class-D amp so far...

[server]

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?



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[boB]

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.

At my last company, we made 3 kW 60 Hz inverters with 20 kHz switching
and large-ish 60 Hz transformers. Worked well as long as you keep the
high frequency switching off the transformer and core.

 

[piglet]

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

 

[boB]

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?

If it were my circuit and the user can load it anyway they want, I
would take that current monitor output and stop the show when either
polarity exceeds a predertimed value for overlod protection

 

[boB]

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.

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.

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

 

[server]

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.

The load is usually a switchmode shunt regulator followed by a 3-phase
bridge and a filter cap, the customer\'s FADEC.

At my last company, we made 3 kW 60 Hz inverters with 20 kHz switching
and large-ish 60 Hz transformers. Worked well as long as you keep the
high frequency switching off the transformer and core.

Laminated transformers are sorta tolerant of a little DC. This toroid
isn\'t. Caps with low ESR and high AC current handling are a major
issue here.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[server]

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.

Yeah, the big caps are a nuisance. Counting on a servo alone is
tempting but tricky. Too much risk maybe.

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

I\'ve seen mosfet substrate diodes do ugly things that weren\'t
simulated. I may as well add some diodes; they don\'t cost much.

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

piglet

Yes. The current sensor feeds back into the FPGA, and that lets us
program the effective source impedance that the user sees. That\'s
compatible with making this switcher open-loop. We\'ll add a bit of
real inductance too.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[server]

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!




--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[server]

On Fri, 06 Nov 2020 12:23:43 -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?


If it were my circuit and the user can load it anyway they want, I
would take that current monitor output and stop the show when either
polarity exceeds a predertimed value for overlod protection

The existing code has too many protections, so customer abuse is
shutting us down. One existing protection is too much current for too
much time, which we\'ll keep but really tone down. We need to tolerate
a huge overload for a few seconds maybe. We won\'t fry a transformer in
a few seconds.

The shunt current is used to program the effective impedance, so we
can control the short-circuit current.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[boB]

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.

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

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.

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.

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.

 

[Jeroen Belleman]

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

 

[server]

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?

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.

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.

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.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[boB]

On Fri, 06 Nov 2020 13:05:05 -0800, jlarkin@highlandsniptechnology.com
wrote:

On Fri, 06 Nov 2020 12:23:43 -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?


If it were my circuit and the user can load it anyway they want, I
would take that current monitor output and stop the show when either
polarity exceeds a predertimed value for overlod protection

The existing code has too many protections, so customer abuse is
shutting us down. One existing protection is too much current for too
much time, which we\'ll keep but really tone down. We need to tolerate
a huge overload for a few seconds maybe. We won\'t fry a transformer in
a few seconds.

Oh my ! No, the transformer is nothing to worry about burning up !

It\'s those FETs you have to worry about... Unless it\'s a really
shitty xformer. I doubt that is possible with your stuff. You know
what you\'re doing here.

The shunt current is used to program the effective impedance, so we
can control the short-circuit current.

 

[boB]

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.

 

[server]

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

I could locally demodulate the output of the delta-sigma ADC that
monitors the current shunt; that just takes a lowpass filter. But a
few big caps take less thinking.

A junky DC servo, on the differential bridge voltage, could protect
the caps. It would only need to be accurate to a volt maybe, which
would be easy.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[boB]

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.

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 ?

 

[server]

On Fri, 06 Nov 2020 14:38:35 -0800, boB <boB@K7IQ.com> wrote:

On Fri, 06 Nov 2020 13:05:05 -0800, jlarkin@highlandsniptechnology.com
wrote:

On Fri, 06 Nov 2020 12:23:43 -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?


If it were my circuit and the user can load it anyway they want, I
would take that current monitor output and stop the show when either
polarity exceeds a predertimed value for overlod protection

The existing code has too many protections, so customer abuse is
shutting us down. One existing protection is too much current for too
much time, which we\'ll keep but really tone down. We need to tolerate
a huge overload for a few seconds maybe. We won\'t fry a transformer in
a few seconds.


Oh my ! No, the transformer is nothing to worry about burning up !

I just tested one. It\'s about 4 deg C/watt on the bench in still air,
with maybe a 30 minute time constant. That\'s measuring actual copper
temperature. It could absorb all the power I have available, about a
kilowatt, for 30 seconds or so.

It\'s those FETs you have to worry about... Unless it\'s a really
shitty xformer. I doubt that is possible with your stuff. You know
what you\'re doing here.

I\'ll just use fets that can short out more current than the power
supply has. That\'s easy.





--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[server]

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.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[server]

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.




--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[boB]

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.