Re: PWM in a switching power supply
- From: w_tom <w_tom1@xxxxxxxxxxx>
- Date: Tue, 31 May 2005 23:48:50 -0400
Somewhere was an 85(?) page introduction (from linear.com)
to switching power supply design. Up front was a flow chart
that asked if one wants to design a supply? The Yes path lead
to a message that asked, "Are you Nuts?" Power supply design
is complex. As demonstrated here, one must have knowledge of
filters, feedback systems, principles of power systems, EMC,
UL approval, FCC regulations, etc. A beginner must first
decide how much will be learn before his eyes disappear into
the back of his head.
If consumer pushed bean counters to reduce costs, then Honda
and Toyota would not be dominant and growing car companies.
Bean counters typically increase product costs - at least in
the long term. It explains why GM has so many problems. Cost
controls increase costs. To reduce costs, obtain more
customers, create new markets, increase market share, create
jobs, create wealth, increase product efficiency, etc... all
require the most important thing - innovation. The US is a
miser as are most every other nation. To sell in the US or
anywhere else, the power supply manufacturer must innovate -
not cost control. Meanwhile the US does have standards that
some other nations do not have - for power supply performance,
reliability, safety, emissions, and .... Europe has even
tougher standards.
Most supplies, to be profitable, must be designed to operate
anywhere in the world - either as a universal supply or with
different options for different regions. Just another example
of innovation; the alternative being bankruptcy. Just another
reason why (outside of niche markets), the power supply
designs must meet fairly universal world standards.
Tell us about harmonics? Do we solve this problem with
filters, or what else? Will a power supply create too much
harmonics AND will it operate when line harmonics are high?
I recall the Intel spec that even demands output transient
response - another factor in a feedback control system
design. Power supply design is not about costs. It is about
innovation - where costs are only one small part of a
profitable design. The only way to cut costs and remain
competitive - innovation.
A large market for inferior supplies exists that create
problems such as computer system damage and intermittent
failures. All power supply outputs must even be shorted and
still not damage the supply. This too has been defacto
standard for many decades.
We have demonstrated how much is basic information on power
supplies. IOW, "your nuts" in that flow chart should be
appreciated. 85(?) pages in that introduction paper
demonstrates how complex a switching power supply really is
and why a properly constructed supply selling for only $65
retail is a marvel of free market economics.
However when purchasing a $40 retail supply, then ask what
critical functions were forgotten to sell that supply only on
price. Yes, some sell power supplies only using cost
controls.
Joel Kolstad wrote:
> Hi W_Tom,
> "w_tom" <w_tom1@xxxxxxxxxxx> wrote in message
> news:42979DF8.390CDDFA@xxxxxxxxxxxxxx
> > That's correct and consistent with what I had posted.
>
> Hmm... if you say so. That's sure not how I read your post.
>
> > As noted
> > earlier, this can cause increased energy dissipation in the
> > transformer and elsewhere.
>
> Yes, certainly true, but not really relevant to what a beginner needs to know.
>
> > An unloaded power supply must not be damaged by no load.
>
> For a bench supply or even a PC power supply, I'm tempted to agree with you.
> For embedded applications in cut-throat markets (TVs are a very good example),
> it's hard to ignore the cost savings that can be achieved by not bothering to
> make your power supply unconditionally stable when you 'know' there will
> always be a minimum load around.
>
> > Any power supply that is damaged by a no load condition is
> > typical of something bought by a bean counter - the enemy of
> > innovators, responsible manufacturers, and those educated in
> > computer electronics.
>
> It's the consumer who pushes the bean counters to skimp on parts count and/or
> quality. Although the US is a wealthy country that can readily afford to pay
> a couple bucks extra for a better computer power supply, this isn't true in
> all parts of the world (e.g., China). It's not the kind of engineering work I
> want to do, but I can see the justification for designing these really awful
> PC power supplies that cost literally no more than $10 but can readily blow-up
> if you look at them crosseyed.
>
> > But a power supply
> > designer better damn well understand the principles of filter
> > design.
>
> Mnay people get along just fine with being able to analyze single section
> filters (both the main L-C 'power' filter and something cheesy like an R-C
> feedback loop filter). Now, you may consider than the "principles of filter
> design," but personally I would say that someone well versed in such
> "principles" is more like to be able to spout off about Chebychev filters,
> group delay, Butterworth pole positions -- that sort of thing -- than just
> what simple LC and RC filters do. (I realize many power supplies do have
> "fancy" filters in the feedback path, I'm just saying plenty of them don't and
> I don't think you really need to know that much about filter design to make a
> workable switcher.)
>
> ---Joel
.
- References:
- Re: PWM in a switching power supply
- From: Joel Kolstad
- Re: PWM in a switching power supply
- Prev by Date: Re: Any problem parallel traces on both sides of board carrying same signal?
- Next by Date: Re: Random ON/OFF Timer Circuit
- Previous by thread: Re: PWM in a switching power supply
- Next by thread: Re: PWM in a switching power supply
- Index(es):
Relevant Pages
|
