class-D amp so far...

[Phil Hobbs]

On 11/6/20 8:44 PM, jlarkin@highlandsniptechnology.com wrote:

On Fri, 06 Nov 2020 17:05:53 -0800, boB <boB@K7IQ.com> wrote:

On Fri, 06 Nov 2020 23:29:05 +0100, Jeroen Belleman
jeroen@nospam.please> wrote:

On 2020-11-06 21:45, jlarkin@highlandsniptechnology.com wrote:
On Fri, 06 Nov 2020 12:12:46 -0800, boB <boB@K7IQ.com> wrote:

On Fri, 06 Nov 2020 09:36:10 -0800, jlarkin@highlandsniptechnology.com
wrote:

The goal is a bulletproof 3-phase AC power source, maybe 250
watts/phase, but huge overload capacity for a few seconds. Here\'s my
amp concept for one phase:

https://www.dropbox.com/s/jijl78e026qjbgb/P902B_1.jpg?raw=1

https://www.dropbox.com/s/3rp94pxt2ou70qf/P902B_1.asc?dl=0


Two issues:

The DC blocking cap C4 will be huge, probably 2 or 3 in parallel, 6
volt lytics. They might tolerate a volt or so reverse DC. So I can
take my chances on offset, or servo the DC offset, or something.

The mosfets were just pulled from the LT Spice list. I\'ll have to find
some monster TO247s that can\'t be blown up. But I don\'t trust any
mosfet substrate diode model. Should I add schottky diodes across the
fets? Maybe two surface-mount SMB diodes per fet?


Looks pretty good. Why are you using a coupling capacitor again ? I
don\'t think you should need it ? At least from the primary side.
Maybe if a rectified load is connected it might be necessary ?
That\'s easy to simulate.

The toroidal transformer saturates with just a little DC voltage on
the primary. I don\'t know if I could trust a servo circuit to keep the
DC offset low enough.

You don\'t servo the DC voltage to zero, you servo the DC current!

Jeroen Belleman


Yep ! One begets the other !

But volt-seconds balance on the core is what matters.

This can also be a problem on push-pull supplies if the duty cycle
isn\'t 50%

There are different and fun kind of ways to fix this or keep it
centered where it belongs.

Myself, I would rather not have to use a series capacitor but it
probably doesn\'t matter too much as long as that ESR is really low and
doesn\'t get too reverse biased.



If I come off the two outputs, after the LC filters, I can go into a
diffamp and then an integrator. With 1% parts, I can probably keep the
offset below a volt or so. With 0.1% resistors, it would be
correspondingly better, a fraction of a volt. Still too much for the
transformer.

I tested some candidate 10mF 6.3 volt caps. At 1 or 1.5 volts reverse
bias, leakage current is low and declining, maybe 40 uA after a while.
At 2 volts, it\'s 200 uA and increasing. I think increasing is bad.

Posting about things like, and getting peoples opinions, helps me
think.

Kinda crazy, 5 or so giant caps to keep DC out of my transformer, and
a servo circuit to protect the caps.

Seems like you could use the servo to get rid of the DC, if you can
sense the right thing. How about a sort of Royerish idea--can you sense
the nonlinearity of the I(t) curve and make the average of the quadratic
term go away?

Cheers

Phil


Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[server]

On Sat, 7 Nov 2020 02:48:58 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 11/6/20 8:44 PM, jlarkin@highlandsniptechnology.com wrote:
On Fri, 06 Nov 2020 17:05:53 -0800, boB <boB@K7IQ.com> wrote:

On Fri, 06 Nov 2020 23:29:05 +0100, Jeroen Belleman
jeroen@nospam.please> wrote:

On 2020-11-06 21:45, jlarkin@highlandsniptechnology.com wrote:
On Fri, 06 Nov 2020 12:12:46 -0800, boB <boB@K7IQ.com> wrote:

On Fri, 06 Nov 2020 09:36:10 -0800, jlarkin@highlandsniptechnology.com
wrote:

The goal is a bulletproof 3-phase AC power source, maybe 250
watts/phase, but huge overload capacity for a few seconds. Here\'s my
amp concept for one phase:

https://www.dropbox.com/s/jijl78e026qjbgb/P902B_1.jpg?raw=1

https://www.dropbox.com/s/3rp94pxt2ou70qf/P902B_1.asc?dl=0


Two issues:

The DC blocking cap C4 will be huge, probably 2 or 3 in parallel, 6
volt lytics. They might tolerate a volt or so reverse DC. So I can
take my chances on offset, or servo the DC offset, or something.

The mosfets were just pulled from the LT Spice list. I\'ll have to find
some monster TO247s that can\'t be blown up. But I don\'t trust any
mosfet substrate diode model. Should I add schottky diodes across the
fets? Maybe two surface-mount SMB diodes per fet?


Looks pretty good. Why are you using a coupling capacitor again ? I
don\'t think you should need it ? At least from the primary side.
Maybe if a rectified load is connected it might be necessary ?
That\'s easy to simulate.

The toroidal transformer saturates with just a little DC voltage on
the primary. I don\'t know if I could trust a servo circuit to keep the
DC offset low enough.

You don\'t servo the DC voltage to zero, you servo the DC current!

Jeroen Belleman


Yep ! One begets the other !

But volt-seconds balance on the core is what matters.

This can also be a problem on push-pull supplies if the duty cycle
isn\'t 50%

There are different and fun kind of ways to fix this or keep it
centered where it belongs.

Myself, I would rather not have to use a series capacitor but it
probably doesn\'t matter too much as long as that ESR is really low and
doesn\'t get too reverse biased.



If I come off the two outputs, after the LC filters, I can go into a
diffamp and then an integrator. With 1% parts, I can probably keep the
offset below a volt or so. With 0.1% resistors, it would be
correspondingly better, a fraction of a volt. Still too much for the
transformer.

I tested some candidate 10mF 6.3 volt caps. At 1 or 1.5 volts reverse
bias, leakage current is low and declining, maybe 40 uA after a while.
At 2 volts, it\'s 200 uA and increasing. I think increasing is bad.

Posting about things like, and getting peoples opinions, helps me
think.

Kinda crazy, 5 or so giant caps to keep DC out of my transformer, and
a servo circuit to protect the caps.

Seems like you could use the servo to get rid of the DC, if you can
sense the right thing. How about a sort of Royerish idea--can you sense
the nonlinearity of the I(t) curve and make the average of the quadratic
term go away?

Cheers

Phil

Yikes!

Here\'s what I have so far. The servo seems to work enough to protect
the big caps, but this simulates at 11 hours per second, so it\'s a tad
hard to tune. The integrator could be slower.

It will also consume my hard drive with the .raw file if I let it run
very long.

https://www.dropbox.com/s/3phncj6yarx4qna/P902B_3.asc?dl=0

I can kick this off, go to Loews and Bevmo, take a nap, and then see
how it\'s doing.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[Phil Hobbs]

On 11/7/20 2:43 PM, jlarkin@highlandsniptechnology.com wrote:

On Sat, 7 Nov 2020 02:48:58 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 11/6/20 8:44 PM, jlarkin@highlandsniptechnology.com wrote:
On Fri, 06 Nov 2020 17:05:53 -0800, boB <boB@K7IQ.com> wrote:

On Fri, 06 Nov 2020 23:29:05 +0100, Jeroen Belleman
jeroen@nospam.please> wrote:

On 2020-11-06 21:45, jlarkin@highlandsniptechnology.com wrote:
On Fri, 06 Nov 2020 12:12:46 -0800, boB <boB@K7IQ.com> wrote:

On Fri, 06 Nov 2020 09:36:10 -0800, jlarkin@highlandsniptechnology.com
wrote:

The goal is a bulletproof 3-phase AC power source, maybe 250
watts/phase, but huge overload capacity for a few seconds. Here\'s my
amp concept for one phase:

https://www.dropbox.com/s/jijl78e026qjbgb/P902B_1.jpg?raw=1

https://www.dropbox.com/s/3rp94pxt2ou70qf/P902B_1.asc?dl=0


Two issues:

The DC blocking cap C4 will be huge, probably 2 or 3 in parallel, 6
volt lytics. They might tolerate a volt or so reverse DC. So I can
take my chances on offset, or servo the DC offset, or something.

The mosfets were just pulled from the LT Spice list. I\'ll have to find
some monster TO247s that can\'t be blown up. But I don\'t trust any
mosfet substrate diode model. Should I add schottky diodes across the
fets? Maybe two surface-mount SMB diodes per fet?


Looks pretty good. Why are you using a coupling capacitor again ? I
don\'t think you should need it ? At least from the primary side.
Maybe if a rectified load is connected it might be necessary ?
That\'s easy to simulate.

The toroidal transformer saturates with just a little DC voltage on
the primary. I don\'t know if I could trust a servo circuit to keep the
DC offset low enough.

You don\'t servo the DC voltage to zero, you servo the DC current!

Jeroen Belleman


Yep ! One begets the other !

But volt-seconds balance on the core is what matters.

This can also be a problem on push-pull supplies if the duty cycle
isn\'t 50%

There are different and fun kind of ways to fix this or keep it
centered where it belongs.

Myself, I would rather not have to use a series capacitor but it
probably doesn\'t matter too much as long as that ESR is really low and
doesn\'t get too reverse biased.



If I come off the two outputs, after the LC filters, I can go into a
diffamp and then an integrator. With 1% parts, I can probably keep the
offset below a volt or so. With 0.1% resistors, it would be
correspondingly better, a fraction of a volt. Still too much for the
transformer.

I tested some candidate 10mF 6.3 volt caps. At 1 or 1.5 volts reverse
bias, leakage current is low and declining, maybe 40 uA after a while.
At 2 volts, it\'s 200 uA and increasing. I think increasing is bad.

Posting about things like, and getting peoples opinions, helps me
think.

Kinda crazy, 5 or so giant caps to keep DC out of my transformer, and
a servo circuit to protect the caps.

Seems like you could use the servo to get rid of the DC, if you can
sense the right thing. How about a sort of Royerish idea--can you sense
the nonlinearity of the I(t) curve and make the average of the quadratic
term go away?

Cheers

Phil

Yikes!

I bet it could be done pretty well--if the nonlinearity is symmetrical,
you\'re in the middle of the B-H curve. If the core is starting to
saturate on one half-cycle, you\'ll have some curvature, and if you\'re
really getting into trouble, there\'ll be a big spike. A few-turn sense
winding would be the bee\'s knees, but you already have the transformers.

Of course, since you have rich customers, you don\'t have to sweat the
BOM cost that much--why not wire the caps up as a nonpolar? (It would
only take four times as many.)

Here\'s what I have so far. The servo seems to work enough to protect
the big caps, but this simulates at 11 hours per second, so it\'s a tad
hard to tune. The integrator could be slower.

It will also consume my hard drive with the .raw file if I let it run
very long.

https://www.dropbox.com/s/3phncj6yarx4qna/P902B_3.asc?dl=0

I can kick this off, go to Loews and Bevmo, take a nap, and then see
how it\'s doing.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[server]

There are many ways to measure the magnetization level of a transformer core.

https://www.researchgate.net/publication/224188430_Zeroing_Transformeraposs_DC_Current_in_Resonant_Converters_with_No_Series_Capacitors

https://www.semanticscholar.org/paper/A-detection-method-of-DC-magnetization-utilizing-of-Umetani-Itoh/648b057c36748b8d24669844a2caaf9626b26afa

Flux Balancing Control of Ungapped Nanocrystalline Core-Based Transformer in Dual Active Bridge Converters
https://ieeexplore.ieee.org/document/9056515

https://www.researchgate.net/publication/343277812_High_Precision_Wide_Bandwidth_DC_Current_Transducer_Based_on_the_Platise_Flux_Sensor

US patents
http://www.google.com/patents/US4709132
https://patents.google.com/patent/US1524285

https://www.pes-publications.ee.ethz.ch/uploads/tx_ethpublications/08_Flux_Balancing_of_Isolation_Ortiz_01.pdf
Fig. 4(d). Continuous measurement of core’s internal flux

\"Flux-Gate: The flux-gate principle is a well-known
concept for current measurement [14]. This measurement principle can be adapted in order to build a flux-density transducer,
as presented in [15] and shown in Fig. 4(d). In this concept,
an E-type core is utilized whereby the primary and secondary
windings are placed around the core’s middle leg while two additional windings are placed in one of the “I” parts of the core,
as depicted in Fig. 4(d). With this arrangement, a dc bias in the
flux-density would result in a change in the inductance in the
terminals of the auxiliary winding, thus enabling monitoring of
the flux density in the core.\"

With DC current bias this probe coil on E-core:
http://ixbt.photo/?id=photo:839539
yellow - magnetization current

use 2 toroidal cores:
http://archive.org/stream/radiotelephony00goldgoog#page/n124/mode/2up

 

[boB]

On Sun, 8 Nov 2020 02:24:39 -0800 (PST), plastcontrol.ru@gmail.com
wrote:

There are many ways to measure the magnetization level of a transformer core.

https://www.researchgate.net/publication/224188430_Zeroing_Transformeraposs_DC_Current_in_Resonant_Converters_with_No_Series_Capacitors

https://www.semanticscholar.org/paper/A-detection-method-of-DC-magnetization-utilizing-of-Umetani-Itoh/648b057c36748b8d24669844a2caaf9626b26afa

Flux Balancing Control of Ungapped Nanocrystalline Core-Based Transformer in Dual Active Bridge Converters
https://ieeexplore.ieee.org/document/9056515

https://www.researchgate.net/publication/343277812_High_Precision_Wide_Bandwidth_DC_Current_Transducer_Based_on_the_Platise_Flux_Sensor

US patents
http://www.google.com/patents/US4709132
https://patents.google.com/patent/US1524285

https://www.pes-publications.ee.ethz.ch/uploads/tx_ethpublications/08_Flux_Balancing_of_Isolation_Ortiz_01.pdf
Fig. 4(d). Continuous measurement of core’s internal flux

\"Flux-Gate: The flux-gate principle is a well-known
concept for current measurement [14]. This measurement principle can be adapted in order to build a flux-density transducer,
as presented in [15] and shown in Fig. 4(d). In this concept,
an E-type core is utilized whereby the primary and secondary
windings are placed around the core’s middle leg while two additional windings are placed in one of the “I” parts of the core,
as depicted in Fig. 4(d). With this arrangement, a dc bias in the
flux-density would result in a change in the inductance in the
terminals of the auxiliary winding, thus enabling monitoring of
the flux density in the core.\"

With DC current bias this probe coil on E-core:
http://ixbt.photo/?id=photo:839539
yellow - magnetization current

use 2 toroidal cores:
http://archive.org/stream/radiotelephony00goldgoog#page/n124/mode/2up

Some nice links !

I really like the Google OCR old books on archive.org as well.

Great histories !

 

[server]

The DC blocking capacitor only creates the illusion of correct operation of the transformer.
Сapacitor causes transient problems.
A circuit with a capacitor in the primary coil will fail if the secondary is loaded an incandescent lamp with a diode.

 

[Rocky]

On Monday, 09 November 2020 at 11:24:46 UTC+2, plastco...@gmail.com wrote:

The DC blocking capacitor only creates the illusion of correct operation of the transformer.
Сapacitor causes transient problems.
A circuit with a capacitor in the primary coil will fail if the secondary is loaded an incandescent lamp with a diode.

Also, the cap and transformer form a series resonant circuit that may give unexpected issues.

 

[server]

On Mon, 9 Nov 2020 01:24:39 -0800 (PST), plastcontrol.ru@gmail.com
wrote:

>The DC blocking capacitor only creates the illusion of correct operation of the transformer.

I can sell that.

>?apacitor causes transient problems.

How? It simulates nicely, and the rev A board works... just not enough
brute power. We will need to parallel enough caps to manage the ripple
current.

>A circuit with a capacitor in the primary coil will fail if the secondary is loaded an incandescent lamp with a diode.

I don\'t plan to do that; the load is symmetric three-phase. But if an
asymmetric load did saturate the transformer, my brute-force dumb amp
will just power through.

I\'m simulating now, with a .step on the sine wave frequency. Time for
a nap or a hike or something while that runs.

Mike quit Analog and has hinted at a next-gen simulator after LT
Spice. I think it ought to use an Nvidia card to get us, say, 1000x
the speed of running on a PC.

I want part value sliders and I want to see waveforms change
instantly.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[John Larkin]

On Fri, 06 Nov 2020 18:48:12 -0800, boB <boB@K7IQ.com> wrote:

On Fri, 06 Nov 2020 17:51:34 -0800, jlarkin@highlandsniptechnology.com
wrote:

On Fri, 06 Nov 2020 17:16:45 -0800, boB <boB@K7IQ.com> wrote:

On Fri, 06 Nov 2020 14:37:00 -0800, jlarkin@highlandsniptechnology.com
wrote:

On Fri, 06 Nov 2020 13:33:06 -0800, boB <boB@K7IQ.com> wrote:

On Fri, 06 Nov 2020 12:58:30 -0800, jlarkin@highlandsniptechnology.com
wrote:

On Fri, 06 Nov 2020 12:36:31 -0800, boB <boB@K7IQ.com> wrote:

On Fri, 6 Nov 2020 20:19:37 +0000, piglet <erichpwagner@hotmail.com
wrote:

On 06/11/2020 5:36 pm, jlarkin@highlandsniptechnology.com wrote:
The goal is a bulletproof 3-phase AC power source, maybe 250
watts/phase, but huge overload capacity for a few seconds. Here\'s my
amp concept for one phase:

https://www.dropbox.com/s/jijl78e026qjbgb/P902B_1.jpg?raw=1

https://www.dropbox.com/s/3rp94pxt2ou70qf/P902B_1.asc?dl=0


Two issues:

The DC blocking cap C4 will be huge, probably 2 or 3 in parallel, 6
volt lytics. They might tolerate a volt or so reverse DC. So I can
take my chances on offset, or servo the DC offset, or something.

The mosfets were just pulled from the LT Spice list. I\'ll have to find
some monster TO247s that can\'t be blown up. But I don\'t trust any
mosfet substrate diode model. Should I add schottky diodes across the
fets? Maybe two surface-mount SMB diodes per fet?




C4 might help limit damage propagation if the mosfets die but a slow dc
offset removal servo will cost less on the BOM.

I usually add didoes across fets in spice for simulation purposes even
though in real life I\'d likely rely on the body diode.

Are you going to add simulated source inductance and resistance like you
did on the previous model - can that be done without feedback?

piglet



Also, is the 48V being supplied by a battery ? IF so, I would
definitely add overcurrent protection. Battery current is what kills
things.

It\'s a 1000 watt MeanWell power supply. It current limits at some
value that I need to measure. Wild guess 30 amps maybe.


And if either battery supply or not, does the output voltage need to
be regulated ? Are you really going to use the LTC4444 controllers or
are you using a micro ? A micro can do all the logic with added half
bridge drivers as well as output voltage regulation feedback using a
differential op-amp ciruit into its A/D converter. Overcurrent can be
done that way too using a pin from your current monitor and comparator
or even A/D converter input if it\'s fast enough.

The existing board is analog in, analog out, and this is a
higher-power drop-in. The shunt feeds an isolated delta-sigma ADC that
goes back into our FPGA on the main board, so we know the current.


But then again, maybe this is all overkill. I like desaturation
protection drivers.


I want these fets to never come out of saturation!

Ahhh... So much more of a reason to use desaturation protection.

Wouldn\'t that turn them off? What else could it do?


Yeah, that\'s what it would do. It can turn off cycle by cycle (HF
cycles) if you want it to though. Might or might not be noticeable
depending on how often it trips. This protection also has an isolated
feedback so your FPGA or micro can handle things smartly. For
example, you could count the number of trips and if too many happen in
a certain amount of time, shut off or reduce amplitude.

We\'re doing all that, and when the customer does a certain thing, we
shut down. I want to apply a huge amount of brute power to get over
his surge. Maybe 10 seconds would do.






Right now, I like the Rohm FET driver I think. Easy to use and fairly
cheap as far as drivers with desat protection go. And 4 amps I think
it is. You would need 4 of them. BM6104FV-C

The advantage of the LTC4444 is the LT Spice model. That\'s why we pay
extra for LTC parts.



And this is exaxtly why LTspice is free and a great tool.



We adjust this limit to something higher than our highest allowed
surge current so that it can also help with simple over-current.
Also as the FET gets hotter and its RdsOn rises, it will be more
sensetive.

A big enough fet would just stay on, and the big power supply could
current limit.


Yes, that certainly works too as long as the supply side capacitors
can\'t supply too much blow-up-energy in addition.




For low ESR electrolytics, we like either UCC or Jianghai
http://www.jianghai-america.com/

Jianghai used to make a lot of the Panasonic capcitors in China which
were the best for low ESR. Unfortunately, there are tariffs for any
of these good caps right now. We\'ll see if those go away but I kind
of doubt it because even the democrats like all these taxes I\'m pretty
sure.

Reasonably sized radial caps seem to top out around 4 amps or so. I
could parallel four or five. We have lots of air flow, which would
help. The current limit is probably thermal.


I suppose you already have a toiroid or transformer picked out. A
lower permeability toroid would be more lenient on DC offset.
A servo works too but current limit is good for double added
protection.

Getting the custom transformers was a nuisance, and we have a lot of
them now.


Yep. Totally understan that !


BTW, this would be bidirectional from output back to the power
supply.... Are the loads all going to be resistive ?


The load is a shorting shunt regulator, namely 3 diodes and 3 mosfets
that feed an output cap. A really dumb regulator PWMs the fets as
needed to sort of regulate the DC. Fets off, it\'s a 6-diode bridge.
Fets on, it\'s a short.

It\'s usually driven by a PM alternator, which doesn\'t mind being
shorted.


Ya know.... You can also combine those two separate output inductors
(L3, L6) onto one core and use less turns. Then you would also only
have to use one, instead of two C\'s (C6, C8) across, going to the
transformer since it\'s all isolated from there.

They are stock Coilcraft parts now; anything else would probably have
to be custom. One of my guys is doing a test to see how hard we can
overload them for 15 seconds, and how air flow affects theta. Putting
more wire on one core might be thermally disadvantageous.

The caps are small and cheap. I should make sure they won\'t fry from
ESR heating, but they only see the switcher ripple current, which
isn\'t huge. I could use four.

 

[server]

On Fri, 06 Nov 2020 09:36:10 -0800, jlarkin@highlandsniptechnology.com
wrote:

The goal is a bulletproof 3-phase AC power source, maybe 250
watts/phase, but huge overload capacity for a few seconds. Here\'s my
amp concept for one phase:

https://www.dropbox.com/s/jijl78e026qjbgb/P902B_1.jpg?raw=1

https://www.dropbox.com/s/3rp94pxt2ou70qf/P902B_1.asc?dl=0


Two issues:

The DC blocking cap C4 will be huge, probably 2 or 3 in parallel, 6
volt lytics. They might tolerate a volt or so reverse DC. So I can
take my chances on offset, or servo the DC offset, or something.

The mosfets were just pulled from the LT Spice list. I\'ll have to find
some monster TO247s that can\'t be blown up. But I don\'t trust any
mosfet substrate diode model. Should I add schottky diodes across the
fets? Maybe two surface-mount SMB diodes per fet?

Given that I want my amp to output maximum possible power for 10
seconds or so, I probably want fets with low Rds-on, like 10 milliohms
maybe, to reduce I2R power at the expense of capacitive switching
losses, which won\'t increase with power.

More interestingly, I want my heat sinks to have maximum mass, without
much regard for the classic degsC/watt spec. Air flow won\'t matter
much in 10 seconds. So a heat sink should be a solid block of
aluminum. Fins just waste the opportunity for mass.

Annoyingly, the people who sell heat sinks don\'t know much about this
stuff, so seldom list the weight of their parts. And they are slow to
answer questions, as in days so far. I\'ll have to get some and weigh
them.

Conveniently, 1 watt dumped into 1 gram of aluminum rises about 1 degc
per second. The electrical analogy is 1 farad, so simple circuit
theory or Spice can do my thermal transient modeling.

Similarly, I care about the thermal mass of caps and inductors, not
their usual ratings.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[server]

On Tue, 10 Nov 2020 05:53:01 -0800, jlarkin@highlandsniptechnology.com
wrote:

On Fri, 06 Nov 2020 09:36:10 -0800, jlarkin@highlandsniptechnology.com
wrote:

The goal is a bulletproof 3-phase AC power source, maybe 250
watts/phase, but huge overload capacity for a few seconds. Here\'s my
amp concept for one phase:

https://www.dropbox.com/s/jijl78e026qjbgb/P902B_1.jpg?raw=1

https://www.dropbox.com/s/3rp94pxt2ou70qf/P902B_1.asc?dl=0


Two issues:

The DC blocking cap C4 will be huge, probably 2 or 3 in parallel, 6
volt lytics. They might tolerate a volt or so reverse DC. So I can
take my chances on offset, or servo the DC offset, or something.

The mosfets were just pulled from the LT Spice list. I\'ll have to find
some monster TO247s that can\'t be blown up. But I don\'t trust any
mosfet substrate diode model. Should I add schottky diodes across the
fets? Maybe two surface-mount SMB diodes per fet?

Given that I want my amp to output maximum possible power for 10
seconds or so, I probably want fets with low Rds-on, like 10 milliohms
maybe, to reduce I2R power at the expense of capacitive switching
losses, which won\'t increase with power.

More interestingly, I want my heat sinks to have maximum mass, without
much regard for the classic degsC/watt spec. Air flow won\'t matter
much in 10 seconds. So a heat sink should be a solid block of
aluminum. Fins just waste the opportunity for mass.

Annoyingly, the people who sell heat sinks don\'t know much about this
stuff, so seldom list the weight of their parts. And they are slow to
answer questions, as in days so far. I\'ll have to get some and weigh
them.

Conveniently, 1 watt dumped into 1 gram of aluminum rises about 1 degc
per second. The electrical analogy is 1 farad, so simple circuit
theory or Spice can do my thermal transient modeling.

Copper has similar specific heat capacity as aluminum, but due to the
higher density, the copper slab dimensions can be much smaller. In
addition, the heat conductivity is much better, so the heat spreads
quickly through the slab.

Attach a normal (aluminum) heatsink to the copper slab to remove the
_average_ heat power to the environment.

Similarly, I care about the thermal mass of caps and inductors, not
their usual ratings.

 

[Lasse Langwadt Christensen]

tirsdag den 10. november 2020 kl. 14.53.13 UTC+1 skrev jla...@highlandsniptechnology.com:

On Fri, 06 Nov 2020 09:36:10 -0800, jlarkin@highlandsniptechnology.com
wrote:

The goal is a bulletproof 3-phase AC power source, maybe 250
watts/phase, but huge overload capacity for a few seconds. Here\'s my
amp concept for one phase:

https://www.dropbox.com/s/jijl78e026qjbgb/P902B_1.jpg?raw=1

https://www.dropbox.com/s/3rp94pxt2ou70qf/P902B_1.asc?dl=0


Two issues:

The DC blocking cap C4 will be huge, probably 2 or 3 in parallel, 6
volt lytics. They might tolerate a volt or so reverse DC. So I can
take my chances on offset, or servo the DC offset, or something.

The mosfets were just pulled from the LT Spice list. I\'ll have to find
some monster TO247s that can\'t be blown up. But I don\'t trust any
mosfet substrate diode model. Should I add schottky diodes across the
fets? Maybe two surface-mount SMB diodes per fet?

Given that I want my amp to output maximum possible power for 10
seconds or so, I probably want fets with low Rds-on, like 10 milliohms
maybe, to reduce I2R power at the expense of capacitive switching
losses, which won\'t increase with power.

More interestingly, I want my heat sinks to have maximum mass, without
much regard for the classic degsC/watt spec. Air flow won\'t matter
much in 10 seconds. So a heat sink should be a solid block of
aluminum. Fins just waste the opportunity for mass.

Annoyingly, the people who sell heat sinks don\'t know much about this
stuff, so seldom list the weight of their parts. And they are slow to
answer questions, as in days so far. I\'ll have to get some and weigh
them.

just order aluminium bar or plate from a metal supply?

 

[server]

On Tue, 10 Nov 2020 07:38:48 -0800 (PST), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:

tirsdag den 10. november 2020 kl. 14.53.13 UTC+1 skrev jla...@highlandsniptechnology.com:
On Fri, 06 Nov 2020 09:36:10 -0800, jlarkin@highlandsniptechnology.com
wrote:

The goal is a bulletproof 3-phase AC power source, maybe 250
watts/phase, but huge overload capacity for a few seconds. Here\'s my
amp concept for one phase:

https://www.dropbox.com/s/jijl78e026qjbgb/P902B_1.jpg?raw=1

https://www.dropbox.com/s/3rp94pxt2ou70qf/P902B_1.asc?dl=0


Two issues:

The DC blocking cap C4 will be huge, probably 2 or 3 in parallel, 6
volt lytics. They might tolerate a volt or so reverse DC. So I can
take my chances on offset, or servo the DC offset, or something.

The mosfets were just pulled from the LT Spice list. I\'ll have to find
some monster TO247s that can\'t be blown up. But I don\'t trust any
mosfet substrate diode model. Should I add schottky diodes across the
fets? Maybe two surface-mount SMB diodes per fet?

Given that I want my amp to output maximum possible power for 10
seconds or so, I probably want fets with low Rds-on, like 10 milliohms
maybe, to reduce I2R power at the expense of capacitive switching
losses, which won\'t increase with power.

More interestingly, I want my heat sinks to have maximum mass, without
much regard for the classic degsC/watt spec. Air flow won\'t matter
much in 10 seconds. So a heat sink should be a solid block of
aluminum. Fins just waste the opportunity for mass.

Annoyingly, the people who sell heat sinks don\'t know much about this
stuff, so seldom list the weight of their parts. And they are slow to
answer questions, as in days so far. I\'ll have to get some and weigh
them.

just order aluminium bar or plate from a metal supply?

This would be easy, for two TO247 fets:

https://www.dropbox.com/s/imptbya809v8y4t/Aavid_Stack.jpg?raw=1

It\'s an Aavid heat sink and two aluminum nitride insulators, parts
that we have in stock. I need to do the measurements and math on all
that. I don\'t think that four of those heat sinks would fit on my
board, but maybe.

If it\'s borderline, I could lay out the board so that we could
substitute a big machined aluminum block if we had to.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[Lasse Langwadt Christensen]

tirsdag den 10. november 2020 kl. 17.11.31 UTC+1 skrev jla...@highlandsniptechnology.com:

On Tue, 10 Nov 2020 07:38:48 -0800 (PST), Lasse Langwadt Christensen
langwadt@fonz.dk> wrote:

tirsdag den 10. november 2020 kl. 14.53.13 UTC+1 skrev jla...@highlandsniptechnology.com:
On Fri, 06 Nov 2020 09:36:10 -0800, jlarkin@highlandsniptechnology.com
wrote:

The goal is a bulletproof 3-phase AC power source, maybe 250
watts/phase, but huge overload capacity for a few seconds. Here\'s my
amp concept for one phase:

https://www.dropbox.com/s/jijl78e026qjbgb/P902B_1.jpg?raw=1

https://www.dropbox.com/s/3rp94pxt2ou70qf/P902B_1.asc?dl=0


Two issues:

The DC blocking cap C4 will be huge, probably 2 or 3 in parallel, 6
volt lytics. They might tolerate a volt or so reverse DC. So I can
take my chances on offset, or servo the DC offset, or something.

The mosfets were just pulled from the LT Spice list. I\'ll have to find
some monster TO247s that can\'t be blown up. But I don\'t trust any
mosfet substrate diode model. Should I add schottky diodes across the
fets? Maybe two surface-mount SMB diodes per fet?

Given that I want my amp to output maximum possible power for 10
seconds or so, I probably want fets with low Rds-on, like 10 milliohms
maybe, to reduce I2R power at the expense of capacitive switching
losses, which won\'t increase with power.

More interestingly, I want my heat sinks to have maximum mass, without
much regard for the classic degsC/watt spec. Air flow won\'t matter
much in 10 seconds. So a heat sink should be a solid block of
aluminum. Fins just waste the opportunity for mass.

Annoyingly, the people who sell heat sinks don\'t know much about this
stuff, so seldom list the weight of their parts. And they are slow to
answer questions, as in days so far. I\'ll have to get some and weigh
them.

just order aluminium bar or plate from a metal supply?


This would be easy, for two TO247 fets:

https://www.dropbox.com/s/imptbya809v8y4t/Aavid_Stack.jpg?raw=1

It\'s an Aavid heat sink and two aluminum nitride insulators, parts
that we have in stock. I need to do the measurements and math on all
that. I don\'t think that four of those heat sinks would fit on my
board, but maybe.

If it\'s borderline, I could lay out the board so that we could
substitute a big machined aluminum block if we had to.

an aluminium bar in between the fets can screw a heat sink on top if needed

sorta like this: https://www.infineon.com/export/sites/default/media/products/irf/iraudamp7s.png_1360273644.png

 

[server]

On Tue, 10 Nov 2020 08:47:04 -0800 (PST), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:

tirsdag den 10. november 2020 kl. 17.11.31 UTC+1 skrev jla...@highlandsniptechnology.com:
On Tue, 10 Nov 2020 07:38:48 -0800 (PST), Lasse Langwadt Christensen
langwadt@fonz.dk> wrote:

tirsdag den 10. november 2020 kl. 14.53.13 UTC+1 skrev jla...@highlandsniptechnology.com:
On Fri, 06 Nov 2020 09:36:10 -0800, jlarkin@highlandsniptechnology.com
wrote:

The goal is a bulletproof 3-phase AC power source, maybe 250
watts/phase, but huge overload capacity for a few seconds. Here\'s my
amp concept for one phase:

https://www.dropbox.com/s/jijl78e026qjbgb/P902B_1.jpg?raw=1

https://www.dropbox.com/s/3rp94pxt2ou70qf/P902B_1.asc?dl=0


Two issues:

The DC blocking cap C4 will be huge, probably 2 or 3 in parallel, 6
volt lytics. They might tolerate a volt or so reverse DC. So I can
take my chances on offset, or servo the DC offset, or something.

The mosfets were just pulled from the LT Spice list. I\'ll have to find
some monster TO247s that can\'t be blown up. But I don\'t trust any
mosfet substrate diode model. Should I add schottky diodes across the
fets? Maybe two surface-mount SMB diodes per fet?

Given that I want my amp to output maximum possible power for 10
seconds or so, I probably want fets with low Rds-on, like 10 milliohms
maybe, to reduce I2R power at the expense of capacitive switching
losses, which won\'t increase with power.

More interestingly, I want my heat sinks to have maximum mass, without
much regard for the classic degsC/watt spec. Air flow won\'t matter
much in 10 seconds. So a heat sink should be a solid block of
aluminum. Fins just waste the opportunity for mass.

Annoyingly, the people who sell heat sinks don\'t know much about this
stuff, so seldom list the weight of their parts. And they are slow to
answer questions, as in days so far. I\'ll have to get some and weigh
them.

just order aluminium bar or plate from a metal supply?


This would be easy, for two TO247 fets:

https://www.dropbox.com/s/imptbya809v8y4t/Aavid_Stack.jpg?raw=1

It\'s an Aavid heat sink and two aluminum nitride insulators, parts
that we have in stock. I need to do the measurements and math on all
that. I don\'t think that four of those heat sinks would fit on my
board, but maybe.

If it\'s borderline, I could lay out the board so that we could
substitute a big machined aluminum block if we had to.


an aluminium bar in between the fets can screw a heat sink on top if needed

sorta like this: https://www.infineon.com/export/sites/default/media/products/irf/iraudamp7s.png_1360273644.png

We could tap the top of my heat sink and bolt a block there. I have
the height.

Maybe I have enough mass to get over my surge. Gotta weigh a heat
sink.

The Aavid sales rep contacted me. Useless. He doesn\'t even know what
he sells. Their part numbers are 96 digits long and the data sheets
are horrible.





--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[John Larkin]

On Tue, 10 Nov 2020 09:26:08 -0800, jlarkin@highlandsniptechnology.com
wrote:

On Tue, 10 Nov 2020 08:47:04 -0800 (PST), Lasse Langwadt Christensen
langwadt@fonz.dk> wrote:

tirsdag den 10. november 2020 kl. 17.11.31 UTC+1 skrev jla...@highlandsniptechnology.com:
On Tue, 10 Nov 2020 07:38:48 -0800 (PST), Lasse Langwadt Christensen
langwadt@fonz.dk> wrote:

tirsdag den 10. november 2020 kl. 14.53.13 UTC+1 skrev jla...@highlandsniptechnology.com:
On Fri, 06 Nov 2020 09:36:10 -0800, jlarkin@highlandsniptechnology.com
wrote:

The goal is a bulletproof 3-phase AC power source, maybe 250
watts/phase, but huge overload capacity for a few seconds. Here\'s my
amp concept for one phase:

https://www.dropbox.com/s/jijl78e026qjbgb/P902B_1.jpg?raw=1

https://www.dropbox.com/s/3rp94pxt2ou70qf/P902B_1.asc?dl=0


Two issues:

The DC blocking cap C4 will be huge, probably 2 or 3 in parallel, 6
volt lytics. They might tolerate a volt or so reverse DC. So I can
take my chances on offset, or servo the DC offset, or something.

The mosfets were just pulled from the LT Spice list. I\'ll have to find
some monster TO247s that can\'t be blown up. But I don\'t trust any
mosfet substrate diode model. Should I add schottky diodes across the
fets? Maybe two surface-mount SMB diodes per fet?

Given that I want my amp to output maximum possible power for 10
seconds or so, I probably want fets with low Rds-on, like 10 milliohms
maybe, to reduce I2R power at the expense of capacitive switching
losses, which won\'t increase with power.

More interestingly, I want my heat sinks to have maximum mass, without
much regard for the classic degsC/watt spec. Air flow won\'t matter
much in 10 seconds. So a heat sink should be a solid block of
aluminum. Fins just waste the opportunity for mass.

Annoyingly, the people who sell heat sinks don\'t know much about this
stuff, so seldom list the weight of their parts. And they are slow to
answer questions, as in days so far. I\'ll have to get some and weigh
them.

just order aluminium bar or plate from a metal supply?


This would be easy, for two TO247 fets:

https://www.dropbox.com/s/imptbya809v8y4t/Aavid_Stack.jpg?raw=1

It\'s an Aavid heat sink and two aluminum nitride insulators, parts
that we have in stock. I need to do the measurements and math on all
that. I don\'t think that four of those heat sinks would fit on my
board, but maybe.

If it\'s borderline, I could lay out the board so that we could
substitute a big machined aluminum block if we had to.


an aluminium bar in between the fets can screw a heat sink on top if needed

sorta like this: https://www.infineon.com/export/sites/default/media/products/irf/iraudamp7s.png_1360273644.png


We could tap the top of my heat sink and bolt a block there. I have
the height.

Maybe I have enough mass to get over my surge. Gotta weigh a heat
sink.

The Aavid sales rep contacted me. Useless. He doesn\'t even know what
he sells. Their part numbers are 96 digits long and the data sheets
are horrible.

I can use four of the little ones, same net thermal mass.

https://www.dropbox.com/s/8974x25unsgo1xq/Two_Sinks.jpg?raw=1

and they are not made by Aavid!

16 grams is plenty, and I don\'t need insulators.

 

[server]

On Fri, 06 Nov 2020 09:36:10 -0800, jlarkin@highlandsniptechnology.com
wrote:

The goal is a bulletproof 3-phase AC power source, maybe 250
watts/phase, but huge overload capacity for a few seconds. Here\'s my
amp concept for one phase:

https://www.dropbox.com/s/jijl78e026qjbgb/P902B_1.jpg?raw=1

https://www.dropbox.com/s/3rp94pxt2ou70qf/P902B_1.asc?dl=0


Two issues:

The DC blocking cap C4 will be huge, probably 2 or 3 in parallel, 6
volt lytics. They might tolerate a volt or so reverse DC. So I can
take my chances on offset, or servo the DC offset, or something.

The mosfets were just pulled from the LT Spice list. I\'ll have to find
some monster TO247s that can\'t be blown up. But I don\'t trust any
mosfet substrate diode model. Should I add schottky diodes across the
fets? Maybe two surface-mount SMB diodes per fet?

It\'s looking like this:

https://www.dropbox.com/s/4ffuu2chz23ys4o/P902B_pcb3.jpg?raw=1

The big fets (on 4 heat sinks, 16 grams each) and two big toroidal
inductors are on the bottom. There\'s a fan on the bottom too, blowing
right onto those parts.

All my available layout people are busy, so I\'m doing this myself.
There is a huge advantage to having the circuit in your head when you
do a layout.

Funny how, if you push stuff around aimlessly for a while, the pattern
sort of snaps itself into place. Of course, I have to option to change
the circuit, and they don\'t. Two of the big inductors don\'t want to
fit, so they are gone. I\'ll just blow a lot of air on the survivors.






--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard