri, 31 May 2019 22:22:37 -0400, krw@notreal.com wrote:

On Fri, 31 May 2019 15:36:39 -0700, John Larkin
jjlarkin@highland_snip_technology.com> wrote:



I want to make a class-D audio amp, 150 watts or so, using a TI
TPA3255 maybe. It's good for 600 watts mono!

I'll use it full-bridge to drive a step-up transformer, probably a
custom toroid. But toroids are especially unhappy with any DC drive,
and the class D part will surely have some DC offset. The TI spec is
60 mV max output offset, which could be a problem into a good
transformer. Speakers don't mind a little DC, but transformers do. DC
can cause stairstepped increase in circulating current, the Devil's
Staircase, until they saturate.

So I'm thinking I'll add a series blocking cap so I can ignore any DC
problems. It will have to be big, 10s of millifarads at least. Biggest
thing on the board. Maybe use a low voltage electrolytic with
antiparallel power diodes, or a shorted bridge, to protect it from
accidental forward or backwards over-voltage.

Lytics will be big, and supercaps don't seem to like ripple current. I
think.

Any other ideas about driving a transformer from an audio amp?

Feed back a (heavily) filtered signal to the input?  The problem is
that they don't really tell you what the input of the 3255 looks like,
IIRC (none do).  It's intended to be AC coupled.

TI does spec 60 mV max DC offset at the output, which is pretty good,
but even that could push a lot of DC into my transformer.

There is probably some way to tweak the input with a little DC.
Feedback loop or even a trimpot.



You can drive the transformer bridged but using current-sense feedback
instead of voltage feedback; put a small sense resistor in line with
each amp output going to each end of the transformer and take off the DC
feedback to the opposite amp from the junction. That way the amps should
act as their own servo to keep DC out of the transformer.

Lower power example like this for driving audio isolation transformer
for XLR cable:

https://www.dropbox.com/s/8d1flmr8lko2nf1/Screenshot_2019-06-01_00-12-49.png?dl=0



In the case of the TPA3255 I think you would put a low-offset op amp in
front of the inputs and AC couple into that and do something similar but
the 3255 just acts as a power buffer, I don't immediately see anything
in the datasheet that says you can't intentionally apply a small DC
feedback generated offset to its single input per channel as an error
signal.

It's not stated how the normally AC coupled inputs affect the DC
offset, but we have the eval board and I could have a scut bunny set
it up and try it.

One trimpot and 30 seconds of tech time, to turn it, is sure
appealing. If it turns out we don't need it, we can leave it off the
board.

I don't think you can count on that, long term. I think you're going
to need something to servo the voltage to zero.

The input resistance of the TPA3255 is 10K, and they want 10 uF input
coupling caps. Tau is 100 ms, which is 1.6 Hz corner. That suggests to
me that the input caps are also used as lowpass filters for the DC
feedback loop, which then suggests we could push the input pins gently
to change the output offset.

Datasheets tend to hide the good stuff.

That was my point. They really don't tell you what's going on. A few
years ago, I wanted to DC couple an audio amp but couldn't get them
(any of the manufacturers) to fork over the designs. We buy tons of
these things but none were interested in showing us the details.

 

[Jan Panteltje]

On a sunny day (Sat, 01 Jun 2019 07:23:04 -0700) it happened Joerg
<news@analogconsultants.com> wrote in <glfg1pFo3i8U1@mid.individual.net>:

On 2019-05-31 22:08, Jan Panteltje wrote:
On a sunny day (Fri, 31 May 2019 15:36:39 -0700) it happened John Larkin
jjlarkin@highland_snip_technology.com> wrote in
q4a3fe9nlmflqfmadlb1dbfrtg7slvr7f0@4ax.com>:



I want to make a class-D audio amp, 150 watts or so, using a TI
TPA3255 maybe. It's good for 600 watts mono!

I'll use it full-bridge to drive a step-up transformer, probably a
custom toroid. But toroids are especially unhappy with any DC drive,
and the class D part will surely have some DC offset.

As somebody else already pointed out, maybe a DC control loop could zero the current.


That's what I'd do. No output cap, much smaller, much cheaper.


Not so easy, low pass, some opamps, but not impossible.


It is quite easy if you use that same loop for everything, DC as well as
drive signal. That's how I do it with class D stuff. Mine have also
always driven weird loads, not speakers. Use another opamp up front that
has very low offset.

It would be good to have that blessed by TI, to make sure the analog
loop filter in the IC doesn't become upset.


The idea of supercaps is nice, maybe I should order some to see how those
perform in a similar application (driving cryo cooler here).
The ebay class D unit did not like the step up transformer... and died.


Be careful not to get into a resonant mode at some frequency. That can
hammer them, they see an output AC short, become instable like an opamp
with a capacitive load and potentially croak.

No worry, I am making 60 Hz (almost)
http://panteltje.com/pub/cryocooler_vibration_damper_side_view_img_2583.jpg
for the cry-cooler, that is the mechanical resonance of the plunger in it.
Moves like this:
https://www.google.nl/search?dcr=0&q=FreePistonsterling.jpg.&tbm=isch&source=hp&sa=X&ved=2ahUKEwjv5dDm0cjiAhXGPFAKHT9FDpIQsAR6BAgAEAE&biw=1670&bih=854#imgrc=JzxBQ21xfCh2JM:&spf=1559404338866
Could be on the mains with a variac in the US (soem did that)
but in Europe we have 50 Hz.
Using a 50 Hz power transformer in reverse on the audio amp output.

The normal class B audio amps with output coupling caps work fine for that.


Not always. You were probably lucky. I had the overcurrent trip come on
a regular big old stereo amp when I drove a load capacitively for
aerospace testing.

This one never failed me in all those years :
http://panteltje.com/panteltje/amplifier/index.html
from year 2000!

I have some bigger stuff too...

It is not so critical, I have the original switch mode board too, and it works,
but is difficult to control.

 

On Saturday, 1 June 2019 03:22:53 UTC+1, k...@notreal.com wrote:

On Fri, 31 May 2019 15:36:39 -0700, John Larkin
jjlarkin@highland_snip_technology.com> wrote:

I want to make a class-D audio amp, 150 watts or so, using a TI
TPA3255 maybe. It's good for 600 watts mono!

I'll use it full-bridge to drive a step-up transformer, probably a
custom toroid. But toroids are especially unhappy with any DC drive,
and the class D part will surely have some DC offset. The TI spec is
60 mV max output offset, which could be a problem into a good
transformer. Speakers don't mind a little DC, but transformers do. DC
can cause stairstepped increase in circulating current, the Devil's
Staircase, until they saturate.

So I'm thinking I'll add a series blocking cap so I can ignore any DC
problems. It will have to be big, 10s of millifarads at least. Biggest
thing on the board. Maybe use a low voltage electrolytic with
antiparallel power diodes, or a shorted bridge, to protect it from
accidental forward or backwards over-voltage.

Lytics will be big, and supercaps don't seem to like ripple current. I
think.

Any other ideas about driving a transformer from an audio amp?

Feed back a (heavily) filtered signal to the input? The problem is
that they don't really tell you what the input of the 3255 looks like,
IIRC (none do). It's intended to be AC coupled.

I was wondering that, RC the transformer drive & feed back with greater gain. Trouble is if the load ever has a rectified component, your amp is toast. There's a reason these kinda things are usually done with valves.


NT

 

[John Larkin]

On Sat, 1 Jun 2019 10:32:19 -0700 (PDT), tabbypurr@gmail.com wrote:

On Saturday, 1 June 2019 03:22:53 UTC+1, k...@notreal.com wrote:
On Fri, 31 May 2019 15:36:39 -0700, John Larkin
jjlarkin@highland_snip_technology.com> wrote:

I want to make a class-D audio amp, 150 watts or so, using a TI
TPA3255 maybe. It's good for 600 watts mono!

I'll use it full-bridge to drive a step-up transformer, probably a
custom toroid. But toroids are especially unhappy with any DC drive,
and the class D part will surely have some DC offset. The TI spec is
60 mV max output offset, which could be a problem into a good
transformer. Speakers don't mind a little DC, but transformers do. DC
can cause stairstepped increase in circulating current, the Devil's
Staircase, until they saturate.

So I'm thinking I'll add a series blocking cap so I can ignore any DC
problems. It will have to be big, 10s of millifarads at least. Biggest
thing on the board. Maybe use a low voltage electrolytic with
antiparallel power diodes, or a shorted bridge, to protect it from
accidental forward or backwards over-voltage.

Lytics will be big, and supercaps don't seem to like ripple current. I
think.

Any other ideas about driving a transformer from an audio amp?

Feed back a (heavily) filtered signal to the input? The problem is
that they don't really tell you what the input of the 3255 looks like,
IIRC (none do). It's intended to be AC coupled.

I was wondering that, RC the transformer drive & feed back with greater gain. Trouble is if the load ever has a rectified component, your amp is toast. There's a reason these kinda things are usually done with valves.


NT

PM alternators often drive shunt regulators, triacs or mosfets. We
have to tolerate that.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Phil Allison]

John Doe wrote:

Isn't most audio power class D now?

My powered computer speakers JBL LSR305 Studio Monitors use class D
amplifiers.

** Hardly proves the point about numbers but here is a link to some interesting technical stuff on that model.

http://rdimitrov.twistedsanity.net/blog/show.php?entry=JBL%20LSR305%20Teardown%20and%20Analysis



..... Phil

 

[Cursitor Doom]

On Sat, 01 Jun 2019 09:27:54 -0700, John Larkin wrote:

The problem is that the DeLoreans are getting hard to find.

ebay has an '82 for $40K.

There were not that many made before JdL got taped by the FBI drooling
over the prospect of a massive cocaine deal.



--
This message may be freely reproduced without limit or charge only via
the Usenet protocol. Reproduction in whole or part through other
protocols, whether for profit or not, is conditional upon a charge of
GBP10.00 per reproduction. Publication in this manner via non-Usenet
protocols constitutes acceptance of this condition.

 

[Lasse Langwadt Christense]

søndag den 2. juni 2019 kl. 04.05.06 UTC+2 skrev John Larkin:

On Sat, 1 Jun 2019 18:50:48 -0700 (PDT), tabbypurr@gmail.com wrote:

On Saturday, 1 June 2019 17:36:48 UTC+1, John Larkin wrote:

We're selling a lab-grade voltage source, so we want the output to be
stiff. I estimated the 20 mohms primary DCR by scaling from a smaller
toroid that we have. The AC output impedance is a separate issue from
the DC primary current hazard.

We will be sensing output current to control the complex output
impedance, so we can in theory tune the box Zout to zero by canceling
the transformer impedance. That approaches building an oscillator, but
we might take out some of the native impedance.

But alternators are very inductive, and our main goal is to simulate
alternators.

How do you intend to simulate the voltage spike when they suddenly reduce load?


NT

A bit of our simulated inductance will be a real inductor. It can do
the fast stuff, and our DSP loop can take over behind that.

It's similar to making a super-wideband inductor by making a series
string of little and big inductors. People do that in bias tees and
such.

The real-life load on the alternator will probably be shunt regulator,
bridge rectifier, capacitor, so really fast spikes probably wouldn't
matter much.

We're trying to get them to lend us an alternator. We could spin that
somehow and see how it behaves.

https://youtu.be/D4DqyElNFAs

 

[John Larkin]

On Sat, 1 Jun 2019 18:50:48 -0700 (PDT), tabbypurr@gmail.com wrote:

On Saturday, 1 June 2019 17:36:48 UTC+1, John Larkin wrote:

We're selling a lab-grade voltage source, so we want the output to be
stiff. I estimated the 20 mohms primary DCR by scaling from a smaller
toroid that we have. The AC output impedance is a separate issue from
the DC primary current hazard.

We will be sensing output current to control the complex output
impedance, so we can in theory tune the box Zout to zero by canceling
the transformer impedance. That approaches building an oscillator, but
we might take out some of the native impedance.

But alternators are very inductive, and our main goal is to simulate
alternators.

How do you intend to simulate the voltage spike when they suddenly reduce load?


NT

A bit of our simulated inductance will be a real inductor. It can do
the fast stuff, and our DSP loop can take over behind that.

It's similar to making a super-wideband inductor by making a series
string of little and big inductors. People do that in bias tees and
such.

The real-life load on the alternator will probably be shunt regulator,
bridge rectifier, capacitor, so really fast spikes probably wouldn't
matter much.

We're trying to get them to lend us an alternator. We could spin that
somehow and see how it behaves.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

On Saturday, 1 June 2019 19:30:42 UTC+1, John Larkin wrote:

On Sat, 1 Jun 2019 10:32:19 -0700 (PDT), tabbypurr wrote:
On Saturday, 1 June 2019 03:22:53 UTC+1, k...@notreal.com wrote:
On Fri, 31 May 2019 15:36:39 -0700, John Larkin
jjlarkin@highland_snip_technology.com> wrote:

I want to make a class-D audio amp, 150 watts or so, using a TI
TPA3255 maybe. It's good for 600 watts mono!

I'll use it full-bridge to drive a step-up transformer, probably a
custom toroid. But toroids are especially unhappy with any DC drive,
and the class D part will surely have some DC offset. The TI spec is
60 mV max output offset, which could be a problem into a good
transformer. Speakers don't mind a little DC, but transformers do. DC
can cause stairstepped increase in circulating current, the Devil's
Staircase, until they saturate.

So I'm thinking I'll add a series blocking cap so I can ignore any DC
problems. It will have to be big, 10s of millifarads at least. Biggest
thing on the board. Maybe use a low voltage electrolytic with
antiparallel power diodes, or a shorted bridge, to protect it from
accidental forward or backwards over-voltage.

Lytics will be big, and supercaps don't seem to like ripple current. I
think.

Any other ideas about driving a transformer from an audio amp?

Feed back a (heavily) filtered signal to the input? The problem is
that they don't really tell you what the input of the 3255 looks like,
IIRC (none do). It's intended to be AC coupled.

I was wondering that, RC the transformer drive & feed back with greater gain. Trouble is if the load ever has a rectified component, your amp is toast. There's a reason these kinda things are usually done with valves.


NT

PM alternators often drive shunt regulators, triacs or mosfets. We
have to tolerate that.

I'm wondering how you plan to do that with a toroidal, dc on the 2ndary having the same effect on the core as dc on the primary.


NT

 

On Saturday, 1 June 2019 17:36:48 UTC+1, John Larkin wrote:

We're selling a lab-grade voltage source, so we want the output to be
stiff. I estimated the 20 mohms primary DCR by scaling from a smaller
toroid that we have. The AC output impedance is a separate issue from
the DC primary current hazard.

We will be sensing output current to control the complex output
impedance, so we can in theory tune the box Zout to zero by canceling
the transformer impedance. That approaches building an oscillator, but
we might take out some of the native impedance.

But alternators are very inductive, and our main goal is to simulate
alternators.

How do you intend to simulate the voltage spike when they suddenly reduce load?


NT

 

On Saturday, 1 June 2019 16:38:01 UTC+1, John Larkin wrote:

On Fri, 31 May 2019 22:49:02 -0700 (PDT), whit3rd <whit3rd@gmail.com
wrote:

It would take a giant capacitor, easily the biggest thing on the
board. This is a nominal 400 Hz system, but we may as well go down to
50 Hz to have more market. I can just poke in a 33,000 uF cap per amp,
I guess.

Some folk may want to test with varying f to their 50Hz equipment, so lower may be better.

If this is for a three-phase power drive, a small three-phase motor with no
load is a great filter/flywheel/phase balance component. So, how much ripple
current is the blocking capacitor going to pass? The voltage should be kept low by the
parallel resistor, of course, and that means a 6V capacitor is overrated for the job.
Without blocking, you'd run DC into your three-phase loads (not recommended).

Do your AC loads burn up when given DC? Or, just magnetize and hum loudly?

We need to be frequency/voltage/phase agile, and we want to be able to
program complex output impedance. The point of this box is that the
customer wants to simulate alternators without spinning actual
alternators, which they certainly could.

Problem is, this customer likes us so they throw all the hard problems
at us, and we have to hope they'll buy 300, and not 3. I guess I
shouldn't complain about being furnished interesting problems.

so many load problems can occur. There's still a reason people use valves.


NT

 

On Sunday, 2 June 2019 03:05:06 UTC+1, John Larkin wrote:

On Sat, 1 Jun 2019 18:50:48 -0700 (PDT), tabbypurr wrote:
On Saturday, 1 June 2019 17:36:48 UTC+1, John Larkin wrote:

We're selling a lab-grade voltage source, so we want the output to be
stiff. I estimated the 20 mohms primary DCR by scaling from a smaller
toroid that we have. The AC output impedance is a separate issue from
the DC primary current hazard.

We will be sensing output current to control the complex output
impedance, so we can in theory tune the box Zout to zero by canceling
the transformer impedance. That approaches building an oscillator, but
we might take out some of the native impedance.

But alternators are very inductive, and our main goal is to simulate
alternators.

How do you intend to simulate the voltage spike when they suddenly reduce load?


NT

A bit of our simulated inductance will be a real inductor. It can do
the fast stuff, and our DSP loop can take over behind that.

It's similar to making a super-wideband inductor by making a series
string of little and big inductors. People do that in bias tees and
such.

The real-life load on the alternator will probably be shunt regulator,
bridge rectifier, capacitor, so really fast spikes probably wouldn't
matter much.

We're trying to get them to lend us an alternator. We could spin that
somehow and see how it behaves.

I'd think you'd need that to determine L, C etc.

Your app may have that load, but if you make it do under 50Hz it's going to get used for other tasks. Valves are inherently sledgehammerproof, as long as you add a spark gap. Many EEs have failed to achieve that with silicon. Dropping a heavy load on a shaker table could produce interesting 'signals'.


NT

 

On Sat, 01 Jun 2019 08:44:48 -0700, John Larkin
<jjlarkin@highlandtechnology.com> wrote:

Or how about a high inductance but low resistance external solenoid
across toroid primary ? Apparently the frequency is in the 400 Hz
ballpark, so even less solenoid inductance should suffice, compared to
50/60 Hz.

I'm guessing that the TI amp would fight to maintain its output offset
voltage. A series cap would be a lot easier. I could quit bitching and
use some big caps. Probably don't need the diodes.

The output LC LFPs are outside of any feedback loops, so the LPF
filter inductor DC resistances are in series with the load DC
resistances, thus limiting the DC current.

 

[Cursitor Doom]

On Sat, 01 Jun 2019 19:16:39 -0700, Lasse Langwadt Christensen wrote:

https://youtu.be/D4DqyElNFAs

There appears to be a cat wandering about under the engine. Surely that's
a safety fail?



--
This message may be freely reproduced without limit or charge only via
the Usenet protocol. Reproduction in whole or part through other
protocols, whether for profit or not, is conditional upon a charge of
GBP10.00 per reproduction. Publication in this manner via non-Usenet
protocols constitutes acceptance of this condition.

 

[Piglet]

On 01/06/2019 00:44, John Larkin wrote:

On Fri, 31 May 2019 16:26:01 -0700 (PDT), Klaus Kragelund
klauskvik@hotmail.com> wrote:

Why would you add that output decoupling capacitor when it is not needed?

To maybe avoid saturating the transformer. A good toroid has low DCR.
I could easily circulate a few amps DC in the primary.


None of the designs I have seen has a capacitor. Dig into it and find that you are chasing ghosts and just making a bad design by add a highly unlinear device

Notice that Class D is all about removing or compensating non linearities of the output stage.

Cheers

Klaus

If the transformer primary is center-tapped you could watch the tap
walking away from midpoint to trap imbalance but it seems a kind of
round-about way. Just another idea tossed into the cook-pot!

piglet

 

[Chris Jones]

On 01/06/2019 10:33, John Larkin wrote:

On Fri, 31 May 2019 17:15:14 -0700 (PDT), Lasse Langwadt Christensen
langwadt@fonz.dk> wrote:

lørdag den 1. juni 2019 kl. 01.55.43 UTC+2 skrev John Larkin:
On Fri, 31 May 2019 23:38:58 -0000 (UTC), Cursitor Doom
curd@notformail.com> wrote:

On Fri, 31 May 2019 15:36:39 -0700, John Larkin wrote:

I want to make a class-D audio amp, 150 watts or so, using a TI TPA3255
maybe. It's good for 600 watts mono!

Why class D? Doesn't seem like an obvious first choice for audio unless
it's for a PA system or something of that sort.

We plan to do three channels, 150 watts each, in a 2U rackmount
chassis.

It will simulate a 3-phase PM alternator hung on the gearbox of a jet
engine. We'll be able to program frequency, voltage, and complex
output impedance.


why do you need a transformer?

For isolation, to make 3-phase and other configurations, and to get
various output voltages.

Some of the downstream voltage regulators are weird. People like to
short out PM alternators for regulation. Our box will have to tolerate
that.


and why not some COTS amplifier, you can a 4 channel several 100watt amplifier in 2U for a few hundred $

We'll probably do our own class-D modules. We could use one of the TI
eval boards, but they are big and have a zillion jumpers and goofy
connectors.

We can get a 48V, 600 watt MeanWell power supply for $75!

We were thinking about putting the TPA3255 on the bottom of the board
and heat sinking it to the bottom of the box, which avoids a fan. It
has a huge, grounded power pad on the top of the chip.

Isn't most audio power class D now?

Have you seen these? The THD, IMD and noise specs are quite good:
https://www.hypex.nl/oem-audio-amplifiers/

 

[Jasen Betts]

On 2019-06-01, John Larkin <jjlarkin@highlandtechnology.com> wrote:

On Sat, 1 Jun 2019 00:42:45 -0700 (PDT), Phil Allison
pallison49@gmail.com> wrote:


We're selling a lab-grade voltage source, so we want the output to be
stiff.

An alternator is a current source, non-ideal due to the gap and
other physical constraints, but essentially it is a current source.
Jim T. explanind this here several years ago and it stuck with me.

After actualy thinking about how an alternator works, I could see that
it could only ever be a current source. consider what drive you'd
need if you were to replace the rotor with a sationary core and wanted
the same output waveforms.

I estimated the 20 mohms primary DCR by scaling from a smaller
toroid that we have. The AC output impedance is a separate issue from
the DC primary current hazard.

We will be sensing output current to control the complex output
impedance, so we can in theory tune the box Zout to zero by canceling
the transformer impedance. That approaches building an oscillator, but
we might take out some of the native impedance.

Why not start with a current source driving the primary of the
transformer and simulate extra the leakage inductance caused by the gap.

But alternators are very inductive, and our main goal is to simulate
alternators.

control current in the fast inner loop. control voltage in the slow
outer loop.


--
When I tried casting out nines I made a hash of it.

 

[John Larkin]

On Sun, 02 Jun 2019 10:32:53 +0300, upsidedown@downunder.com wrote:

On Sat, 01 Jun 2019 08:44:48 -0700, John Larkin
jjlarkin@highlandtechnology.com> wrote:


Or how about a high inductance but low resistance external solenoid
across toroid primary ? Apparently the frequency is in the 400 Hz
ballpark, so even less solenoid inductance should suffice, compared to
50/60 Hz.

I'm guessing that the TI amp would fight to maintain its output offset
voltage. A series cap would be a lot easier. I could quit bitching and
use some big caps. Probably don't need the diodes.

The output LC LFPs are outside of any feedback loops, so the LPF
filter inductor DC resistances are in series with the load DC
resistances, thus limiting the DC current.

Right, they add to the output DCR loop. I do want to keep them small,
ideally surface mount and low DCR. The TI chip in mono mode wants 4
inductors with pairs essentially in parallel. The 4 inductors might
add 10 mohms or so to the loop.




--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[John Larkin]

On Sun, 2 Jun 2019 12:51:45 -0000 (UTC), Jasen Betts
<jasen@xnet.co.nz> wrote:

On 2019-06-01, John Larkin <jjlarkin@highlandtechnology.com> wrote:
On Sat, 1 Jun 2019 00:42:45 -0700 (PDT), Phil Allison
pallison49@gmail.com> wrote:


We're selling a lab-grade voltage source, so we want the output to be
stiff.

An alternator is a current source, non-ideal due to the gap and
other physical constraints, but essentially it is a current source.
Jim T. explanind this here several years ago and it stuck with me.

After actualy thinking about how an alternator works, I could see that
it could only ever be a current source. consider what drive you'd
need if you were to replace the rotor with a sationary core and wanted
the same output waveforms.

I estimated the 20 mohms primary DCR by scaling from a smaller
toroid that we have. The AC output impedance is a separate issue from
the DC primary current hazard.

We will be sensing output current to control the complex output
impedance, so we can in theory tune the box Zout to zero by canceling
the transformer impedance. That approaches building an oscillator, but
we might take out some of the native impedance.

Why not start with a current source driving the primary of the
transformer and simulate extra the leakage inductance caused by the gap.

The class D amps are inherently low impedance out. We's drive each amp
from an FPGA and a DAC, to synthesize our sine waves. We'd sense final
(after the transformer) voltage and current, digitize, and stuff that
back into the FPGA. Then we can synthesize complex output impedance,
anything from a voltage source to an inductive current source.

Should be fun to Spice.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[John Larkin]

On Sat, 1 Jun 2019 19:16:39 -0700 (PDT), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:

sřndag den 2. juni 2019 kl. 04.05.06 UTC+2 skrev John Larkin:
On Sat, 1 Jun 2019 18:50:48 -0700 (PDT), tabbypurr@gmail.com wrote:

On Saturday, 1 June 2019 17:36:48 UTC+1, John Larkin wrote:

We're selling a lab-grade voltage source, so we want the output to be
stiff. I estimated the 20 mohms primary DCR by scaling from a smaller
toroid that we have. The AC output impedance is a separate issue from
the DC primary current hazard.

We will be sensing output current to control the complex output
impedance, so we can in theory tune the box Zout to zero by canceling
the transformer impedance. That approaches building an oscillator, but
we might take out some of the native impedance.

But alternators are very inductive, and our main goal is to simulate
alternators.

How do you intend to simulate the voltage spike when they suddenly reduce load?


NT

A bit of our simulated inductance will be a real inductor. It can do
the fast stuff, and our DSP loop can take over behind that.

It's similar to making a super-wideband inductor by making a series
string of little and big inductors. People do that in bias tees and
such.

The real-life load on the alternator will probably be shunt regulator,
bridge rectifier, capacitor, so really fast spikes probably wouldn't
matter much.

We're trying to get them to lend us an alternator. We could spin that
somehow and see how it behaves.


https://youtu.be/D4DqyElNFAs

I'm thinking we could just chuck it in one of our milling machines and
spin it up. That guy did an awful lot of machining. And talking.




--

John Larkin Highland Technology, Inc

lunatic fringe electronics