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'[EE] wanted: 18V linear regulator for more than 1A'
2008\10\20@141755 by alan smith

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Yes..I know a switcher will do the job, but there are reasons for using a linear in this application (low noise, RF, AF).  And its not my design, I'm just trying to circumvent the power problem before it becomes an issue.

The good ol 7818 and such in the TO-220 package are only rated to 1A, but I need closer to 2A.  Anyone know of a device, doesnt have to be that package, that can go upwards of that current load?

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2008\10\20@142542 by Byron Jeff

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On Mon, Oct 20, 2008 at 02:17:34PM -0400, alan smith wrote:
>

> Yes..I know a switcher will do the job, but there are reasons for using a
> linear in this application (low noise, RF, AF).  And its not my design,
> I'm just trying to circumvent the power problem before it becomes an
> issue.

>
> The good ol 7818 and such in the TO-220 package are only rated to 1A, but
> I need closer to 2A.  Anyone know of a device, doesnt have to be that
> package, that can go upwards of that current load?

Get a LM317 in the TO-3 metal can. Only requires two extra resistors to set
the voltage and is rated up to 5A with heatsinking.

BAJ

2008\10\20@144327 by olin piclist

face picon face
alan smith wrote:
> Yes..I know a switcher will do the job, but there are reasons for
> using a linear in this application (low noise, RF, AF).  And its not
> my design, I'm just trying to circumvent the power problem before it
> becomes an issue.
>
> The good ol 7818 and such in the TO-220 package are only rated to 1A,
> but I need closer to 2A.  Anyone know of a device, doesnt have to be
> that package, that can go upwards of that current load?

What voltage is it starting with.  Power dissipation may be more of a issue
than current.

Maybe a switching preregulator followed by a linear if you really need
quiet.


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

2008\10\20@145656 by alan smith

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Ahh...your right.  I looked at one datasheet but it must have been the DPAK or TO220, not the TO3 since it was stating 1A on those.  Yep, two extra resistors isnt a deal breaker.


--- On Mon, 10/20/08, Byron Jeff <spam_OUTbyronjeffTakeThisOuTspamclayton.edu> wrote:

{Quote hidden}

> --

2008\10\20@151704 by alan smith

picon face
Starting voltage is 24VDC


--- On Mon, 10/20/08, Olin Lathrop <.....olin_piclistKILLspamspam.....embedinc.com> wrote:

{Quote hidden}

> --

2008\10\20@153359 by Wouter van Ooijen

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> The good ol 7818 and such in the TO-220 package are only rated to 1A, but I need closer to 2A.  Anyone know of a device, doesnt have to be that package, that can go upwards of that current load?

LM338K?


--

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu

2008\10\20@160249 by olin piclist

face picon face
> Starting voltage is 24VDC

Ouch.  That's a 6V drop, so you'll have to dissipate 12W at your desired 2A
out.

That's a lot of heat.  It really sounds like a switcher, or if necessary a
switching preregulator would be a good idea.  That will likely be smaller
and quite possibly cheaper than whatever you end up with to deal with 12W of
heat.


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

2008\10\20@160354 by Steve Smith

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338K That's the very one I came up with 5A on a 1.1c/w sink 2A I think
should be LM317HVK or similar

Steve

{Original Message removed}

2008\10\20@181021 by Grant Brown

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MIC29752BWT from Micrel

Rated at 7.5 amps.

Grant

Byron Jeff wrote:
{Quote hidden}

--
Kind Regards
Grant Brown

SiteDoc Pty Ltd
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http://www.sitedoc.com.au
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2008\10\20@215309 by Justin Richards

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When detecting very small rf signals is it possible a switching
pre-regulator will present a electrically noisy environment (all those
nasty harmonics) or can they be *completely* screened or perhaps
remotely located to eliminate the noise problem.  If remotely located,
what would be a typical distance.

I ask as I have seen a receiver setup where all the psu's are linear,
not a switching mode power supply anywhere in sight. I thought it
would have been much cheaper to go with switch modes but the designers
chose the expensive option. (expensive in my calculations)

On a related issue,  I would guess that psu's in sensitive test
equipment like spectrum and network analysers would only use linear
psu's.

So my question is can switch mode power supplies be used in
electrically sensitive environments.  Can quiet switchers be produced
or effectively shielded.

Cheers Justin

On Tue, Oct 21, 2008 at 2:43 AM, Olin Lathrop <@spam@olin_piclistKILLspamspamembedinc.com> wrote:
{Quote hidden}

> -

2008\10\20@224622 by Christian Weagle

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Justin Richards wrote:
> So my question is can switch mode power supplies be used in
> electrically sensitive environments.  Can quiet switchers be produced
> or effectively shielded.

Well, low-noise is doable.  As for shielding - mu-metal is always an option.

See Jim William's app note (from Linear Tech) on this subject:

<www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1003,C1040,C1130,P1535,D4159>

2008\10\21@021541 by Justin Richards

face picon face
Thanks Christian,

some of the language of the APP note is a little out there for me but
I figure the solution is *simply* :-

drive a centre tapped inductor with currents that are *tending* to
resemble a sine wave rather than a harsh square wave by slowing the
switching transitions resulting in an tradeoff in efficiency.

On Tue, Oct 21, 2008 at 10:45 AM, Christian Weagle <KILLspamcweagleKILLspamspami9t.net> wrote:
> Justin Richards wrote:
>> So my question is can switch mode power supplies be used in
>> electrically sensitive environments.  Can quiet switchers be produced
>> or effectively shielded.
>
> Well, low-noise is doable.  As for shielding - mu-metal is always an option.
>
> See Jim William's app note (from Linear Tech) on this subject:
>
> <www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1003,C1040,C1130,P1535,D4159>
> -

2008\10\21@064402 by olin piclist

face picon face
Justin Richards wrote:
> When detecting very small rf signals is it possible a switching
> pre-regulator will present a electrically noisy environment (all those
> nasty harmonics) or can they be *completely* screened or perhaps
> remotely located to eliminate the noise problem.

Switchers do have transients, but I've found usually aren't as bad for RF in
the few 100MHz range as switching digital signals.  Good grounding makes a
far bigger difference.


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

2008\10\21@121710 by Peter

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Olin Lathrop <olin_piclist <at> embedinc.com> writes:

> > Starting voltage is 24VDC
>
> Ouch.  That's a 6V drop, so you'll have to dissipate 12W at your desired 2A
> out.
>
> That's a lot of heat.  It really sounds like a switcher, or if necessary a
> switching preregulator would be a good idea.  That will likely be smaller
> and quite possibly cheaper than whatever you end up with to deal with 12W of
> heat.

Dropping 6V out of 24 on a linear regulator at 2A is not 'a lot of heat'. 12W out
of the total 48 that device will be consuming means 75% efficiency for a linear
regulator. It all depends on what can be put in his box and what the overall
efficiency is supposed to be. e.g. using a switcher will improve the overall
efficiency by only at most 25% (more likely by 10-18%). If the larger part of
the consumed power is dissipated in the box already, that won't be justifiable.
On the
other hand, if it is not ...

Peter


2008\10\21@161405 by olin piclist

face picon face
Peter wrote:
> Dropping 6V out of 24 on a linear regulator at 2A is not 'a lot of
> heat'.

12W is going to require a heatsink.  I don't think there is any off the
shelf linearl regulator that can dissipate 12W in just ambient air and not
fry itself, or shut down first.

> 12W out of the total 48 that device will be consuming means
> 75% efficiency for a linear regulator.

Which only matters if the 36W the load uses is in the same box.  I don't
remember the OP stating that one way or another.  It may also not be easy to
piggyback the power supply heat removal on the load heat removal mechanism.


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

2008\10\21@162810 by Funny NYPD

picon face
why not use the SMPS+LDO, it will balance everything.

Funny N.
Au Group Electronics, http://www.AuElectronics.com



{Original Message removed}

2008\10\22@103251 by alan smith

picon face
cost.  Linears are cheap, and they want cheap at the expense of wasted power.  Sometimes its hard to convince the bean counters


--- On Tue, 10/21/08, Funny NYPD <RemoveMEfunnynypdTakeThisOuTspamyahoo.com> wrote:

{Quote hidden}

> {Original Message removed}

2008\10\22@111719 by alan smith

picon face
The load is in the same box, and heatsinks are not a problem, we use them on other products.

I agree that a switcher as a pre-regulator is the best way to go, and if I can get them to at least give me a method of putting on it after, even a demo board unit, to prove out noise issues (or lack there of) then it gives me another avenue to persue.


--- On Tue, 10/21/08, Olin Lathrop <RemoveMEolin_piclistspamTakeThisOuTembedinc.com> wrote:

{Quote hidden}

> --

2008\10\22@174657 by olin piclist

face picon face
alan smith wrote:
> cost.  Linears are cheap, and they want cheap at the expense of
> wasted power.  Sometimes its hard to convince the bean counters

If you had posted this following whatever it is you are replying to, I might
have had more to add.  A little trimming and typing your code in sensible
places goes a long way towards readability.


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

2008\10\22@191300 by Grant Brown

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face
Hi Alan,

The Micrel family of linear voltage regulators will do you job with no
issues. You also get a very handy enable input with them.

http://www.micrel.com

MIC29303BT - Adj 1.25Vdc to 26Vdc @ 3.0 amps  T-220-5 package

MIC29503BT - Adj 1.25Vdc to 26Vdc @ 5.0 amps T-220-5 package

MIC29752BWT - Adj 1.25Vdc to 26Vdc @ 7.5 amps TO-247-5 package

Kind Regards
Grant Brown


Olin Lathrop wrote:
{Quote hidden}

--
Kind Regards
Grant Brown

SiteDoc Pty Ltd
mob: 0412 926 995
http://www.sitedoc.com.au
__________________________________________________________________________________________________________
This email message together with any attachments is intended only for the addressee(s) and contains information that may be confidential and/or copyright.  If you are not the intended recipient, please notify the sender by reply email (or telephone SiteDoc Pty Ltd on +61 2 42291185) and immediately delete this email together with any attachments from your computer. If you are the intended recipient, you must not copy, disclose, reproduce or distribute this communication together with any attachments without the authority of SiteDoc Proprietary Limited. No representation is made that this email or any attachments are free of viruses. Virus scanning is recommended and is the responsibility of the recipient. Unless specifically stated by the sender as the views of SiteDoc Proprietary Limited, any views expressed in this message are those of the individual sender, and no responsibility will be borne by SiteDoc Proprietary Limited for its content or outcomes.

2008\10\22@203419 by Christian Weagle

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Justin Richards wrote:
> Thanks Christian,
>
> some of the language of the APP note is a little out there for me but
> I figure the solution is *simply* :-
>
>  drive a centre tapped inductor with currents that are *tending* to
> resemble a sine wave rather than a harsh square wave by slowing the
> switching transitions resulting in an tradeoff in efficiency.

Right, the point is to not have discontinuous current, and to also have
a fast feedback loop to try to actively deal with spikes.


'[EE] wanted: 18V linear regulator for more than 1A'
2008\11\02@221626 by Sean Breheny
face picon face
As a hobby project I have slowly been building a high-performance HF
receiver over the last few years. I originally used a switching power
supply in it. Granted, I'm only slightly beyond newbie when it comes
to switching power supplies, but I have to say that I found it
impossible to keep the harmonics from the switcher from making it into
the receiver. I tried shielding and massive filtering on the input and
output leads to no real avail. I did not try magnetic shielding,
however the physical separation between the switcher and the rest of
the receiver was such that I would find it hard to believe that there
could be direct magnetic coupling.

I'm sure that it is possible to use switchers in receivers but I think
that lots of effort would be required. I am not surprised if switchers
are rare in receivers.

Spectrum analyzers and scopes, on the other hand, are not nearly as
sensitive, typically, as a receiver. I would think that they DO
include switchers.

Sean


On Mon, Oct 20, 2008 at 8:53 PM, Justin Richards
<RemoveMEjustin.richardsEraseMEspamEraseMEgmail.com> wrote:
{Quote hidden}

>> --

2008\11\03@003811 by Nate Duehr

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On Nov 2, 2008, at 8:16 PM, Sean Breheny wrote:

> As a hobby project I have slowly been building a high-performance HF
> receiver over the last few years. I originally used a switching power
> supply in it. Granted, I'm only slightly beyond newbie when it comes
> to switching power supplies, but I have to say that I found it
> impossible to keep the harmonics from the switcher from making it into
> the receiver. I tried shielding and massive filtering on the input and
> output leads to no real avail. I did not try magnetic shielding,
> however the physical separation between the switcher and the rest of
> the receiver was such that I would find it hard to believe that there
> could be direct magnetic coupling.

Some of the modern "radio grade" switchers provide user controls to  
move the harmonics around by modifying the switcher's frequency, etc.

If you're stuck with a switcher, you might try that.  You could also  
do some reverse-engineering on the Alinco switcher that started the  
trend toward having that type of control back about 10 years ago:

http://www.eham.net/reviews/detail/765

It still gets good reviews, and I know a number of hams using them.

> I'm sure that it is possible to use switchers in receivers but I think
> that lots of effort would be required. I am not surprised if switchers
> are rare in receivers.

Depends on how wide the receiver front-end is, and what you're trying  
to hear.  :-)  I've seen lots of switchers that had fixed frequency  
noise outside of the bands desired for reception.

--
Nate Duehr
RemoveMEnateTakeThisOuTspamspamnatetech.com



2008\11\03@075244 by olin piclist

face picon face
Sean Breheny wrote:
> As a hobby project I have slowly been building a high-performance HF
> receiver over the last few years. I originally used a switching power
> supply in it. Granted, I'm only slightly beyond newbie when it comes
> to switching power supplies, but I have to say that I found it
> impossible to keep the harmonics from the switcher from making it into
> the receiver. I tried shielding and massive filtering on the input and
> output leads to no real avail. I did not try magnetic shielding,
> however the physical separation between the switcher and the rest of
> the receiver was such that I would find it hard to believe that there
> could be direct magnetic coupling.

It sounds like you tried everything except the one thing that should be at
the top of the list, which is proper grounding and attention to where the
high frequency loop currents go.  This is the most important single thing
for keeping any sort of switching noise from going elsewhere.

A few years ago I redesigned a receiver that had to decode the information
from two 434MHz receiver and pass the resulting data along over ethernet.
The original design used a 6 layer board with the digital section in a can.
The bottom layer formed one face of the can, and a separate piece of custom
fabricated metal was soldered over the digital and switching power supply
section.  Needless to say, this was a expensive solution.

My redesigned version replaced the analog data slicers with a dsPIC, used
two switching power supplies instead of one, and only a 4 layer open board
with no sheild.  However, I paid careful attention to where all the high
frequency loop currents were from the digital parts and the switching power
supplies, used one layer for a pervasive ground plane, and used sub ground
planes for noisy sub-sections.  In the end we beat the FCC emissions limit
by almost 15dB, and got a much lower noise floor from the two RF receivers.
The net result was that it could pick up transmissions from over twice as
far and cost 30% less to produce.


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

2008\11\03@085551 by Sean Breheny

face picon face
Hi Olin,

Well, the first thing I did was to design the switcher layout to try
to minimize radiated emissions. I also had a copper shield can over
the switcher components, which was connected to ground. However, I am
still learning when it comes to good board layout for switchers so I
suspect that I could have done a better job. I agree with you, though,
that shielding is a secondary measure - one should always start by
minimizing the radiation to begin with.

My receiver is a general coverage shortwave type covering 0.1 to
32MHz. The switcher was a National "simple switcher" series, I don't
remember the exact part number. I think it ran at 80kHz if I remember
correctly. Basically I could hear a small band of noise every 80kHz as
I tuned, well up into the HF spectrum. I think that the National part
probably placed such a high emphasis on efficiency that it turned on
its output stage very hard and fast, given that it produced audible
harmonics well above 10MHz.

The effect on the receiver was not overwhelming but definitely annoying.

Sean


On Mon, Nov 3, 2008 at 7:52 AM, Olin Lathrop <EraseMEolin_piclistspamspamspamBeGoneembedinc.com> wrote:
{Quote hidden}

> -

2008\11\03@085736 by Sean Breheny

face picon face
I should add that I have since changed over to a linear and it is
working much better. The project has dragged on for 3 years now and I
want to get it done so I am not going to go back and redesign the
switcher again. Next time I have to design one I will bear all this in
mind.

Sean


On Mon, Nov 3, 2008 at 8:55 AM, Sean Breheny <RemoveMEshb7KILLspamspamcornell.edu> wrote:
{Quote hidden}

>> --

2008\11\03@093404 by Martin

face
flavicon
face
Sean Breheny wrote:
> I should add that I have since changed over to a linear and it is
> working much better. The project has dragged on for 3 years now and I
> want to get it done so I am not going to go back and redesign the
> switcher again. Next time I have to design one I will bear all this in
> mind.
>
> Sean
>

In the future you may want to look into spread-spectrum switchers.
-
Martin

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