Need the topology for a current to current SMPS, not voltage tovoltage SMPS

[John S]

lt-spice crashed before I coiuld save it.

when I had it start with the switch open it'd put 15GV on the
capacitor

That's probably because your input is a current source and you waited
too long to close the switch.

 

[Joerg]

[...]

Oops, I probably mixed you up with someone else. I thought it was stage
electronics for rock bands and stuff.

That was the last job. ;-) I've done a few career changes in the
last 10 years. Before that, one employer, oneish (perhaps two)
markets, but very different jobs every five to eight years.

5-8 years would be a bit much for me.

You have a very small view of the automotive market. That is for
sure.

I see it from two view points. One is the actual product and that often
doesn't look very good, both from a quality point of view and sometimes
also from an engineering point of view (flickering LED backlights
anyone?). Then from a people perspective and here talking to folks who
actually work in that field helps. Pretty much all of them reported
extreme pressure to keep NRE and R&D schedules down, which explains a
lot of the quality issues. To the point I wouldn't want to work there.
As a consultant maybe but niot if they'd demansd unrealistic timelines
like they often do from their employees.

There are automotive electronics that work quite well, mostly in
Japanese cars. In the end it boils down to the reliability ratings of
the various entities in the know.

ECUs have changed more than a little in 30 years. They will change
drastically, again, over the next ten. ...

Sure, incremental change. Same in medical ultrasound which is my home
turf. But ... after we built a flagship product in the late 80's and the
satellite R&D location was closed afterwards I wasn't too unhappy that I
could jump into consulting for the first time, and do something else.

... Hell, you'd have a hard time
showing up for work with your pants on, after being a consultant that
long. ;-)

As a consultant I get to wear shorts all summer long. When a web
conference with bigshots is coming up I have a "dress shirt on duty"
hanging in the lab closet

 

[George Herold]

Thanks, George. It believe this is a standard buck switcher without the

output filter capacitor.

Hi John, Here's the current to current buck that I drew... from upstream
https://www.dropbox.com/s/h2a8dyz0vzoovev/DSCF0031.JPG
I guess I could try simulating these, if I ever get 'free' time.

George H.

 

[John S]

Alas, the compliance current is around 50mA with a compliance voltage as
high as 1kV, which is destructive. A 'straight' shunt regulator either
shorts out the incoming 50 mA or let's it pass thru, but in this case I
sometimes need 800mA at a small 5Vdc. So, need some 'multiplication' of
the current - a capacitor. There is sufficient power if the system
operates with the compliance at around 80V at 50mA just have to somehow
convert that to 5Vdc at 800mA. But, in this case it will be super
necessary to monitor compliance voltage so it won't EVER go above 100V
in order to NOT kill parts. In this supply that protection circuit, or
'voltage limit', is the corollary of the standard 'current limit' in a
voltage supply!

So far it appears a variation of George Herold's approach may get me
there. the current charges a cap, which then supplies large amount of
power. Aain, corollary, using cap instead of inductor for the energy
storage/conversion.

Hi, Robert -

The thread has grown more to than I can re-read to capture all your
requirements. However, here are my thoughts...

Max allowed input voltage: 100V
Input current capability: 50mA
Output voltage required: 5V
Output current required: .8A

Rather than thinking about this as a current-to-current topology, think
about how much power you can put into the topology within your
constraints. You can't get more power out than your input capability and
limits. But, you know that.

A normal buck switching topology will provide all this. One thing to
note is that you cannot get more than 5W out if your max input voltage
is limited to 100V and your (constant) current is .05A. So, you can
forget the 10W requirement because of your 100V limit.

It seems to me that, using the standard buck topology, you will need to
adjust your control loop (and thinking) as follows:

-Never let the input voltage get above 100V. As it approaches that
limit, increase the duty cycle. This is equivalent to current limit.
After all, if you are able to reduce the voltage while the current
remains the same, input and output power is reduced. Note that this
requires some kind of load just as in a current transformer.

-If the load is reduced, the voltage will tend to rise. Increase the
duty cycle even more to hold the voltage. By increasing the duty cycle
to a much higher value, you will cause the input voltage to plummet
which will reduce the available input power.

What is your maximum load resistance?

-If it can be open or very high, then you need to provide another device
at the input, perhaps a depletion FET capabale of about 100mA at a few
hundred volts to stop things when the duty cycle is commanded to be at
100% or a bit less.

Just some thoughts. I apologize if I have stepped on any toes.

 

[John S]

Hi John, Here's the current to current buck that I drew... from upstream
https://www.dropbox.com/s/h2a8dyz0vzoovev/DSCF0031.JPG
I guess I could try simulating these, if I ever get 'free' time.

George H.

Yes, thank you, George. I saw it. But your image and your ASCII drawing
above do not agree. Your ASCII drawing is a standard buck without an
output filter capacitor. I agree with your ASCII (with, possibly, the
requirement for an output filter capacitor) for a scheme which could work.

 

[RobertMacy]

Hi, Robert -

The thread has grown more to than I can re-read to capture all your
requirements. However, here are my thoughts...

Max allowed input voltage: 100V
Input current capability: 50mA
Output voltage required: 5V
Output current required: .8A
....snip...loss of extra thoughts due to using AIOE that won't let me
quote more than ?? number of lines...
-If it can be open or very high, then you need to provide another device
at the input, perhaps a depletion FET capabale of about 100mA at a few
hundred volts to stop things when the duty cycle is commanded to be at
100% or a bit less.

Just some thoughts. I apologize if I have stepped on any toes.

You've got the gist of the problem. I made up some of the numbers and
didn't notice they didn't quite correlate. But you see the premise for the
problem.

To maintain some semblance of efficiency, I can't simply 'shunt' unused
power off.

 

[George Herold]

Yes, thank you, George. I saw it. But your image and your ASCII drawing

above do not agree. Your ASCII drawing is a standard buck without an

output filter capacitor. I agree with your ASCII (with, possibly, the

requirement for an output filter capacitor) for a scheme which could work.

Grin.. sure... the ascii is a current boost and the first dropbox scribble is a current buck. I'm not sure what you mean about the ascii drawing... It's being fed from a current source.. so how can it be a 'standard buck'.
(The output is also a (DC) current.. so I can't really put a capacitor there.)

You should also note that the ascii has a current source feeding right into a capacitor! (But that really does seem analogous to the voltage boost where the voltage source feeds an inductor... both will 'rail out' if not part of the switching scheme.)

I'm having a lot of fun in my smps course. Maybe I'll have to build one someday and 'really' learn something :^)
I've often thought there might be a niche vacation market for geeks. Instead of going to the the ocean or mountains, you go to 'school' and intensely learn a new subject.
When I was at the FEL in Vanderbilt I went to "accelerator school"
http://uspas.fnal.gov/programs/1998/Stanford/courses/magneticsystems.shtml
(I think that might be it.)
It was great! Each night we'd sit around with a few beers and do the homework together.

George H.

 

[RobertMacy]

I'm having a lot of fun in my smps course. Maybe I'll have to build one
someday and 'really' learn something :^)
I've often thought there might be a niche vacation market for geeks.
Instead of going to the the ocean or mountains, you go to 'school' and
intensely learn a new subject.
When I was at the FEL in Vanderbilt I went to "accelerator school"
http://uspas.fnal.gov/programs/1998/Stanford/courses/magneticsystems.shtml
(I think that might be it.)
It was great! Each night we'd sit around with a few beers and do the
homework together.

George H.

Sounds like a great learning experience.

One can't help compare the 'basic'ness of Maxwell's Equations to Newton's
Laws of Physics in the sense that they work, and work well, but just as
for Newton, there might be one more thing out there? Didn't real progress
occur when observations that refuted Newton's Laws appear? Anybody know of
any observations that refute Maxwell's Equations? Or, are those
observations being swept under the carpet as erroneous or anomalies?

 

[Joerg]

[email protected] wrote:

[...]

As a consultant I get to wear shorts all summer long. When a web
conference with bigshots is coming up I have a "dress shirt on duty"
hanging in the lab closet

I just change into a new golf shirt. The good news about being a solo
consultant is that it's up to you. The bad news is also that it's up to
you.

Not always. For example, on Friday I had to wear a more formal attire
including a tie. The CEO that picked me up from the airport down south
also did. Well, I could have just not worn a tie but in that situation
is was customary and probably expected.

 

[RobertMacy]

Not always. For example, on Friday I had to wear a more formal attire
including a tie. The CEO that picked me up from the airport down south
also did. Well, I could have just not worn a tie but in that situation
is was customary and probably expected.

Noting the dangers of enemies and terrorists: I think the first
'important' people to stop wearing suits and ties were the leaders in
Israel. It's carried over a bit now to "low profile, no suit" else get
kidnapped etc. Plus, the allure of being SO rich that you can dress anyway
you please. So those of us with little money can now emulate wealth, by
dressing badly. Haberdashers everywhere have taken a hit.

 

[[email protected]]

[email protected] wrote:
[email protected] wrote:
[email protected] wrote:

[...]

Oops, I probably mixed you up with someone else. I thought it was stage
electronics for rock bands and stuff.

That was the last job. ;-) I've done a few career changes in the
last 10 years. Before that, one employer, oneish (perhaps two)
markets, but very different jobs every five to eight years.

5-8 years would be a bit much for me.

Takes that long to get a couple of generations of product out the
door.

I see it from two view points. One is the actual product and that often
doesn't look very good, both from a quality point of view and sometimes
also from an engineering point of view (flickering LED backlights
anyone?). Then from a people perspective and here talking to folks who
actually work in that field helps. Pretty much all of them reported
extreme pressure to keep NRE and R&D schedules down, which explains a
lot of the quality issues. To the point I wouldn't want to work there.
As a consultant maybe but niot if they'd demansd unrealistic timelines
like they often do from their employees.

Cost is everything but it's still no excuse for designing junk. In
that regard, it's not a lot different than what you've described that
you do.

There are automotive electronics that work quite well, mostly in
Japanese cars. In the end it boils down to the reliability ratings of
the various entities in the know.

Things change. A lot!

Sure, incremental change. Same in medical ultrasound which is my home
turf. But ... after we built a flagship product in the late 80's and the
satellite R&D location was closed afterwards I wasn't too unhappy that I
could jump into consulting for the first time, and do something else.




As a consultant I get to wear shorts all summer long. When a web
conference with bigshots is coming up I have a "dress shirt on duty"
hanging in the lab closet

In my last job I was the only one who wore long pants from April to
October. Everyone else in Engineering wore T-shirts year 'round. I
can't do that. I wear long-sleeved shirts (Oxfords, preferred) even
for mowing the lawn.

 

[RobertMacy]

Sure, when you're at their site. I wear a jacket when I'm doing video
Skype interviews with clients, too--especially lawyers. (It's
convenient that my drawing table is just across the room from a wall
full of books.)

Cheers

Phil Hobbs

A table? A wall of books? I didn't know you were into 'antiques'.

 

[Phil Hobbs]

A table? A wall of books? I didn't know you were into 'antiques'.

Since I turned 50 I'm entitled to wear a vintage plate myself.

And I love books. I have thousands of them, and have chucked out or
given away more thousands. I buy probably half a dozen a month, mostly
fine or VG condition used hardbacks. This month I got a book on
electromagnetic shock lines and one on hypersonic flow visualization.
Fun stuff.

You can see the aforementioned table and bookshelf in my virtual lab
tour, http://electrooptical.net/www/EOILab/EOILab.html .

It looks pretty much like that, except that I have a bunch more
furniture (two big lab benches and a table in the whiteboard/reception
area, plus some more in the admin/layout space). I also have way more
equipment. I've been meaning to replace the pictures, but the lab
hasn't been that clean since 2011.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[RobertMacy]

In my last job I was the only one who wore long pants from April to
October. Everyone else in Engineering wore T-shirts year 'round. I
can't do that. I wear long-sleeved shirts (Oxfords, preferred) even
for mowing the lawn.

Me too! I paint in a long sleeved Oxford shirt! even in AZ

My wife is still laughing about the time, on one of our sojourns including
Santa Cruz Boardwalk; I went to get us hotdogs from the boardwalk vendors
in a three piece suit, ...and was carrying my briefcase.

In 70's while at Stanford's Chapel for Christmas obaservance, one of my
colleagues wearing a rather worn sweatsuit [it WAS post hippy era] leaned
over and in attempting to ridicule my dress suit asked, "Why do you want
to dress like everyone else?" My reply, "Look around. I'm the ONLY suit
here. Look at you. Why do YOU want to dress like everyone else." And, yes.
EVERYBODY else was in totally casual attire.

 

[Joerg]

[...]

I see it from two view points. One is the actual product and that often
doesn't look very good, both from a quality point of view and sometimes
also from an engineering point of view (flickering LED backlights
anyone?). Then from a people perspective and here talking to folks who
actually work in that field helps. Pretty much all of them reported
extreme pressure to keep NRE and R&D schedules down, which explains a
lot of the quality issues. To the point I wouldn't want to work there.
As a consultant maybe but niot if they'd demansd unrealistic timelines
like they often do from their employees.

Cost is everything but it's still no excuse for designing junk. ...

Nobody seems to have told the executives that are ultimately responsible
for automotive electronics. Nearly all quality issues have their root
cause in upper management.

... In
that regard, it's not a lot different than what you've described that
you do.

Except I do not cut corners. Ever. If a client wants me to do that I
politely decline the whole assignment. It does happen but very rarely,
and those companies then do not even become clients of mine.

Things change. A lot!

That's what Maxim kept telling people

In my last job I was the only one who wore long pants from April to
October. Everyone else in Engineering wore T-shirts year 'round. I
can't do that. I wear long-sleeved shirts (Oxfords, preferred) even
for mowing the lawn.

I am just the opposite. I wear shorts and T-shirts as long as I can.
Only in really cold weather it's lumberjack shirts and jeans. For a
winter coat or jacket it almost would have to drop to below 0F.

 

[RobertMacy]

You can see the aforementioned table and bookshelf in my virtual lab
tour, http://electrooptical.net/www/EOILab/EOILab.html .

It looks pretty much like that, except that I have a bunch more
furniture (two big lab benches and a table in the whiteboard/reception
area, plus some more in the admin/layout space). I also have way more
equipment. I've been meaning to replace the pictures, but the lab
hasn't been that clean since 2011.

Cheers

Phil Hobbs

I have a voltmeter.

 

[Joerg]

I have a voltmeter.

I raise you one: I have a megacycle meter

This one:

http://www.ohio.edu/people/postr/bapix/Dip_59.htm

 

[John S]

You've got the gist of the problem. I made up some of the numbers and
didn't notice they didn't quite correlate. But you see the premise for
the problem.

To maintain some semblance of efficiency, I can't simply 'shunt' unused
power off.

So, you cannot provide a short circuit for the current source? You are
in deep trouble.

 

[John S]

Grin.. sure... the ascii is a current boost and the first dropbox
scribble is a current buck. I'm not sure what you mean about the
ascii drawing... It's being fed from a current source.. so how can
it be a 'standard buck'. (The output is also a (DC) current.. so I
can't really put a capacitor there.)

I don't really care about the source. It's max voltage is specified at
100V, no? It' max (and constant) current is specified at .05A, no?

There is therefore a maximum power output capability of 5W. No?

It does not matter what topology you use, you cannot get more out than
you put in. Where am I wrong here?

You should also note that the ascii has a current source feeding
right into a capacitor! (But that really does seem analogous to the
voltage boost where the voltage source feeds an inductor... both
will 'rail out' if not part of the switching scheme.)

Who cares? You cannot amplify power (in this particular scenario). If
the output is 5V, what is the current? I think maybe 1A. That's current
amplification if you put 100V into a buck switcher at 50mA and regulate
the output to 5V.

This is not what I am suggesting, so see my other post.

(snipped fun times)

 

[Joerg]

So, you cannot provide a short circuit for the current source? You are
in deep trouble.

The current source won't be 100% efficient. What Robert probably wants
to avoid is having to shunt some of the current to ground. This will
cause loss because another part of that current is used to make a
different secondary current. That means there is going to be voltage
drop. If you shunt past that -> wasted energy.

The ideal situation would be, for example, a flyback that regulates to
an output current that has the desired ratio to the input current and at
that point sets its input impedance in such a way that it uses up all
the current coming in, wasting none. Sounds feasible.

Of course, with AC Robert would need a rectifier and, if AC is to be
delivered at the output, a FET bridge.