Searching \ for '[EE] 12 or 24V?' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/index.htm?key=24v
Search entire site for: '12 or 24V?'.

Exact match. Not showing close matches.
PICList Thread
'[EE] 12 or 24V?'
2008\06\25@143333 by Dario Greggio

face picon face
Just asking a... generic question:
I planned to have (as I already did in my previous home) 12 or 24Vcc
around the house to be used for remote device, small actuators and such.

I'll also have 12V (traditional supply - no switching) for audio, using
2x0.50 + 4x0.22 shielded cable.

But, the other one, will go around via CAT5e cable, using a
similar-to-PoE standard, powered via a 2.5A switching supply.
I'm just wondering if it's better 12 or 24V...

The remote devices are PIC16F628 or 18F1320 based... @5V. A linear
regulator with a small dissipator is ok (tested for years @24V).
I just believe that I may never need 24V - it would be most needed in
industrial field, not at home...

But, still, I'm left undecided...

--
Ciao, Dario -- ADPM Synthesis sas -- http://www.adpm.tk

2008\06\25@162205 by alan smith

picon face
PoE is 48V, so you might consider that.  Remember that your going to lose voltage as you push it around, thats a good reason to use 48V and buck it down (or linear..whatever).  I actually used 24VAC not DC in my house.


--- On Wed, 6/25/08, Dario Greggio <spam_OUTadpm.toTakeThisOuTspaminwind.it> wrote:

{Quote hidden}

> --

2008\06\25@163357 by Dario Greggio

face picon face
alan smith wrote:

> PoE is 48V, so you might consider that.  Remember that your going to
> lose voltage as you push it around, thats a good reason to use 48V
> and buck it down (or linear..whatever).  I actually used 24VAC not DC
> in my house.

yep, you're right, this is one of the points I considered. But I don't
expect voltage to lower more then 2-4 volts over my wiring so... 12V
might be ok for the modules... (not for loads indeed).

As for "true" PoE, I'm not using it as is: I have Ethernet on other
cables. This is just for my modules.


--
Ciao, Dario

2008\06\25@180634 by olin piclist

face picon face
Dario Greggio wrote:
> I planned to have (as I already did in my previous home) 12 or 24Vcc
> around the house to be used for remote device, small actuators and
> such.

I would use the highest you can get away with and stay under the regulatory
limit where anyone cares.  I think that is 48V around here, but I haven't
really looked.

If allowed, 48VDC sounds like a good tradeoff.  It is low enough to be safe
in most circumstances, but high enough that you significantly cut down the
size of the conductor for the same power delivered.  Put a small buck
regulator on the front end of all devices.  60V transistors are still small,
cheap, and efficient, so this will be easy to do.  Even a poor buck switcher
will be more efficient than linearly regulating 12V down to 5V.  48V is also
high enough that a diode drop isn't a large fraction, but low enough that
Schottky diodes are still realistic.  80% efficiency should be possible
without doing anything particularly fancy, like synchronous rectification.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2008\06\26@010138 by Xiaofan Chen

face picon face
On 6/26/08, Dario Greggio <.....adpm.toKILLspamspam.....inwind.it> wrote:
> The remote devices are PIC16F628 or 18F1320 based... @5V. A linear
> regulator with a small dissipator is ok (tested for years @24V).
> I just believe that I may never need 24V - it would be most needed in
> industrial field, not at home...

You can use the industrial things at home. ;-)

So 24V is a good choice. Say you want to have some sensors
at home which is quite possible (say infrared opto sensor) ,
most of them will work at 24V (20V-30V or 10-30V typically).

And it already works at your home.

Xiaofan

2008\06\26@010357 by Xiaofan Chen

face picon face
On 6/26/08, Olin Lathrop <EraseMEolin_piclistspam_OUTspamTakeThisOuTembedinc.com> wrote:
> Dario Greggio wrote:
> > I planned to have (as I already did in my previous home) 12 or 24Vcc
> > around the house to be used for remote device, small actuators and
> > such.
>
> I would use the highest you can get away with and stay under the regulatory
> limit where anyone cares.  I think that is 48V around here, but I haven't
> really looked.
>
> If allowed, 48VDC sounds like a good tradeoff.  It is low enough to be safe
> in most circumstances, but high enough that you significantly cut down the
> size of the conductor for the same power delivered.  Put a small buck
> regulator on the front end of all devices.  60V transistors are still small,
> cheap, and efficient, so this will be easy to do.  Even a poor buck switcher
> will be more efficient than linearly regulating 12V down to 5V.  48V is also
> high enough that a diode drop isn't a large fraction, but low enough that
> Schottky diodes are still realistic.  80% efficiency should be possible
> without doing anything particularly fancy, like synchronous rectification.
>

Say if you have a single-stage buck converter, the efficiency from
24V->5V will be better than 48V->5V. 12V-->5V is even better.

Xiaofan

2008\06\26@053401 by Dario Greggio

face picon face
Olin Lathrop wrote:

> I would use the highest you can get away with and stay under the regulatory
> limit where anyone cares.  I think that is 48V around here, but I haven't
> really looked.

Yep, this is one possibility...

> If allowed, 48VDC sounds like a good tradeoff.  It is low enough to be safe
> in most circumstances, but high enough that you significantly cut down the
> size of the conductor for the same power delivered.  Put a small buck

This is true: though I wonder: I'm "always" draining 50mA @5V, so, would
it make any difference?

> regulator on the front end of all devices.  60V transistors are still small,
> cheap, and efficient, so this will be easy to do.  Even a poor buck switcher
> will be more efficient than linearly regulating 12V down to 5V.  48V is also

I agree, but the board are already there with their 7805, which does its
job well enough.

(more in other replies)


But, besides, since I'm not really doing PoE and I may only need 24V for
solenoids or small motors... the 48V seems out of question IMO...

--
Ciao, Dario

2008\06\26@053440 by Dario Greggio

face picon face
Xiaofan Chen wrote:

> You can use the industrial things at home. ;-)

Yep, it *may* happen!

> So 24V is a good choice. Say you want to have some sensors
> at home which is quite possible (say infrared opto sensor) ,
> most of them will work at 24V (20V-30V or 10-30V typically).

I'm actually using NAIS-Matsushita ones, which are almost like big Leds
in size, and 5V powered...

> And it already works at your home.

yep, that's a point...

thank you

--
Ciao, Dario

2008\06\26@053722 by Dario Greggio

face picon face
Xiaofan Chen wrote:

> Say if you have a single-stage buck converter, the efficiency from
> 24V->5V will be better than 48V->5V. 12V-->5V is even better.

As I wrote in reply to Olin, this enforces the 12V solution - especially
since I'm kind of bound to Linear regulators.

But the 24V would possibly give e more "headroom" in case where I had
long cabling and needed some more current...

The good part is that I can change from 12 to 24 almost on the fly, if I
ever need it... since the only hard-soldered part on the "little boards"
is one small relay - used for cases where a "dry contact" is needed.

--
Ciao, Dario

2008\06\26@074140 by olin piclist

face picon face
Xiaofan Chen wrote:
> Say if you have a single-stage buck converter, the efficiency from
> 24V->5V will be better than 48V->5V. 12V-->5V is even better.

Not necessarily.  There is no theoretical basis for your statement, and this
is highly dependent on the circuit.  There are various factors that get both
better and worse as voltage goes up.

For example, one product I designed works from a wall wart that can provide
as low as 20VDC, or POE which is nominally 48VDC.  The circuit itself was
designed to work up to 60V for some margin.  The first stage power supply
takes this input and bucks it down to about 5.5V.  I have measured the power
supply, and efficiency is pretty constant accross the 20V - 60V range.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2008\06\26@093224 by Thomas C. Sefranek

face picon face

-----Original Message-----
From: piclist-bouncesspamspam_OUTmit.edu [@spam@piclist-bouncesKILLspamspammit.edu] On Behalf Of
Xiaofan Chen
Sent: Thursday, June 26, 2008 1:04 AM
To: Microcontroller discussion list - Public.
Subject: Re: [EE] 12 or 24V?

Say if you have a single-stage buck converter, the efficiency from
24V->5V will be better than 48V->5V. 12V-->5V is even better.

Xiaofan

What???

Not in my experience, they all are the same efficiency.

O.K. Remind me what I have forgotten...

Tom

 *
 |  __O    Thomas C. Sefranek  KILLspamWA1RHPKILLspamspamARRL.NET
 |_-\<,_   Amateur Radio Operator: WA1RHP
 (*)/ (*)  Bicycle mobile on 145.41MHz PL74.4

ARRL Instructor, Technical Specialist, VE Contact.
hamradio.cmcorp.com/inventory/Inventory.html
http://www.harvardrepeater.org

2008\06\26@094638 by Xiaofan Chen

face picon face
On Thu, Jun 26, 2008 at 9:32 PM, Thomas C. Sefranek <RemoveMEtcsTakeThisOuTspamcmcorp.com> wrote:
>
> -----Original Message-----
> From: spamBeGonepiclist-bouncesspamBeGonespammit.edu [TakeThisOuTpiclist-bouncesEraseMEspamspam_OUTmit.edu] On Behalf Of
> Xiaofan Chen
> Sent: Thursday, June 26, 2008 1:04 AM
> To: Microcontroller discussion list - Public.
> Subject: Re: [EE] 12 or 24V?
>
> Say if you have a single-stage buck converter, the efficiency from
> 24V->5V will be better than 48V->5V. 12V-->5V is even better.
>
> Xiaofan
>
> What???
>
> Not in my experience, they all are the same efficiency.
>
> O.K. Remind me what I have forgotten...

Typically Buck Converter works better when duty ratio is
between 0.2 to 0.8 (or 0.1 to 0.9). The efficiency will get
worse when the duty ratio is above 0.9 or below 0.1.

Of course this depends on the particular converter used.
I am now testing a 10V-32V --> 5V DC/DC converter
using synchronous buck converter. I am using one of
the best PWM controller available (LTC3835-1) in terms
of size and efficiency (well above 90% at 1A load). The
best efficiency is at 10V and the worst is at 32V.

Xiaofan

2008\06\26@104622 by Vasile Surducan

face picon face
On 6/26/08, Thomas C. Sefranek <RemoveMEtcsspamTakeThisOuTcmcorp.com> wrote:
>
> -----Original Message-----
> From: piclist-bouncesEraseMEspam.....mit.edu [EraseMEpiclist-bouncesspammit.edu] On Behalf Of
> Xiaofan Chen
> Sent: Thursday, June 26, 2008 1:04 AM
> To: Microcontroller discussion list - Public.
> Subject: Re: [EE] 12 or 24V?
>
> Say if you have a single-stage buck converter, the efficiency from
> 24V->5V will be better than 48V->5V. 12V-->5V is even better.

:) :)

Difference between young (unexperienced but enthusiastics) and old
guys can always be found in post like this one...
Vasile

2008\06\26@110228 by Xiaofan Chen

face picon face
On Thu, Jun 26, 2008 at 10:45 PM, Vasile Surducan <RemoveMEpiclist9EraseMEspamEraseMEgmail.com> wrote:
> On 6/26/08, Thomas C. Sefranek <RemoveMEtcsspam_OUTspamKILLspamcmcorp.com> wrote:
>>
>> Say if you have a single-stage buck converter, the efficiency from
>> 24V->5V will be better than 48V->5V. 12V-->5V is even better.
>
> :) :)
>
> Difference between young (unexperienced but enthusiastics) and old
> guys can always be found in post like this one...
> Vasile

I do not understand what you mean here. I am not that old but I
am not that young either.

Xiaofan

2008\06\26@110359 by Xiaofan Chen

face picon face
On Thu, Jun 26, 2008 at 11:02 PM, Xiaofan Chen <RemoveMExiaofancTakeThisOuTspamspamgmail.com> wrote:
> On Thu, Jun 26, 2008 at 10:45 PM, Vasile Surducan <EraseMEpiclist9spamspamspamBeGonegmail.com> wrote:
>> On 6/26/08, Thomas C. Sefranek <RemoveMEtcsKILLspamspamcmcorp.com> wrote:
>>>
>>> Say if you have a single-stage buck converter, the efficiency from
>>> 24V->5V will be better than 48V->5V. 12V-->5V is even better.
>>
>> :) :)
>>
>> Difference between young (unexperienced but enthusiastics) and old
>> guys can always be found in post like this one...
>> Vasile
>
> I do not understand what you mean here. I am not that old but I
> am not that young either.
>

And in terms of the understanding of DC/DC converters, I believe
not many people are better than I.

Xiaofan

2008\06\26@165239 by olin piclist

face picon face
Xiaofan Chen wrote:
> Typically Buck Converter works better when duty ratio is
> between 0.2 to 0.8 (or 0.1 to 0.9). The efficiency will get
> worse when the duty ratio is above 0.9 or below 0.1.

There is nothing in basic physics that says this needs to be true, which is
why it isn't.  This may be true for some types of converters with particular
properties, but to say this broadly applies is just wrong.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2008\06\26@184049 by Xiaofan Chen

face picon face
On Fri, Jun 27, 2008 at 4:54 AM, Olin Lathrop <olin_piclistSTOPspamspamspam_OUTembedinc.com> wrote:
> Xiaofan Chen wrote:
>> Typically Buck Converter works better when duty ratio is
>> between 0.2 to 0.8 (or 0.1 to 0.9). The efficiency will get
>> worse when the duty ratio is above 0.9 or below 0.1.
>
> There is nothing in basic physics that says this needs to be true, which is
> why it isn't.  This may be true for some types of converters with particular
> properties, but to say this broadly applies is just wrong.

There is. I've done theoretical steady state analysis, albeit simplified,
to show that at very low and very high duty ratio, the buck
converter efficiency will suffer. And it is in line with my past
experiences since I have developed two universal input sensor
(20V-240V DC and AC) using a buck converter which converts
the high voltage to

And quite some PWM controllers actually limit the minimum
and maximum duty ratio.

The value of 0.1-0.9 is a ball-park value.

The following article
http://www.powermanagementdesignline.com/howto/207500488

"If you have a 24-volt input and 1.2-volt output, for example,
you need a duty ratio of 0.05. But it's not optimized for
efficiency or performance. And in the common buck converter,
a very low duty ratio often isn't easily achieved."

Xiaofan

2008\06\26@184551 by Xiaofan Chen

face picon face
On Thu, Jun 26, 2008 at 7:43 PM, Olin Lathrop <spamBeGoneolin_piclistSTOPspamspamEraseMEembedinc.com> wrote:
> Not necessarily.  There is no theoretical basis for your statement, and this
> is highly dependent on the circuit.  There are various factors that get both
> better and worse as voltage goes up.
>
> For example, one product I designed works from a wall wart that can provide
> as low as 20VDC, or POE which is nominally 48VDC.  The circuit itself was
> designed to work up to 60V for some margin.  The first stage power supply
> takes this input and bucks it down to about 5.5V.  I have measured the power
> supply, and efficiency is pretty constant accross the 20V - 60V range.
>

Lower the output voltage to say 3V and you will know the effect of
low duty ratio. Or increase the input voltage to say 100V.

Xiaofan

2008\06\26@210537 by Xiaofan Chen

face picon face
On 6/27/08, Xiaofan Chen <KILLspamxiaofancspamBeGonespamgmail.com> wrote:
> On Fri, Jun 27, 2008 at 4:54 AM, Olin Lathrop <EraseMEolin_piclistspamEraseMEembedinc.com> wrote:
> > There is nothing in basic physics that says this needs to be true, which is
> > why it isn't.  This may be true for some types of converters with particular
> > properties, but to say this broadly applies is just wrong.
>
> There is. I've done theoretical steady state analysis, albeit simplified,
> to show that at very low and very high duty ratio, the buck
> converter efficiency will suffer.

More theoretical analysis here:
scholar.lib.vt.edu/theses/available/etd-03092002-004940/
Read Chapter 2 about the low duty ratio's effect to the multi-phase
buck converter. It applies to single phase synchronous buck
converter as well.

The above assertion is about normal single stage
buck converter without a transformer or coupled
inductor. If a transformer is involved (which changes
the effective duty ratio), high input  voltage can actually be
an advantage.


Xiaofan

2008\06\27@085117 by olin piclist

face picon face
Xiaofan Chen wrote:
>> There is nothing in basic physics that says this needs to be true,
>> which is why it isn't.  This may be true for some types of
>> converters with particular properties, but to say this broadly
>> applies is just wrong.
>
> There is. I've done theoretical steady state analysis, albeit
> simplified,
> to show that at very low and very high duty ratio, the buck
> converter efficiency will suffer. And it is in line with my past
> experiences since I have developed two universal input sensor
> (20V-240V DC and AC) using a buck converter which converts
> the high voltage to
>
> And quite some PWM controllers actually limit the minimum
> and maximum duty ratio.

Let's look at where energy gets wasted in a simple buck converter.  The
input voltage is connected thru a switch to the inductor and a diode from
ground.  the other end of the inductor goes to the output voltage.  The main
losses are due to the voltage accross the switch when on, the I^2*R loss in
the inductor, and the voltage drop accross the diode when it is on.  There
is also current loss thru the switch and the diode during its reverse
recovery time if the converter is run in continuous mode.

Let's start by analysing the ideal zero-cross mode case where a new pulse is
started immediately after the previous one has finished.  The inductor
current is therefore a sawtooth, with the rising edge slope proportional to
the input minus output voltage and the falling slope proportional to the
output voltage (plus the diode drop).  The fact that there is a high ratio
between the two slopes is of itself not a cause for inefficiency.  As the
input voltage is changed with everything else constant, the only difference
is the leading slope of the inductor current.  The average and peak and RMS
inductor currents stay the same, so the IIR losses in the inductor stay the
same.  Since the diode only conducts during the falling slope, the loss due
to its forward voltage stays the same.

The losses in the switch do vary as a function of the input voltage.  If the
switch is ideal except for a fixed voltage drop, then the losses actually go
down as input voltage is increased.  If the switch is ideal except for a
fixed on resistance, then the losses also go down with higher input voltage
although the equation is a bit different.

So looking at the first approximation case, higher input voltage would seem
to be better.  The approximation breaks down as real world properties of
available switches deviate from ideal.  The gain of bipolar transistors goes
down as they are designed to withstand more voltage.  The on resistance of
FETs goes up as they are designed to withstand more voltage.  To reduce
ripple and to allow for smaller and cheaper inductors, you have to increase
switching frequency.  Switching losses start to dominate as the switching
transition time because a significant fraction of the switch on time per
pulse.  Higher voltages require shorter pulses with everything else held
constant for some configurations.  I think this probably your main
objection.

However, as with most design issues, you can design for some tradeoffs at
the expense of others.  One obvious solution is to enforce a minimum pulse
size.  This is in fact what I often do.  That means some efficiency is
sacrificed at low currents.  More frequent shorter pulses would have less
IIR loss.  But with minimum pulse sizes you also get tolerance to wider
input voltages and can access some of the benefits of higher input voltages.

I have no doubt that you have experience with power supplies that are less
efficient at higher input voltages.  Design tradeoffs can certainly be made
where that would be the case.  But you have to stop and realize this general
tradeoff is not a universal rule, but rather a characteristic of specific
(perhaps even common) designs.

The main criteria to allow for efficient switching power supply design is
predictable input and output voltages and currents.  If you know those, you
can design around the input to output voltage ratio.  The more latitude you
have to allow in the input voltage, the more some other parameters will be
compromised.  Something will give, like a larger inductor, more ripple
voltage, lower switching frequency, but it doesn't inherently need to be
efficiency.

As I said before, the power supply I designed for a particular unit was
designed to produce a roughly regulated 5.6V from 20-60V input.  Final
efficiency was pretty flat accross the full input voltage range.  My supply
probably had more ripple than the ones you are thinking of, but that was
fine for what it needed to be.  In other applications tight output voltage
control and low ripple may be more important, and then efficiency might vary
accross a 3:1 input voltage range.  It depends on what is important in each
case.

By the way, this particular supply achieved reasonably constant effiency
accross the 3:1 input voltage range and over 10:1 input to output voltage
ratio by using a pulse on demand system in discontinuous mode.  The
switching transitions were guaranteed to be negligeable in all cases
compared to the switch on time.  The algorithm did not use a fixed pulse
size, but adjusted this "slowly" to avoid large pulses with large times
between them, but always kept to a certain minimum pulse size regardless.
This kind of control algorithm is one of the nice things you can do with a
programmable processor that is difficult to achieve with analog systems.  In
this case the controller was a PIC 10F204.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2008\06\27@085449 by olin piclist

face picon face
Xiaofan Chen wrote:
> Lower the output voltage to say 3V and you will know the effect of
> low duty ratio. Or increase the input voltage to say 100V.

I can't.  This particular supply was designed to work with 20-60V input.
You can't expect it to work outside of its design range.

The point is that efficiency does not inherently need to suffer as input
voltages go up.  Note I'm talking about "reasonable" input voltages where
suitable transistors are available for the switch.  Things get different
above a few 100 volts because available switches become less and less ideal
and driving them becomes tricky too.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2008\06\27@085750 by olin piclist

face picon face
Xiaofan Chen wrote:
> More theoretical analysis here:
> scholar.lib.vt.edu/theses/available/etd-03092002-004940/
> Read Chapter 2 about the low duty ratio's effect to the multi-phase
> buck converter. It applies to single phase synchronous buck
> converter as well.

That's 52 page PDF I don't have time to read now.  If you have valid points,
you should be able to summarize them in a few paragraphs.

> If a transformer is involved (which changes
> the effective duty ratio), high input  voltage can actually be
> an advantage.

I was assuming we were discussing simple DC coupled buck converters with a
switch, inductor, and diode.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2008\06\27@095741 by Xiaofan Chen

face picon face
On Fri, Jun 27, 2008 at 8:53 PM, Olin Lathrop <@spam@olin_piclist@spam@spamspam_OUTembedinc.com> wrote:
> Switching losses start to dominate as the switching
> transition time because a significant fraction of the switch on time per
> pulse.  Higher voltages require shorter pulses with everything else held
> constant for some configurations.  I think this probably your main
> objection.

Firstly thanks for putting efforts so that others can understand. Some
people here clearly do not under even the basics of buck converter.

Modern MOSFETs are pretty good and have low Rds-on and tends to
have higher switching frequency, and switching losses are often the
dominate. So yes this was what I mind. But it is more than this.
Even with more traditional lower switching frequency buck converter
(MOSFET + free-wheeling diode), where conduction loss is the dominating
factor, lower duty ratio is still not desired as the free-wheeling diode will
conduct most of the time and thus have higher loss due to the diode
voltage drop. That is why synchronous buck converter becomes more
and more popular in many applications.

> I have no doubt that you have experience with power supplies that are less
> efficient at higher input voltages.  Design tradeoffs can certainly be made
> where that would be the case.  But you have to stop and realize this general
> tradeoff is not a universal rule, but rather a characteristic of specific
> (perhaps even common) designs.

I would say common design is what I had in mind. I would not say it is
a universal rule but it is kind of a common sense within the filed of
power electronics that you do not want the duty cycle to be as low
as 0.05.

Regards,
Xiaofan

2008\06\27@103805 by olin piclist

face picon face
Xiaofan Chen wrote:
> Even with more traditional lower switching frequency buck converter
> (MOSFET + free-wheeling diode), where conduction loss is the
> dominating
> factor, lower duty ratio is still not desired as the free-wheeling
> diode will conduct most of the time and thus have higher loss due to
> the diode
> voltage drop.

That's a good point I screwed up in my previous message.  In a buck
converter, part of the output current comes directly from the input and some
from ground thru the diode.  The ratio depends on the input to output
voltage ratio, with high input to output voltage ratio causing a larger
portion of the output current to pass thru the diode and its voltage drop.
At a low output voltage like 5.6V, even a Schottky can waste 5% of the power
during the current from ground part of the pulse.  If you make sure
switching times are short compared to the pulse width, the high side
switching losses will decrease with higher voltage.  In the end you can
achieve are roughly constant efficiency as I did over a reasonable range.
Since at my lowest input voltage the ratio was already nearly 4:1, the diode
was conducting for about 3/4 of the output current already, so adding the
other 25% didn't make that much of a difference.

> That is why synchronous buck converter becomes more
> and more popular in many applications.

Absolutely, especially with low output voltages.

However let's keep in perspective the original question was what voltage
Dario should bus around his house to power a few distributed devices.
Simple buck regulators that are good enough can be easily designed with 12,
24, or 48 volts input.  I was advocating the higher voltage to reduce IIR
losses in the cable and maximize the amount of power that can be transmitted
for the same size cable.  Over time he is likely to add more and more
devices, so designing now for more power capacity sounds like a good idea.
I envision a 48V off the shelf commercial power supply in the basement
powering the system all the time, then the modules bucking that to 5.6V with
a 5V LDO post regulator.  We may disagree on whether 48V will be less
efficient to use than 24 or 12 volts, but in either case a few percent
difference in the modules isn't really the issue, and would probably be more
than offset by the cable losses anyway.  If he uses off the shelf CAT5
cable, then it will have a maximum current carrying capacity.  At 48V that
same cable will be able to deliver twice the power to the distributed
collection of modules than at 24V.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2008\06\27@110028 by Xiaofan Chen

face picon face
On Fri, Jun 27, 2008 at 10:40 PM, Olin Lathrop
<spamBeGoneolin_piclistspamKILLspamembedinc.com> wrote:
> However let's keep in perspective the original question was what voltage
> Dario should bus around his house to power a few distributed devices.
> Simple buck regulators that are good enough can be easily designed with 12,
> 24, or 48 volts input.  I was advocating the higher voltage to reduce IIR
> losses in the cable and maximize the amount of power that can be transmitted
> for the same size cable.  Over time he is likely to add more and more
> devices, so designing now for more power capacity sounds like a good idea.
> I envision a 48V off the shelf commercial power supply in the basement
> powering the system all the time, then the modules bucking that to 5.6V with
> a 5V LDO post regulator.  We may disagree on whether 48V will be less
> efficient to use than 24 or 12 volts, but in either case a few percent
> difference in the modules isn't really the issue, and would probably be more
> than offset by the cable losses anyway.  If he uses off the shelf CAT5
> cable, then it will have a maximum current carrying capacity.  At 48V that
> same cable will be able to deliver twice the power to the distributed
> collection of modules than at 24V.
>

In terms of distributed power, yes I agree 48V is better. But my original
perspective is that 24V is more popular for automation (including home
automation).

Whether 48V is a safe voltage is a moot point as well. Typically we
only consider <36V as safe.


Xiaofan

2008\06\27@170959 by Dario Greggio

face picon face
Olin Lathrop wrote:

> However let's keep in perspective the original question was what voltage
> Dario should bus around his house to power a few distributed devices.

Hi guys, I'm glad this lead to such an interesting discussion between
you :))

> Simple buck regulators that are good enough can be easily designed with 12,
> 24, or 48 volts input.  I was advocating the higher voltage to reduce [...]
> Over time he is likely to add more and more
> devices, so designing now for more power capacity sounds like a good idea.

indeed, true.
Only thing, I find it hard to put there the buck converters at the
moment. But it may come true later.

> [...]We may disagree on whether 48V will be less
> efficient to use than 24 or 12 volts, but in either case a few percent
> difference in the modules isn't really the issue, and would probably be more
> than offset by the cable losses anyway.  If he uses off the shelf CAT5
> cable, then it will have a maximum current carrying capacity.  At 48V that
> same cable will be able to deliver twice the power to the distributed
> collection of modules than at 24V.

Yep.
At the moment I'm considering 24V as a good intermediate value :)

--
Ciao, Dario

2008\06\27@175108 by olin piclist

face picon face
Dario Greggio wrote:
> Yep.
> At the moment I'm considering 24V as a good intermediate value :)

You should go into politics ;-)

********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2008\06\27@180441 by Dario Greggio

face picon face
Olin Lathrop wrote:

> Dario Greggio wrote:
>
>>At the moment I'm considering 24V as a good intermediate value :)
>
> You should go into politics ;-)

:)
seriously, I have to ask if 48V is "safe" in Italy.
And, moreover, that can't definitely work with my current LDOs in place.


--
Ciao, Dario

2008\06\27@204645 by Cedric Chang

flavicon
face
>
> On Jun 27, 2008, at 4:04 PM, Dario Greggio wrote:
>
> Olin Lathrop wrote:
>
>> Dario Greggio wrote:
>>
>>> At the moment I'm considering 24V as a good intermediate value :)
>>
>> You should go into politics ;-)
>
> :)
> seriously, I have to ask if 48V is "safe" in Italy.
> And, moreover, that can't definitely work with my current LDOs in  
> place.

What is safe in Italy ? ( Different physics than the USA  
obviously )   Would 30V be safe ? 36V ?  I say crank it up to  
whatever the official voltage for Italy is.  In the USA I believe it  
is 48V.
Strangely, the telephone ring voltage in the USA is specified to be  
88V peak.
cc

2008\06\28@042622 by KPL

picon face
>
> :)
> seriously, I have to ask if 48V is "safe" in Italy.
> And, moreover, that can't definitely work with my current LDOs in place.
>


Is it really that difficult (space constraints?) to add an additional
tiny board with switcher that drops those 48V to the level that Your
boards are designed for? Your LDO will even filter away the excess
ripple so switcher can be very simple.


--
KPL

2008\06\28@052401 by Nicola Perotto

picon face
Not safe but "safe" !!!
It is a problem of bureaucracy not of physics ...


Cedric Chang wrote:
{Quote hidden}

2008\06\28@053146 by Dario Greggio

face picon face
Nicola Perotto wrote:

> Not safe but "safe" !!!
> It is a problem of bureaucracy not of physics ...

thank you Nicola :)
by the way, I still have to ask to any experts...

2008\06\28@055801 by Ruben Jönsson

flavicon
face

> seriously, I have to ask if 48V is "safe" in Italy.
> And, moreover, that can't definitely work with my current LDOs in place.
>
>

According to EN 61010 - Safety requirements for electrical equipment for
measurement, control and laboratory use, the permissible limits for accessible
parts are 33V rms and 46.7V peak or 70VDC. For equipment rated for wet
locations the voltage levels are 16Vrms and 22.6V peak or 35VDC.

And here is a question about that: Say I have a pulsed DC between 0V and +50V,
1 second on and 1 second off where 0V is tied to earth. Is that still DC or do
I get outside the limits for 46.7V peak. Or does it count as an AC centered
around +25V (from earth) with an rms of 25V? Would it make a difference if it
is isolated from earth or not?

/Ruben
==============================
Ruben Jönsson
AB Liros Electronic
Box 9124, 200 39 Malmö, Sweden
TEL INT +46 40142078
FAX INT +46 40947388
.....rubenspam_OUTspampp.sbbs.se
==============================

2008\06\28@084938 by Dario Greggio

face picon face
KPL wrote:

> Is it really that difficult (space constraints?) to add an additional
> tiny board with switcher that drops those 48V to the level that Your
> boards are designed for? Your LDO will even filter away the excess
> ripple so switcher can be very simple.

I'm posting 2 pictures to show the case.
As you can see, I actually can't do that right now (and next install as
well, to where I'm moving soon).

In theory, removing the 7805 DPAK one could fit a buck converter with
just a little increase in space - but it might be next version.

The "larger box" hosts a board with IR recevier, 2 220V output with
Triacs, and 3 inputs.
The "smaller box" only has one 220V output and one button.

--
Ciao, Dario






2008\06\28@092831 by olin piclist

face picon face
Dario Greggio wrote:
> seriously, I have to ask if 48V is "safe" in Italy.
> And, moreover, that can't definitely work with my current LDOs in
> place.

Even 24V would be pusing it with a linear regulator.  Only 53mA is 1W
dissipation in a linear regulator dropping 24V to 5V.  If you're going to
use linear regulators anyway, then higher voltage will only make things
worse.  You don't get the extra power carrying capacity of the wire and burn
up a lot more power in heat in the modules.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2008\06\28@093131 by olin piclist

face picon face
Cedric Chang wrote:
> What is safe in Italy ? ( Different physics than the USA
> obviously )

Maybe Italians are less resistive.  Must be the olive oil.  ;-)

********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2008\06\28@093740 by Dario Greggio

face picon face
Olin Lathrop wrote:

> Even 24V would be pusing it with a linear regulator.  Only 53mA is 1W
> dissipation in a linear regulator dropping 24V to 5V.  If you're going to
> use linear regulators anyway, then higher voltage will only make things
> worse.  You don't get the extra power carrying capacity of the wire and burn
> up a lot more power in heat in the modules.

Yep, this is the point: my compromise, with current parts, between the
LDO (and cable) power waste, and the possibility to power 24V devices
here and there.

--
Ciao, Dario

2008\06\28@094028 by Dario Greggio

face picon face
Olin Lathrop wrote:

> Maybe Italians are less resistive.  Must be the olive oil.  ;-)

:)
Law is... "fluid" in here, flexible, you know... :-(

--
Ciao, Dario

More... (looser matching)
- Last day of these posts
- In 2008 , 2009 only
- Today
- New search...