Driver to drive?

[Vadim Borshchev]

On 13 Oct 2004 01:34:28 -0700, Al Hastings <magic4you@hotmail.com> wrote:

Does anyone know any devices (such as ion ray guns) that can push
metal away instead in your direction like an electromagnet?

http://www.powerlabs.org

Have fun!

Vadim

 

Note also that this project is an _extension_ of an existing project.
I'm simply making it more general-purpose. The original project was to
record a running telemetry stream on the audio track of a camcorder, so
that an external box next to the TV set could decode the telemetry and
display it while the video was being played back. The requirement was
not to modify the camcorder at all.

How about a onboard pc or dsp that compress any arbitrary numbers of video and
audio streams + telemetry data ?

It all depends on the amount of telemetry data and budget I guess =)

 

[John Hudak]

comments below..

Terry Given wrote:

Joerg wrote:

Hi All,

Micro controllers can be used to drive a switcher from their PWM
output. Most of us know how to do that. But my question: Is there some
nifty literature on the web or elsewhere about all the trade-offs this
entails?

What I mean are trade-offs with respect to PWM granularity, for
example. Suppose the counter runs off 5MHz. In order to arrive at
reasonable cost for the magnetics the PWM output needs to be, say,
300KHz or higher. That leaves only 4 bits of granularity. So it would
idle like a Harley with worn spark plugs, something that may be ok.
Then there is the feedback. Most uCs with an on-board ADC are out of
price range so slope may have to do. On top of that there may be a
limit of one slope conversion unless eternal muxing is done.

Current mode is another topic. Tough to do on a uC but then again if
one can measure both current and voltage the uC "knows" where about
the PWM should be. But it's all not very precise. Then there is the
issue of making the code that runs the PWM safe and fast enough. After
all, one minor hangup in this area could result in a plume of smoke.
Next, there is the trend to ever lower VCC levels which renders the
task of turning on a FET hard enough non-trivial.

Regards, Joerg


Hi Joerg,

you can dither to increase the resolution, but it doesnt gain you much.
AFAIK the answer is more clock speed (there are cunning tricks to
increase resolution, but all require a DIY pwm generator and a faster
clock).

micro sample rate is usually the killer. I am designing a drive at the
moment using a TI dsp that clocks at 150MHz, has 16 1us ADCs etc. Full
digital control, BUT hardware peak current limit/trip, cross-conduction
control and DC bus voltage limiting. software never works properly, and
programmers do stuff like step-to-breakpoint which is a great way of
applying DC to a machine

think synchronous sampling for current measurement - if you use
symmetric PWM (triangle not sawtooth reference wave, ie count up then
count down) then you always know where the middle of the pulse is, and
here is a good place to sample current as it is furthest away from
switching edges. also serves to remove switching-frequency ripple from
current measurement.


I once had to use a nasty little atmel micro (no multiply instruction
?!) for a 400W smps - it was a customers design I had to make go. They
Really? from what I recall, they all did, cept the very early one(s)...
had a 3-phase smps (no particular reason, and not cost-effective) so 6x
output ripple ie can tolerate low output inductance. They switched
T0-220 IGBTs at about 2kHz, with a loop time of 100ms and a 10uH output
inductor; cpu crystal was 4MHz. Needless to say, first I had to up the
switching frequency. They refused to change micros, so I made a 3-phase
pwm generator (7-bit parallel duty cycle input) with a ROM and a pair of
counters (< $1), interlock included. Changed to FETs, upped Fswitch to
cleaver, but 7 bits?
100kHz and increased xtal to 12MHz. I also used the current limit
circuitry inherent in the (IIRC) IR2110 gate driver IC, and measured the
DC bus voltage for feed-forward. Oh, there was no isolation either - the
output "0V" was -200V wrt protective earth. Probably not a good
marketing strategy as most customers will die the first time they touch
it.....
No, definitely not a good idea-who said marketing has the background to

make such a decision?, Forgive me but why would your engineering ethics
allow this to happen?
(Yes, I've refused to do designs where there is a risk of a health
hazard...I'd consider electrocution a health hazard)

Static psu performance with the new hardware was very good. But they
still closed the digital loop at 100ms, so dynamic behaviour was
atrocious. Using the shitty micro I came up with a "novel" PI controller
with feed-forward that didnt use a multiply instruction (not easy!), and
with the control loop running at 5kHz the dynamic performance was OK.
The final design was about 2x larger and more expensive than a
conventional 400W smps, but they were happy and paid my bill (note: I
didnt make it any larger, my stuff fitted into the existing design).

Never again will I do such a silly thing. Using the shitty micro I mean,
not making a stupid design work. reminds me of another job, where the
first team used a $50 8051-derivative micro from Cygnal (68-pin,
lightspeed operation etc). We used a $4 8051 derivative, and did the
same job.

cheers
Terry

 

[Doug Goncz]

Today I connected the main phase to AC and spun the rotor. It continued to spin
while energized.

Later, I will try energizing the split phase with AC, driving the shaft with
the pedals and taking AC from the main phase.

Thanks to knight in shining armor Terry.

Off to the library or to ieee.org....


Yours,
Doug Goncz ( ftp://users.aol.com/DGoncz/incoming )
Student member SAE for one year.
I love: Dona, Jeff, Kim, Mom, Neelix, Tasha, and Teri, alphabetically.
I drive: A double-step Thunderbolt with 657% range.

 

[Dave]

"Tim Wescott" <tim@wescottnospamdesign.com> wrote in message
news:10mofeo3eerg791@corp.supernews.com...

Dave wrote:

Well, I probably knew this at one time, but then I went into the
business of
repairing computers and associated equipment (simple troubleshooting and
board-swapping) and did that for 12 years before sleeping for the last
ten
(with a sleep disorder). Now I find I have forgotten everything but
Ohm's
Law (and am beginning to wonder about that.) So, I have some
questions...

Recently bought a copy of Introduction to Radio Frequency Design
(Hayward)
and discovered just how ignorant I am now. In the first few pages there
are
a couple of symbols I don't recognize. The first is simply an ampersand
(&
symbol) but it's between a couple of variables in an equation. What is
that
called in this capacity, and where should I look to find out what it
means
(again, in this capacity.) The second is simply two vertical lines in
parrallel, rather like the side-bars of a capital H but without the
cross-bar in the middle. Again, what is this called and where should I
look
for information on it? (Maybe a capital pi symbol? But what does it
*mean*?) This last reminds me of the three dots in a small triangle,
used
in logic to mean "therefore," but I don't even remember where to look to
check out that possibility. Totally ignorant. (Shaking head.)

Thanks in advance for any help. I really hate to admit being this
stupid,
but I need to know, so...

Dave
db5151@hotmail.com


What pages? What equation numbers? I don't see this is my copy ("first
ARRL edition").

The only place I know where an ampersand is used between variables is in
computer languages related to C where it means "and" (either bitwise or
logical depending on the language). A vertical bar, "|", in C means
bitwise or and two "||" mean logical or -- but that doesn't go in an RF
book!

Two vertical lines placed closely between two impedances often mean
those impedances taken in parallel, so if R1 and R2 are both 100 ohms
then R1+R2 = 200 ohms, and R1 || R2 = 50 ohms. _This_ I could believe
seeing. Pairs of vertical lines bracketing a vector quantity, ||x||
mean the vector "norm", usually the sum of the square of its elements,
but sometimes something different if the mathematician in question
notices that you seem to be understanding the material -- and I wouldn't
expect it in Hayward's book.

Three dots in a small triangle does indeed mean "therefore". Sometimes
you'll see two horizontal parallel lines with an arrowhead, like "=>",
that technically means "it follows" but is used as "therefore",
particularly on blackboards where the three dots are hard to write...

--

Shit. I really am an idiot. It wasn't in Haywards book at all, but was in
something I got off the net that I was studying along with Hayward's book.
Sorry. *Really* didn't mean to be *that* stupid.

What I described is in a PDF at the following website:
http://www.eng.fsu.edu/~ejaz/EEL3300L/lab8.pdf

The ampersand and verticle parrallel lines are on page 3. On page 1 is a
capital B and a large scripted f which I also wonder about. I assume the
capital B is for beta, but the f looks like something I would see in a
function declaration rather than an electronics equation. On page 2, down
near the bottom, is the same scripted f, this time in subscript to a V for
voltage. All of this is unfamiliar to me, and I would really appreciate any
help anyone could offer on it.

I apologize for the mistake of saying it was in Wes Hayward's book. I was
trying to study all of this spread out on a table while with my wife at her
office, and posted about it that night after getting home. Did not intend
to confuse the issue..

Thanks for trying to help.

Dave
db5151@hotmai.com

 

[Dave]

"Paul Burridge" <pb@notthisbit.osiris1.co.uk> wrote in message
news:5e1qm09rg488psudqke08kelvio8q9beqi@4ax.com...

On Tue, 12 Oct 2004 15:04:07 -0500, "Dave" <db5151@hotmail.com> wrote:

Well, I probably knew this at one time, but then I went into the business
of
repairing computers and associated equipment (simple troubleshooting and
board-swapping) and did that for 12 years before sleeping for the last
ten
(with a sleep disorder). Now I find I have forgotten everything but
Ohm's
Law (and am beginning to wonder about that.) So, I have some
questions...

Snip!

There are several sites on the web that provide the info you seek.
Just try Googling under "mathematical symbols" and you'll be spoilt
for choice.
--

"What is now proved was once only imagin'd." - William Blake, 1793.

Could not find any of this, even with Google. Really beginning to wonder
now...

Dave
db5151@hotmail.com

 

[Dave]

"Terry Pinnell" <terrypinDELETE@THESEdial.pipex.com> wrote in message
news:06lpm09odf8m2vmddh6sju9dc3ene84un3@4ax.com...

"Dave" <db5151@hotmail.com> wrote:

snip
In the first few pages there are
a couple of symbols I don't recognize. The first is simply an ampersand
(&
symbol) but it's between a couple of variables in an equation.

Without seeing the context, impossible to be sure. But my first guess
would be a logical AND. Is it something like 'A&B' or 'X&Y', and were
logic signals being discussed?

The second is simply two vertical lines in
parrallel, rather like the side-bars of a capital H but without the
cross-bar in the middle.

With the same caveat about context, that normally means 'in parallel'.
So for example 'Ra||Rb' would mean the two resistors Ra and Rb in
parallel. And '8||8' would be 4 if the context was resistance, or 16
if capacitance.

--
Terry Pinnell
Hobbyist, West Sussex, UK

Please see my reply to Tim Wescott for a clearer description of the context
and usage.

Thanks for the reply.

Dave
db5151@hotmail.com

 

[Tim Wescott]

Dave wrote:

"Tim Wescott" <tim@wescottnospamdesign.com> wrote in message
news:10mofeo3eerg791@corp.supernews.com...

Dave wrote:


Well, I probably knew this at one time, but then I went into the

business of

repairing computers and associated equipment (simple troubleshooting and
board-swapping) and did that for 12 years before sleeping for the last

ten

(with a sleep disorder). Now I find I have forgotten everything but

Ohm's

Law (and am beginning to wonder about that.) So, I have some

questions...

Recently bought a copy of Introduction to Radio Frequency Design

(Hayward)

and discovered just how ignorant I am now. In the first few pages there

are

a couple of symbols I don't recognize. The first is simply an ampersand

(&

symbol) but it's between a couple of variables in an equation. What is

that

called in this capacity, and where should I look to find out what it

means

(again, in this capacity.) The second is simply two vertical lines in
parrallel, rather like the side-bars of a capital H but without the
cross-bar in the middle. Again, what is this called and where should I

look

for information on it? (Maybe a capital pi symbol? But what does it
*mean*?) This last reminds me of the three dots in a small triangle,

used

in logic to mean "therefore," but I don't even remember where to look to
check out that possibility. Totally ignorant. (Shaking head.)

Thanks in advance for any help. I really hate to admit being this

stupid,

but I need to know, so...

Dave
db5151@hotmail.com



What pages? What equation numbers? I don't see this is my copy ("first
ARRL edition").

The only place I know where an ampersand is used between variables is in
computer languages related to C where it means "and" (either bitwise or
logical depending on the language). A vertical bar, "|", in C means
bitwise or and two "||" mean logical or -- but that doesn't go in an RF
book!

Two vertical lines placed closely between two impedances often mean
those impedances taken in parallel, so if R1 and R2 are both 100 ohms
then R1+R2 = 200 ohms, and R1 || R2 = 50 ohms. _This_ I could believe
seeing. Pairs of vertical lines bracketing a vector quantity, ||x||
mean the vector "norm", usually the sum of the square of its elements,
but sometimes something different if the mathematician in question
notices that you seem to be understanding the material -- and I wouldn't
expect it in Hayward's book.

Three dots in a small triangle does indeed mean "therefore". Sometimes
you'll see two horizontal parallel lines with an arrowhead, like "=>",
that technically means "it follows" but is used as "therefore",
particularly on blackboards where the three dots are hard to write...

--




Shit. I really am an idiot. It wasn't in Haywards book at all, but was in
something I got off the net that I was studying along with Hayward's book.
Sorry. *Really* didn't mean to be *that* stupid.

What I described is in a PDF at the following website:
http://www.eng.fsu.edu/~ejaz/EEL3300L/lab8.pdf

The ampersand and verticle parrallel lines are on page 3. On page 1 is a
capital B and a large scripted f which I also wonder about. I assume the
capital B is for beta, but the f looks like something I would see in a
function declaration rather than an electronics equation. On page 2, down
near the bottom, is the same scripted f, this time in subscript to a V for
voltage. All of this is unfamiliar to me, and I would really appreciate any
help anyone could offer on it.

I apologize for the mistake of saying it was in Wes Hayward's book. I was
trying to study all of this spread out on a table while with my wife at her
office, and posted about it that night after getting home. Did not intend
to confuse the issue..

Thanks for trying to help.

Dave
db5151@hotmai.com


I think the ampersand is just that professor's confusing attempt to make

things clear (I read it as "R_1 in parallel with R_2, or R_B"), the
vertical parallel lines indicate resistors in parallel.

The "Bf" is forward beta, and is usually denoted with a real, actual
Greek letter beta and a subscripted 'f'; that guy really needs to learn
how to use an equation editor. The "V_f" (he actually managed a real
subscript that time!) is the forward diode drop of the transistor -- one
often just assumes a number like 0.65V and designs as if it won't
change, which works as long as you remember that it _does_ change with
temperature.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

 

[Ken Smith]

In article <mm1bd.13$0O.676@news.xtra.co.nz>,
Terry Given <my_name@ieee.org> wrote:

Ken Smith wrote:

In article <wd2dndhgwIuaHfHcRVn-vQ@comcast.com>,
Dave VanHorn <dvanhorn@cedar.net> wrote:

SEVEN bits.. damned new glasses..


One bit would be enough if the output filter cap is large enough.



did I mention they had no output cap? the open-circuit voltage didnt
look so nice

I guess it depends on whether you like ratty looking waveforms. I think
some of them are kind of cute.

In theory, you can make a Cuk converter with no output cap and no ripple.

--
--
kensmith@rahul.net forging knowledge

 

[john jardine]

"Joerg" <notthisjoergsch@removethispacbell.net> wrote in message
news:VB_ad.12234$nj.8581@newssvr13.news.prodigy.com...

[-]

I usually go with the 40106 for a standalone solution. It doesn't really
want to do more than 200KHz but often that's just enough. This way I get
a six-pack for the money and it works without pre-regulation from 12V
and 9V batteries. Under 6V it becomes kind of sluggish, then it's off to
the HC series.

Regards, Joerg

http://www.analogconsultants.com

For fun, I had a 74HC132 switcher running at 4MHz the other week. Nice thing
is (as you said) the magnetics can cost nothing other than a bit of wire.
regards
john

 

[Doug Goncz]

Dear Terry,

Would you think the Surplus Center's #10-1134 225 rpm split phase capacitor run
impedance protected ceiling fan motor would make a decent human powered
generator?

http://surpluscenter.com/item.asp?UID=2004101315154496&catname=&qty=1&item
=10-1134

Oh, dear, that link looks long. Is it breaking in any reader's reader?

I have had the shaft of this motor machined to accept my standard 8 tooth
pinion for bicycle chain, the same one I use on the DC motor/generator. It is
mounted over the cranks, near them, and chain wrap is low, only some 30
degrees, to reduce pedaling drag and improve chain retention over bumps. The
drive cog is 51 teeth, matching the custom gearing on the right, giving a motor
speed near 225 rpm, with variations in peadling speed right about the human
range of, for non-racers like me, 40-90 rpm producing proportional changes in
motor speed.

I can try two things.

One, run an inverter from the road wheel driven DC motor generator, and excite
one phase of the motor, drawing power from the other when the cranks are
turned, possibly, through coupling, even when they are not turned.

Two, use the DC supply to hit both phases of the motor with the secondary
winding's phase shift capacitor in place, in order to excite the rotor, and
then open the DC circuit, continue pedaling, and place the load on line.
Lindsay Technical Books has a publication, Alternator Secrets, that says this
will work. The author claims a split phase motor with phase shift capacitor is
suited to generator operation.

Googling

"self-excited induction generators"

From: Terry Given my_name@ieee.org

produces 185 hits, and you have my deepest thanks for naming this beast.

IEE trans. industry apps. has published dozens (prob. hundreds) of
papers over the last few years on SEIGs. Just recently they published a
couple of papers on drives for split-phase IMs - with an active drive,
no caps are required.

Hot on the trail....

As for generator power factor etc - the "generator" has some finite
(inductive) output impedance - often up to 30%. choose the IM wisely
grasshopper...

Yes, this impedance protected motor is perfectly shaped for bicycle
application, but has high impedance. I am going with the shape to start,
finding key components like that is my business, and making them work my
profession.

But hey, anybody, save me some time here if you can. If it can't work, say why.

people who build their own motors soon discover that building a reliable
motor isnt that easy.

Yes, I find the one-moving part plus bearings idea of this motor suitable for
my intended applciation. Much less complicated than the DC generator it is to
replace.


Yours,
Doug Goncz ( ftp://users.aol.com/DGoncz/incoming )
Student member SAE for one year.
I love: Dona, Jeff, Kim, Mom, Neelix, Tasha, and Teri, alphabetically.
I drive: A double-step Thunderbolt with 657% range.

 

[Joerg]

Hi John,

I did, possibly, the world's worst switcher a while back. It has a
3-phase, roughly 240 vdc rectified source driving a capacitor bank
through some opto-coupled power fets and a huge military-type
bolt-down 250 watt power resistor; we don't need no stinkin'
inductors! ...

Ouch. That must have been before the oil price hit $50 a barrel

Regards, Joerg

http://www.analogconsultants.com

 

[Joerg]

Hi Chris,

This may seem unrelated but it isn't. Several manufacturers have built pure
sinewave DC/AC inverters using *just* PICs, mosfet drivers, mosfets and
transformers. Nothing else. No PWM controllers. As these things have to
tolerate truck, boat and caravan owners connecting them to just about anything
possible the protection on these *has* to be good.

They have shown themselves to be *very* reliable.

So it clearly *is* feasable though I've never looked into it in any detail.


Interesting that you mentioned that. I didn't know they used PICs in

these inverters. Also, I googled a lot to find schematics for one of
these large inverters just to marvel at but came up dry every time. It
probably is a tight lipped community.

It seems the pure sine inverters are not for the common people since
everything that I saw for boats and other uses did a rather crude
approximation. Then again, these were all in the sub-$200 class. I guess
a PIC may already be too large of an investment here.

Regards, Joerg

http://www.analogconsultants.com

 

[Charles Schuler]

Tell us what you are trying to do. If you want to learn more about radio
frequencies, the ARRL handbook can't be beat.

 

[Paul Burridge]

On Wed, 13 Oct 2004 11:59:18 -0500, "Dave" <db5151@hotmail.com> wrote:

Could not find any of this, even with Google. Really beginning to wonder
now...

Sigh...
Post this link into your browser:

http://whatis.techtarget.com/definition/0,,sid9_gci803019,00.html
--

"What is now proved was once only imagin'd." - William Blake, 1793.

 

[CBFalconer]

JeffM wrote:

pbdelete@spamnuke.ludd.luthdelete.se.invalid

A 44-character screen name with no spaces.
Congratulations. You get the booby prize.
Ever thought about just using "pb"?

Was your wife mean to you this morning? The dog? Kids fail to
show the proper respect?

--
Chuck F (cbfalconer@yahoo.com) (cbfalconer@worldnet.att.net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home.att.net> USE worldnet address!

 

[Spehro Pefhany]

On Wed, 13 Oct 2004 21:22:38 GMT, the renowned Joerg
<notthisjoergsch@removethispacbell.net> wrote:

Hi John,

I did, possibly, the world's worst switcher a while back. It has a
3-phase, roughly 240 vdc rectified source driving a capacitor bank
through some opto-coupled power fets and a huge military-type
bolt-down 250 watt power resistor; we don't need no stinkin'
inductors! ...

Ouch. That must have been before the oil price hit $50 a barrel

I worked out a similar "brute force" design. The efficiency wasn't all
that bad. Throwing away two hundred watts in resistors worst case and
getting a couple kW out of it is still close to 90% efficiency.

 

[John Larkin]

On Mon, 11 Oct 2004 00:19:44 -0700, "Richard Henry" <rphenry@home.com>
wrote:

"John Larkin" <jjlarkin@highlandSNIPtechTHISnologyPLEASE.com> wrote in
message news:6njjm0d61uu7h2er1h39c30i8lup4nlouj@4ax.com...

Agreed, all the things I mentioned were clearly unconstitutional, and
were morally wrong, and most were stopped by the courts. I think the
courts will still protect us from excesses. Remarkably, no
administration or congress that I know of has ever defied a Supreme
Court ruling.

Chuckle

My bad week at the airport:

On the trip out, I was "selected" for the full treatment: metal-detector
wand, full-body frisk (not, unfortunately, by the young lady inspector
present) and shoes placed in some sort of detection device.

On the trip back three days later, I left my ticket on a table (thoughtfully
provided so travellers can get all their papers and belongings in proper
order for inspection) on the wrong side of the security screen. As soon as
I noticed, so did the security people, and they paged me to come back up
against the stream to get it. A word of advice: don't move upstream. I was
physically barred from doing so by a civilian security agent, and threatened
by an armed National Guardsman for the offense of placing my briefcase on
the floor and walking the dozen or so feet back upstream to the point where
I was stopped.

My travelling companion, an Anapolis graduate and Navy Reserve Commander,
was highly amused. I was not.

The overall irony is that the purpose of the trip was to visit a vendor who
was assisting us in the design of a device to detect (real) terrorist
weapons.

Well, at least you didn't spend 16 years in a forced-labor camp. Or
have to sleep in the airport for six days waiting for a plane to be
available, because you can't afford the bribes. Both of which happen
to people who have *real* problems.

John

 

[Terry Given]

John Hudak wrote:

comments below..

Terry Given wrote:

Joerg wrote:

Hi All,

Micro controllers can be used to drive a switcher from their PWM
output. Most of us know how to do that. But my question: Is there
some nifty literature on the web or elsewhere about all the
trade-offs this entails?

What I mean are trade-offs with respect to PWM granularity, for
example. Suppose the counter runs off 5MHz. In order to arrive at
reasonable cost for the magnetics the PWM output needs to be, say,
300KHz or higher. That leaves only 4 bits of granularity. So it would
idle like a Harley with worn spark plugs, something that may be ok.
Then there is the feedback. Most uCs with an on-board ADC are out of
price range so slope may have to do. On top of that there may be a
limit of one slope conversion unless eternal muxing is done.

Current mode is another topic. Tough to do on a uC but then again if
one can measure both current and voltage the uC "knows" where about
the PWM should be. But it's all not very precise. Then there is the
issue of making the code that runs the PWM safe and fast enough.
After all, one minor hangup in this area could result in a plume of
smoke. Next, there is the trend to ever lower VCC levels which
renders the task of turning on a FET hard enough non-trivial.

Regards, Joerg



Hi Joerg,

you can dither to increase the resolution, but it doesnt gain you
much. AFAIK the answer is more clock speed (there are cunning tricks
to increase resolution, but all require a DIY pwm generator and a
faster clock).

micro sample rate is usually the killer. I am designing a drive at the
moment using a TI dsp that clocks at 150MHz, has 16 1us ADCs etc. Full
digital control, BUT hardware peak current limit/trip,
cross-conduction control and DC bus voltage limiting. software never
works properly, and programmers do stuff like step-to-breakpoint which
is a great way of applying DC to a machine

think synchronous sampling for current measurement - if you use
symmetric PWM (triangle not sawtooth reference wave, ie count up then
count down) then you always know where the middle of the pulse is, and
here is a good place to sample current as it is furthest away from
switching edges. also serves to remove switching-frequency ripple from
current measurement.


I once had to use a nasty little atmel micro (no multiply instruction
?!) for a 400W smps - it was a customers design I had to make go. They

Really? from what I recall, they all did, cept the very early one(s)...

had a 3-phase smps (no particular reason, and not cost-effective) so
6x output ripple ie can tolerate low output inductance. They switched
T0-220 IGBTs at about 2kHz, with a loop time of 100ms and a 10uH
output inductor; cpu crystal was 4MHz. Needless to say, first I had to
up the switching frequency. They refused to change micros, so I made a
3-phase pwm generator (7-bit parallel duty cycle input) with a ROM and
a pair of counters (< $1), interlock included. Changed to FETs, upped
Fswitch to

cleaver, but 7 bits?

I ended up with 8MHz xtal (oops I said 12 b4) and 50kHz pwm, so 160
counts per period = 7.3 bits. I was only interested in 0-120 degrees of
phase shift, so needed at least 6 bits of phase shift input to ROM.

100kHz and increased xtal to 12MHz. I also used the current limit
circuitry inherent in the (IIRC) IR2110 gate driver IC, and measured
the DC bus voltage for feed-forward. Oh, there was no isolation either
- the output "0V" was -200V wrt protective earth. Probably not a good
marketing strategy as most customers will die the first time they
touch it.....

No, definitely not a good idea-who said marketing has the background to
make such a decision?, Forgive me but why would your engineering ethics
allow this to happen?
(Yes, I've refused to do designs where there is a risk of a health
hazard...I'd consider electrocution a health hazard)

obviously I wasnt clear enough: I was brought in to "review" their
allegedly working design. that was the first thing I found, when I
reviewed creepage/clearance/insulation. Needless to say I went to great
lengths to point out that it was lethal, illegal and of course downright
stupid. These guys knew nothing at all, yet were convinced they were
designers. It turned into the job from hell, but taught me a lot:
specifying deliverables, charging for extras (like being roped into
designing the heatsinks & enclosure) and most importantly, steering
clear of idiots Phrases like "We dont need a contract specifying
deliverables, just do..." now ring alarm bells. They went broke a few
years later...

Static psu performance with the new hardware was very good. But they
still closed the digital loop at 100ms, so dynamic behaviour was
atrocious. Using the shitty micro I came up with a "novel" PI
controller with feed-forward that didnt use a multiply instruction
(not easy!), and with the control loop running at 5kHz the dynamic
performance was OK. The final design was about 2x larger and more
expensive than a conventional 400W smps, but they were happy and paid
my bill (note: I didnt make it any larger, my stuff fitted into the
existing design).

Never again will I do such a silly thing. Using the shitty micro I
mean, not making a stupid design work. reminds me of another job,
where the first team used a $50 8051-derivative micro from Cygnal
(68-pin, lightspeed operation etc). We used a $4 8051 derivative, and
did the same job.

cheers
Terry

 

[John Larkin]

On 13 Oct 2004 21:42:19 GMT, chrisgibbogibson@aol.com
(ChrisGibboGibson) wrote:

There is a small unit made by TBS in Holland which uses 1 PIC, 2 IR2110 drivers
and a handfull of mosfets. This then feeds a line frequency transformer. That's
all there is in the box. Pure sinewave output. Fully protected against
overload. Very fast regulation. Very reliable.

What smooths the chop into a sine? Leakage inductance in the
transformer?

John