Looking for EE, switching power supp, class D audio

[Olin Lathrop]

I'm looking for a hardware engineer to do most of the basic work of
designing class D audio power amplifiers.  Experience with switching power
supplies is important.  Experience with class D audio is a plus but not
required.  High level guidance will be available from experts, but you will
be doing the actual design, manage getting boards made, prototypes built,
debug them, etc.  Must be local to Littleton Massachusetts.

If you are interested or know anyone that is, call me at [phone].


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[William "Chops" Westfield]

Just out of curiosity:

> I'm looking for a hardware engineer to do most of the basic work of
> designing class D audio power amplifiers.

Hasn't this reached the stage of "pick a class D amp chip and follow  
the manufacturer recommendations ?

> Experience with switching power supplies is important.

Why?  I mean, I see how they're similar, and if you had someone who  
didn't have any class D amp experience, a good background in SMPS  
would be knowledge in the right direction.  But once someone has  
"specialized" in class D amps, do they still need the SMPS  
background?  (or are you looking for a class D amp as a product  
(including power supply, designed for max efficiency overall) instead  
of as a module on a board that already has a supply?)

BillW

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[Herbert Graf-2]

On Fri, 2008-12-12 at 09:47 -0800, William "Chops" Westfield wrote:
> Just out of curiosity:
>
> > I'm looking for a hardware engineer to do most of the basic work of
> > designing class D audio power amplifiers.
>
> Hasn't this reached the stage of "pick a class D amp chip and follow  
> the manufacturer recommendations ?

I'd have to agree. Even for the more broad SMPS supply world actually
designing an SMPS is becomming less and less necessary, in many cases
just use the online tools to select which chip is best, and follow the
reference design.

That's not to say that bringup doesn't require skill, and I believe it's
here that the expertise is most valuable. Getting even a reference SMPS
design physically working can sometimes be a challenge.

TTYL

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[Olin Lathrop]

William Chops" Westfield" wrote:
>> I'm looking for a hardware engineer to do most of the basic work of
>> designing class D audio power amplifiers.
>
> Hasn't this reached the stage of "pick a class D amp chip and follow
> the manufacturer recommendations ?

No.  In any case, someone still has to actually do the work.

>> Experience with switching power supplies is important.
>
> Why?  I mean, I see how they're similar,

It has nothing to do with similarity with class D amplifiers.

> But once someone has
> "specialized" in class D amps, do they still need the SMPS
> background?

Probably not to design just a raw class D amp.

> (or are you looking for a class D amp as a product
> (including power supply, designed for max efficiency overall) instead
> of as a module on a board that already has a supply?)

I listed the qualifications that would be most useful for this job.  That
should be enough for someone to get a pretty good idea whether they want to
persue it or not.  I don't plan on publicly supplying additional
information.


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[Olin Lathrop]

Herbert Graf wrote:
>> Hasn't this reached the stage of "pick a class D amp chip and follow
>> the manufacturer recommendations ?
>
> I'd have to agree. Even for the more broad SMPS supply world actually
> designing an SMPS is becomming less and less necessary, in many cases
> just use the online tools to select which chip is best, and follow the
> reference design.

For some level or performance, cost, efficiency, and board space this is
true, but not for all.


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[Xiaofan Chen]

On Sat, Dec 13, 2008 at 3:16 AM, Olin Lathrop <olin_piclist@...> wrote:
> Herbert Graf wrote:
>> I'd have to agree. Even for the more broad SMPS supply world actually
>> designing an SMPS is becoming less and less necessary, in many cases
>> just use the online tools to select which chip is best, and follow the
>> reference design.
>
> For some level or performance, cost, efficiency, and board space this is
> true, but not for all.

Unfortunately the performance, cost, efficiency, and board space
are often issues involved in my world. So it is still good to have
some knowledge in SMPS. I lack the experiences in magnetics
design, so I have to rely on another expert when customized
part is necessary.

For example, I could not find any good chip for the universal
power supply sensor application (12-240V DC and 20-240V AC,
very low power, just to power a 5V PIC and a 9V relay and some
low power analog stuff). So I had to develop the buck converter
using transistors/MOSFETs for two designs.

And to choose the right chip can be challenging sometimes.
For example, last time we talked to many vendors to get
a high efficiency synchronous buck converter design. Many
vendors have good chips, but to meet the efficiency and
space constraint, only Linear Tech has a good chip. And
at the layout stage, we had to be very careful since the
reference board does not have the space constraint like
what we had. It was a success and it was rewarding though
since it can be replicated to other similar design across
the company.

On the other hand, I could see that in many applications,
the way to go is to get a ready-made module/boards. And
in many situations, it makes sense to outsource to power
supply module to 3rd party specialists if ready-made
modules are not available.

Xiaofan
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[Olin Lathrop]

Xiaofan Chen wrote:

>>> Even for the more broad SMPS supply world
>>> actually designing an SMPS is becoming less and less necessary, in
>>> many cases
>>> just use the online tools to select which chip is best, and follow
>>> the reference design.
>>
>> For some level or performance, cost, efficiency, and board space
>> this is true, but not for all.
>
> Unfortunately the performance, cost, efficiency, and board space
> are often issues involved in my world.

Exactly.  It seems every power supply is different in the range of input
voltages, output voltage, amount of ripple tolerated, output current,
inefficiency tolerated, and of course the usual tradeoffs between cost,
board space, cooling requirements, standby power, etc, etc, etc.  Then
startup is a whole other issue that off the shelf simple PWM chips are
usually bad at or tricky to make work right over a wide input voltage range.
Too many casual SMPS designers aren't even aware there are special issues
there.

Anybody that thinks they don't really need to know about switching power
supplies to plunk one on the board from the app note doesn't belong there
and is headed for trouble.  The guy who designed the original product for a
local startup company had this attitude.  He grabbed a "simple switcher"
from National (great marketing, but their switchers aren't more or less
simple than others) and copied the circuit from some app note.  Both the
inductor and FET were always hot, usually just about where you couldn't
touch them for more than a second, even though the whole unit only took
about 5W.  I was told that when people pointed this out to him he would only
respond that the circuit was right out of the app note and it therefore
couldn't be wrong.  He was fired and I was brought in.


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[phone].  Gold level PIC consultants since 2000.
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[Russell McMahon]

> simple than others) and copied the circuit from some app note.  Both the
> inductor and FET were always hot, usually just about where you couldn't
> touch them for more than a second, even though the whole unit only took
> about 5W.

Apart from the efficiency issues, if that was a powdered iron core inductor
(which it probably wasn't) it's life would drop by an order of magnitude or
wore over what was expected. And many 'designers' don't realise that
powdered iron cores can have significantly sall lifetimes.


        Russell

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[John Day-5]

At 10:00 AM 12/13/2008, Olin Lathrop wrote:

>Xiaofan Chen wrote:
> >>> Even for the more broad SMPS supply world
> >>> actually designing an SMPS is becoming less and less necessary, in
> >>> many cases
> >>> just use the online tools to select which chip is best, and follow
> >>> the reference design.
> >>
> >> For some level or performance, cost, efficiency, and board space
> >> this is true, but not for all.
> >
> > Unfortunately the performance, cost, efficiency, and board space
> > are often issues involved in my world.
>
>Exactly.  It seems every power supply is different in the range of input
>voltages, output voltage, amount of ripple tolerated, output current,
>inefficiency tolerated, and of course the usual tradeoffs between cost,
>board space, cooling requirements, standby power, etc, etc, etc.  Then
>startup is a whole other issue that off the shelf simple PWM chips are
>usually bad at or tricky to make work right over a wide input voltage range.
>Too many casual SMPS designers aren't even aware there are special issues
>there.
>
>Anybody that thinks they don't really need to know about switching power
>supplies to plunk one on the board from the app note doesn't belong there
>and is headed for trouble.  The guy who designed the original product for a
>local startup company had this attitude.  He grabbed a "simple switcher"
>from National (great marketing, but their switchers aren't more or less
>simple than others) and copied the circuit from some app note.  Both the
>inductor and FET were always hot, usually just about where you couldn't
>touch them for more than a second, even though the whole unit only took
>about 5W.  I was told that when people pointed this out to him he would only
>respond that the circuit was right out of the app note and it therefore
>couldn't be wrong.  He was fired and I was brought in.

As an engineer who has been involved with switching power supplies
for 35 years (they are very different now!) I can only agree. I spend
as much time designing the SM regulators on a PowerPC based CPU board
as I do in the entire PowerPC part, which is what I am doing right now.

One thing that does annoy me somewhat is the lack of decent
simulation models for many switchers. Linear Tech do a good job, but
National, as an example, do a really lousy job. But I end up being
conflicted because all too often the National part is much more
economical but the lT Part has a good model.

There is far more deep theory in SM power supply design than any
other common aspect of modern electronics. I work on everything from
1V @ 1W or less, to 150kV at 100kW every day. So any applicant for a
job in my group that says "oh switchers are simple" doesn't tend to last long!

John

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[John Day-5]

At 02:07 PM 12/12/2008, Herbert Graf wrote:

>On Fri, 2008-12-12 at 09:47 -0800, William "Chops" Westfield wrote:
> > Just out of curiosity:
> >
> > > I'm looking for a hardware engineer to do most of the basic work of
> > > designing class D audio power amplifiers.
> >
> > Hasn't this reached the stage of "pick a class D amp chip and follow
> > the manufacturer recommendations ?
>
>I'd have to agree. Even for the more broad SMPS supply world actually
>designing an SMPS is becomming less and less necessary, in many cases
>just use the online tools to select which chip is best, and follow the
>reference design.
>
>That's not to say that bringup doesn't require skill, and I believe it's
>here that the expertise is most valuable. Getting even a reference SMPS
>design physically working can sometimes be a challenge.

Then don't ever apply for a job as a switch mode power supply designer!

I have a design on the desk right now. Choosing the basic parts alone
for a 24V in CPU PCB based on a PowerPC chip has taken nearly three
days. Now I have to design the regulators, probably close to 10 days
worth of work. But then, as my junior engineer reminded my technician
the other day, I don't design switchers that are trouble. A design
with a new chip can take 15 to 20 pages of calculations and notes.
And the PCB designer who doesn't follow my layout instructions had
better have a good path of communication with his maker, for he will need help.

Oh I have had my failures over the years, but none ever made it into
production. In the twelve months I have been in this job I haven't
missed yet, and generally at this level I end up with 95% plus efficiency.

Class D amplifiers are much the same, and so are motor drives.
Anybody can get a basic reference design working. But it takes a lot
of hard work to get the real thing going well. One reason why class-D
and motor drive designers are highly sought after and well paid.

There is a reason why SMPS groups have things like Dynamic Signal
Analysers, Network Analysers and good high performance oscilloscopes.
Much more valuable than application notes.

John

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[Alan Smith-10]

I just finished up a nice parallel bridge tied load 30W class D amp.  Like switchers, its really all in the layout of the output side.  TI has a really good selection of class D chips, however I used a Cirrus device.


--- On Fri, 12/12/08, Olin Lathrop <olin_piclist@...> wrote:

> From: Olin Lathrop <olin_piclist@...>
> Subject: Re: [BUY] Looking for EE, switching power supp, class D audio
> To: "Microcontroller discussion list - Public." <piclist@...>
> Date: Friday, December 12, 2008, 11:16 AM
> Herbert Graf wrote:
> >> Hasn't this reached the stage of "pick a
> class D amp chip and follow
> >> the manufacturer recommendations ?
> >
> > I'd have to agree. Even for the more broad SMPS
> supply world actually
> > designing an SMPS is becomming less and less
> necessary, in many cases
> > just use the online tools to select which chip is
> best, and follow the
> > reference design.
>
> For some level or performance, cost, efficiency, and board
> space this is
> true, but not for all.
>
>
> ********************************************************************
> Embed Inc, Littleton Massachusetts,
> http://www.embedinc.com/products
> [phone].  Gold level PIC consultants since 2000.
> --
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist

     
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