Lpc2000

Hi! I am in trouble trying to find a voltage regulator suitable for my 
project; my project features an LPC2138, a GPS and a radiomodem. When 
idle, it draws around 20-25 mA from the 3.3V source, 500 mA when 
working hard and with short (50 mS) peaks of up to 1.8A. The supply is 
a lead-acid 12V battery (can't change that), and occasionally, when the 
battery is charging, the input voltage will rise up to ~20V. The 
problem is the regulator efficiency. We were going for the LM2676-3.3V 
switching regulator, because it seemed simple and in range, but two 
things made it a poor choice: it draws about 4.3 mA from the battery 
just for its own supply, and its efficiency when the load is in the 20-
25 mA range is awful (less than 50%, not counting Iquiescent). I looked 
everywhere but I couldn't find any other switcher with better 
performance in these conditions (12V in, 3.3V out, 20-25 mA average 
load, but >1.5A capability). And there's a catch! The radiomodem is 
extremely sensitive to VCC getting lower than 3.3V especially in the 
current peaks! Also, it should be relatively easy to find in ~400 
quantities (i.e., Digikey, Mouser or your suggestion).

Any ideas?

Guille

Is this for use in an automotive environment?

Is 4.3mA or 50% efficiency when at low currents that big a deal?  What's 
the amp-hour rating of the battery, and how many other devices are using 
it?  How often does it get recharged?

What's your target price range for this setup?

-- Sean

At 07:49 PM 12/1/2005, Guillermo Prandi wrote:

>Hi! I am in trouble trying to find a voltage regulator suitable for my
>project; my project features an LPC2138, a GPS and a radiomodem. When
>idle, it draws around 20-25 mA from the 3.3V source, 500 mA when
>working hard and with short (50 mS) peaks of up to 1.8A. The supply is
>a lead-acid 12V battery (can't change that), and occasionally, when the
>battery is charging, the input voltage will rise up to ~20V. The
>problem is the regulator efficiency. We were going for the LM2676-3.3V
>switching regulator, because it seemed simple and in range, but two
>things made it a poor choice: it draws about 4.3 mA from the battery
>just for its own supply, and its efficiency when the load is in the 20-
>25 mA range is awful (less than 50%, not counting Iquiescent). I looked
>everywhere but I couldn't find any other switcher with better
>performance in these conditions (12V in, 3.3V out, 20-25 mA average
>load, but >1.5A capability). And there's a catch! The radiomodem is
>extremely sensitive to VCC getting lower than 3.3V especially in the
>current peaks! Also, it should be relatively easy to find in ~400
>quantities (i.e., Digikey, Mouser or your suggestion).
>
>Any ideas?
>
>Guille

Guillermo Prandi wrote:

>Hi! I am in trouble trying to find a voltage regulator suitable for my 
>project; my project features an LPC2138, a GPS and a radiomodem. When 
>idle, it draws around 20-25 mA from the 3.3V source, 500 mA when 
>working hard and with short (50 mS) peaks of up to 1.8A. The supply is 
>a lead-acid 12V battery (can't change that), and occasionally, when the 
>battery is charging, the input voltage will rise up to ~20V. The 
>problem is the regulator efficiency. We were going for the LM2676-3.3V 
>switching regulator, because it seemed simple and in range, but two 
>things made it a poor choice: it draws about 4.3 mA from the battery 
>just for its own supply, and its efficiency when the load is in the 20-
>25 mA range is awful (less than 50%, not counting Iquiescent). I looked 
>everywhere but I couldn't find any other switcher with better 
>performance in these conditions (12V in, 3.3V out, 20-25 mA average 
>load, but >1.5A capability). And there's a catch! The radiomodem is 
>extremely sensitive to VCC getting lower than 3.3V especially in the 
>current peaks! Also, it should be relatively easy to find in ~400 
>quantities (i.e., Digikey, Mouser or your suggestion).
>
>  
>
Keep in mind that most off-the-shelf supplies are intended for general 
purpose use / short run / prototypes.  Anyone doing significant 
production quantities is not willing to accept the built-in premium cost 
for the convenience of not designing your own.  I stopped looking at 
off-the-shelf supplies for my boards / systems a long time ago.

My reaction from what you were saying was that you need multiple 
supplies rather than a single supply.  Different regulator types for 
each current load profile.  Most switching supplies require a minimum 
load on them otherwise they can go into conduction (switching gate left 
on), you hear a term called "discontinuous mode", that helps prevent 
stalling.

What it sound like to me is that you need a modest supply to run the 
processors circuitry, then a larger supply to drive the heavier loads.  
The larger supply could be one that can be shutdown, thereby reducing 
standby current (minimum load to avoid stalling).

FWIW, 400 units, and assuming a $10 premium (wholesaler profit), that 
comes out to $4000.  I think that if you approach a good power suppy 
consultant, he would be more than happy to take $4000 to design you a 
supply which could only cost you one half of what an off-the-shelf model 
would be.

I know of one in my area (Pennsylvania) and deal with him from time-time...

Regards,

TomW

-- 
Tom Walsh - WN3L - Embedded Systems Consultant
http://openhardware.net, http://cyberiansoftware.com
"Windows? No thanks, I have work to do..."
----------------------------------------------------

On Fri, Dec 02, 2005 at 12:49:42AM -0000, Guillermo Prandi wrote:
> Hi! I am in trouble trying to find a voltage regulator suitable for my 
> project; my project features an LPC2138, a GPS and a radiomodem. When 

How about this one?

http://focus.ti.com/docs/prod/folders/print/tps62111.html

-- 
Clyde Stubbs                     |            HI-TECH Software
Email: clyde@...          |          Phone            Fax
WWW:   http://www.htsoft.com/    | USA: (408) 490 2885  (408) 490 2885
PGP:   finger clyde@...   | AUS: +61 7 3722 7777 +61 7 3722 7778
---------------------------------------------------------------------------
HI-TECH C: compiling the real world.

The battery will be recharged after... 21 days of continuous 
operation!!!! You can imagine how big a deal is a couple of mAmps in 
such a long time... The battery must not get below 10.5V or else it 
would become unusable. Even worse, acid-lead batteries, though less 
than other kinds of rechargeable batteries, do self-discharge 
considerably in such 'long' periods. I also have a limit on how big 
the battery can be (we're targetting a 12V 12A/H battery as the 
heavier one we can carry).

The devices are pretty much what I listed below, LPC + GPS + RM, plus 
obvious control circuitery, serial ports, an occasional led flash, 
etc. (no display, no keyboard). The worst part comes from the 
radiomodem, which draws from <5 mA when standby to 200-300 mA 
operating (sending/receiving) and with 1.6A peaks.

Maximum acceptable price for the power supply part of the circuit 
(including inductors, etc.) would be around $15.

Guille

--- In lpc2000@yahoogroups.com, Sean <embeddedrelated@w...> wrote:
>
> 
> Is this for use in an automotive environment?
> 
> Is 4.3mA or 50% efficiency when at low currents that big a deal?  
What's 
> the amp-hour rating of the battery, and how many other devices are 
using 
> it?  How often does it get recharged?
> 
> What's your target price range for this setup?
> 
> -- Sean
> 
> At 07:49 PM 12/1/2005, Guillermo Prandi wrote:
> >Hi! I am in trouble trying to find a voltage regulator suitable 
for my
> >project; my project features an LPC2138, a GPS and a radiomodem. 
When
> >idle, it draws around 20-25 mA from the 3.3V source, 500 mA when
> >working hard and with short (50 mS) peaks of up to 1.8A. The 
supply is
> >a lead-acid 12V battery (can't change that), and occasionally, 
when the
> >battery is charging, the input voltage will rise up to ~20V. The
> >problem is the regulator efficiency. We were going for the LM2676-
3.3V
> >switching regulator, because it seemed simple and in range, but two
> >things made it a poor choice: it draws about 4.3 mA from the 
battery
> >just for its own supply, and its efficiency when the load is in 
the 20-
> >25 mA range is awful (less than 50%, not counting Iquiescent). I 
looked
> >everywhere but I couldn't find any other switcher with better
> >performance in these conditions (12V in, 3.3V out, 20-25 mA average
> >load, but >1.5A capability). And there's a catch! The radiomodem is
> >extremely sensitive to VCC getting lower than 3.3V especially in 
the

> >current peaks! Also, it should be relatively easy to find in ~400
> >quantities (i.e., Digikey, Mouser or your suggestion).
> >
> >Any ideas?
> >
> >Guille
>

I thought of that, Tom (separate supplies), but I realized that I 
wouldn't get anything from it, because there is this single device 
that goes from <5 mA to 1.6A, and that is the radiomodem. I can't say 
when the RM will draw <5 mA and when will it draw 1.6A. This is for 
the GSM protocol to decide. Therefore, whichever power supply I'd set 
up for the radiomodem must be efficient for pretty much the same 
range as one supply that would feed the rest of the circuit as well 
(which by the way won't take more than 80-90 mA ever).

It is tempting to have a power supply specially tailored for our 
needs. However my schedule has become incredibly short, with the 
additional difficulty that we are based in Argentina, so it is hard 
to arrange such things. However, feel free to lend me your 
acquaintance's e-mail address through a private message.

Guille

--- In lpc2000@yahoogroups.com, Tom Walsh <tom@o...> wrote:
>
> Guillermo Prandi wrote:
> 
> >Hi! I am in trouble trying to find a voltage regulator suitable 
for my 
> >project; my project features an LPC2138, a GPS and a radiomodem. 
When 
> >idle, it draws around 20-25 mA from the 3.3V source, 500 mA when 
> >working hard and with short (50 mS) peaks of up to 1.8A. The 
supply is 
> >a lead-acid 12V battery (can't change that), and occasionally, 
when the 
> >battery is charging, the input voltage will rise up to ~20V. The 
> >problem is the regulator efficiency. We were going for the LM2676-
3.3V 
> >switching regulator, because it seemed simple and in range, but 
two 
> >things made it a poor choice: it draws about 4.3 mA from the 
battery 
> >just for its own supply, and its efficiency when the load is in 
the 20-
> >25 mA range is awful (less than 50%, not counting Iquiescent). I 
looked 
> >everywhere but I couldn't find any other switcher with better 
> >performance in these conditions (12V in, 3.3V out, 20-25 mA 
average 
> >load, but >1.5A capability). And there's a catch! The radiomodem 
is 
> >extremely sensitive to VCC getting lower than 3.3V especially in 
the 
> >current peaks! Also, it should be relatively easy to find in ~400 
> >quantities (i.e., Digikey, Mouser or your suggestion).
> >
> >  
> >
> Keep in mind that most off-the-shelf supplies are intended for 
general 
> purpose use / short run / prototypes.  Anyone doing significant 
> production quantities is not willing to accept the built-in premium 
cost 
> for the convenience of not designing your own.  I stopped looking 
at 
> off-the-shelf supplies for my boards / systems a long time ago.
> 
> My reaction from what you were saying was that you need multiple 
> supplies rather than a single supply.  Different regulator types 
for 
> each current load profile.  Most switching supplies require a 
minimum 
> load on them otherwise they can go into conduction (switching gate 
left 
> on), you hear a term called "discontinuous mode", that helps 
prevent 
> stalling.
> 
> What it sound like to me is that you need a modest supply to run 
the 
> processors circuitry, then a larger supply to drive the heavier 
loads.  
> The larger supply could be one that can be shutdown, thereby 
reducing 
> standby current (minimum load to avoid stalling).
> 
> FWIW, 400 units, and assuming a $10 premium (wholesaler profit), 
that 
> comes out to $4000.  I think that if you approach a good power 
suppy 
> consultant, he would be more than happy to take $4000 to design you 
a 
> supply which could only cost you one half of what an off-the-shelf 
model 
> would be.
> 
> I know of one in my area (Pennsylvania) and deal with him from time-
time...

> 
> Regards,
> 
> TomW
> 
> -- 
> Tom Walsh - WN3L - Embedded Systems Consultant
> http://openhardware.net, http://cyberiansoftware.com
> "Windows? No thanks, I have work to do..."
> ----------------------------------------------------
>

Thanks, Clyde. Yes, this is more like it. However it seems a little 
hard to get. None of the TI distributors seem to have it in stock, 
though it seems that it can be bought directly from TI (with a 6 
weeks lead time). I'll look into it tomorrow.

Guille

--- In lpc2000@yahoogroups.com, Clyde Stubbs <clyde@h...> wrote:
>
> On Fri, Dec 02, 2005 at 12:49:42AM -0000, Guillermo Prandi wrote:
> > Hi! I am in trouble trying to find a voltage regulator suitable 
for my 
> > project; my project features an LPC2138, a GPS and a radiomodem. 
When 
> 
> How about this one?
> 
> http://focus.ti.com/docs/prod/folders/print/tps62111.html
> 
> -- 
> Clyde Stubbs                     |            HI-TECH Software
> Email: clyde@h...          |          Phone            Fax
> WWW:   http://www.htsoft.com/    | USA: (408) 490 2885  (408) 490 
2885
> PGP:   finger clyde@h...   | AUS: +61 7 3722 7777 +61 7 3722 7778
> --------------------------------------------------------------------
-------
> HI-TECH C: compiling the real world.
>

Guille wrote,

> Hi! I am in trouble trying to find a voltage regulator suitable for my
> project; my project features an LPC2138, a GPS and a radiomodem. When
> idle, it draws around 20-25 mA from the 3.3V source, 500 mA when
> working hard and with short (50 mS) peaks of up to 1.8A. The supply is
> a lead-acid 12V battery (can't change that), and occasionally, when the
> battery is charging, the input voltage will rise up to ~20V. The
> problem is the regulator efficiency. We were going for the LM2676-3.3V
> switching regulator, because it seemed simple and in range, but two
> things made it a poor choice: it draws about 4.3 mA from the battery
> just for its own supply, and its efficiency when the load is in the 20-
> 25 mA range is awful (less than 50%, not counting Iquiescent). I looked
> everywhere but I couldn't find any other switcher with better
> performance in these conditions (12V in, 3.3V out, 20-25 mA average
> load, but >1.5A capability). And there's a catch! The radiomodem is
> extremely sensitive to VCC getting lower than 3.3V especially in the
> current peaks! Also, it should be relatively easy to find in ~400
> quantities (i.e., Digikey, Mouser or your suggestion).

I've used the MAX5035 for automotive apps.  Nice part.
http://www.maxim-ic.com/solutions/automotive/parts.mvp/scpk/1458/pl_pk/0

You might consider the MAX5090, it goes up to 2A.  The input voltage range
is 6.5V to 72V.

Joel

Thanks, Joel. Efficiency on those chips seems still very low (around 
50% for my circuit's average load, 15 mA), though the low quiescent 
current seems tempting.

Guille

--- In lpc2000@yahoogroups.com, "Joel Winarske" <joelw@i...> wrote:
>
> Guille wrote,
> 
> > Hi! I am in trouble trying to find a voltage regulator suitable 
for my
> > project; my project features an LPC2138, a GPS and a radiomodem. 
When
> > idle, it draws around 20-25 mA from the 3.3V source, 500 mA when
> > working hard and with short (50 mS) peaks of up to 1.8A. The 
supply is
> > a lead-acid 12V battery (can't change that), and occasionally, 
when the
> > battery is charging, the input voltage will rise up to ~20V. The
> > problem is the regulator efficiency. We were going for the LM2676-
3.3V
> > switching regulator, because it seemed simple and in range, but 
two
> > things made it a poor choice: it draws about 4.3 mA from the 
battery
> > just for its own supply, and its efficiency when the load is in 
the 20-
> > 25 mA range is awful (less than 50%, not counting Iquiescent). I 
looked
> > everywhere but I couldn't find any other switcher with better
> > performance in these conditions (12V in, 3.3V out, 20-25 mA 
average
> > load, but >1.5A capability). And there's a catch! The radiomodem 
is
> > extremely sensitive to VCC getting lower than 3.3V especially in 
the
> > current peaks! Also, it should be relatively easy to find in ~400
> > quantities (i.e., Digikey, Mouser or your suggestion).
> 
> I've used the MAX5035 for automotive apps.  Nice part.
> http://www.maxim-
ic.com/solutions/automotive/parts.mvp/scpk/1458/pl_pk/0
> 
> You might consider the MAX5090, it goes up to 2A.  The input 
voltage range

> is 6.5V to 72V.
> 
> Joel
>

What type of efficiency does a linear regulator give you when setup in a 
switching-style topology for low currents?

Check out L7805C datasheet figure 27 in case you don't know what I'm 
talking about.

While we're on offtopic, what diodes do you guys recommend using, 
especially for lithium backup purposes?  Most diodes that I see that are 
frequently used have large forward voltage drops for any non-trivial 
current draw.

-- Sean

At 12:50 PM 12/2/2005, Guillermo Prandi wrote:

>Thanks, Joel. Efficiency on those chips seems still very low (around
>50% for my circuit's average load, 15 mA), though the low quiescent
>current seems tempting.
>
>Guille
>
>--- In lpc2000@yahoogroups.com, "Joel Winarske" <joelw@i...> wrote:
> >
> > Guille wrote,
> >
> > > Hi! I am in trouble trying to find a voltage regulator suitable
>for my
> > > project; my project features an LPC2138, a GPS and a radiomodem.
>When
> > > idle, it draws around 20-25 mA from the 3.3V source, 500 mA when
> > > working hard and with short (50 mS) peaks of up to 1.8A. The
>supply is
> > > a lead-acid 12V battery (can't change that), and occasionally,
>when the
> > > battery is charging, the input voltage will rise up to ~20V. The
> > > problem is the regulator efficiency. We were going for the LM2676-
>3.3V
> > > switching regulator, because it seemed simple and in range, but
>two
> > > things made it a poor choice: it draws about 4.3 mA from the
>battery
> > > just for its own supply, and its efficiency when the load is in
>the 20-
> > > 25 mA range is awful (less than 50%, not counting Iquiescent). I
>looked
> > > everywhere but I couldn't find any other switcher with better
> > > performance in these conditions (12V in, 3.3V out, 20-25 mA
>average
> > > load, but >1.5A capability). And there's a catch! The radiomodem
>is
> > > extremely sensitive to VCC getting lower than 3.3V especially in
>the
> > > current peaks! Also, it should be relatively easy to find in ~400
> > > quantities (i.e., Digikey, Mouser or your suggestion).
> >
> > I've used the MAX5035 for automotive apps.  Nice part.
> > <http://www.maxim->http://www.maxim-
>ic.com/solutions/automotive/parts.mvp/scpk/1458/pl_pk/0
> >
> > You might consider the MAX5090, it goes up to 2A.  The input
>voltage range
> > is 6.5V to 72V.
> >
> > Joel
> >
>
>
>
>
>
>
>
>SPONSORED LINKS
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><http://groups.yahoo.com/gads?t=ms&k=Microcontrollers&w1=Microprocessor&w2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=DvJVNqC_pqRTm8Xq01nxwg>Microcontrollers 
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Mmm.... I'd have to check it out. I'll probably try it this Monday. 
It looks nice because it uses very common components.

Guille

--- In lpc2000@yahoogroups.com, Sean <embeddedrelated@w...> wrote:
>
> 
> What type of efficiency does a linear regulator give you when setup 
in a 
> switching-style topology for low currents?
> 
> Check out L7805C datasheet figure 27 in case you don't know what 
I'm 
> talking about.
> 
> While we're on offtopic, what diodes do you guys recommend using, 
> especially for lithium backup purposes?  Most diodes that I see 
that are 
> frequently used have large forward voltage drops for any non-
trivial 
> current draw.
> 
> -- Sean
> 
> At 12:50 PM 12/2/2005, Guillermo Prandi wrote:
> >Thanks, Joel. Efficiency on those chips seems still very low 
(around
> >50% for my circuit's average load, 15 mA), though the low quiescent
> >current seems tempting.
> >
> >Guille
> >
> >--- In lpc2000@yahoogroups.com, "Joel Winarske" <joelw@i...> wrote:
> > >
> > > Guille wrote,
> > >
> > > > Hi! I am in trouble trying to find a voltage regulator 
suitable
> >for my
> > > > project; my project features an LPC2138, a GPS and a 
radiomodem.
> >When
> > > > idle, it draws around 20-25 mA from the 3.3V source, 500 mA 
when
> > > > working hard and with short (50 mS) peaks of up to 1.8A. The
> >supply is
> > > > a lead-acid 12V battery (can't change that), and occasionally,
> >when the
> > > > battery is charging, the input voltage will rise up to ~20V. 
The
> > > > problem is the regulator efficiency. We were going for the 
LM2676-
> >3.3V
> > > > switching regulator, because it seemed simple and in range, 
but
> >two
> > > > things made it a poor choice: it draws about 4.3 mA from the
> >battery
> > > > just for its own supply, and its efficiency when the load is 
in
> >the 20-
> > > > 25 mA range is awful (less than 50%, not counting 
Iquiescent). I
> >looked
> > > > everywhere but I couldn't find any other switcher with better
> > > > performance in these conditions (12V in, 3.3V out, 20-25 mA
> >average
> > > > load, but >1.5A capability). And there's a catch! The 
radiomodem
> >is
> > > > extremely sensitive to VCC getting lower than 3.3V especially 
in
> >the
> > > > current peaks! Also, it should be relatively easy to find in 
~400
> > > > quantities (i.e., Digikey, Mouser or your suggestion).
> > >
> > > I've used the MAX5035 for automotive apps.  Nice part.
> > > <http://www.maxim->http://www.maxim-
> >ic.com/solutions/automotive/parts.mvp/scpk/1458/pl_pk/0
> > >
> > > You might consider the MAX5090, it goes up to 2A.  The input
> >voltage range
> > > is 6.5V to 72V.
> > >
> > > Joel
> > >
> >
> >
> >
> >
> >
> >
> >
> >SPONSORED LINKS
> ><http://groups.yahoo.com/gads?
t=ms&k=Microprocessor&w1=Microprocessor&w2=Microcontrollers&w3=Pic+mic
rocontrollers&w4=8051+microprocessor&c=4&s=93&.sig=tsVC-
J9hJ5qyXg0WPR0l6g>Microprocessor 
> ><http://groups.yahoo.com/gads?
t=ms&k=Microcontrollers&w1=Microprocessor&w2=Microcontrollers&w3=Pic+m
icrocontrollers&w4=8051+microprocessor&c=4&s=93&.sig=DvJVNqC_pqRTm8Xq0
1nxwg>Microcontrollers 
> ><http://groups.yahoo.com/gads?
t=ms&k=Pic+microcontrollers&w1=Microprocessor&w2=Microcontrollers&w3=P
ic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=TpkoX4KofDJ7c
6LyBvUqVQ>Pic 
> >microcontrollers
> ><http://groups.yahoo.com/gads?
t=ms&k=8051+microprocessor&w1=Microprocessor&w2=Microcontrollers&w3=Pi
c+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=1Ipf1Fjfbd_HVI
lekkDP-A>8051 
> >microprocessor
> >
> >
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> > <http://docs.yahoo.com/info/terms/>Yahoo! Terms of Service.
> >
> >
> >----------
>

Sean wrote:

>What type of efficiency does a linear regulator give you when setup in a 
>switching-style topology for low currents?
>
>  
>
Figure about 30%, maybe %40, efficiency for a linear, three terminal 
regulator.  It is not possible to use a Linear Regulator as a switched 
element...


TomW



>Check out L7805C datasheet figure 27 in case you don't know what I'm 
>talking about.
>
>While we're on offtopic, what diodes do you guys recommend using, 
>especially for lithium backup purposes?  Most diodes that I see that are 
>frequently used have large forward voltage drops for any non-trivial 
>current draw.
>
>-- Sean
>
>At 12:50 PM 12/2/2005, Guillermo Prandi wrote:
>  
>
>>Thanks, Joel. Efficiency on those chips seems still very low (around
>>50% for my circuit's average load, 15 mA), though the low quiescent
>>current seems tempting.
>>
>>Guille
>>
>>--- In lpc2000@yahoogroups.com, "Joel Winarske" <joelw@i...> wrote:
>>    
>>
>>>Guille wrote,
>>>
>>>      
>>>
>>>>Hi! I am in trouble trying to find a voltage regulator suitable
>>>>        
>>>>
>>for my
>>    
>>
>>>>project; my project features an LPC2138, a GPS and a radiomodem.
>>>>        
>>>>
>>When
>>    
>>
>>>>idle, it draws around 20-25 mA from the 3.3V source, 500 mA when
>>>>working hard and with short (50 mS) peaks of up to 1.8A. The
>>>>        
>>>>
>>supply is
>>    
>>
>>>>a lead-acid 12V battery (can't change that), and occasionally,
>>>>        
>>>>
>>when the
>>    
>>
>>>>battery is charging, the input voltage will rise up to ~20V. The
>>>>problem is the regulator efficiency. We were going for the LM2676-
>>>>        
>>>>
>>3.3V
>>    
>>
>>>>switching regulator, because it seemed simple and in range, but
>>>>        
>>>>
>>two
>>    
>>
>>>>things made it a poor choice: it draws about 4.3 mA from the
>>>>        
>>>>
>>battery
>>    
>>
>>>>just for its own supply, and its efficiency when the load is in
>>>>        
>>>>
>>the 20-
>>    
>>
>>>>25 mA range is awful (less than 50%, not counting Iquiescent). I
>>>>        
>>>>
>>looked
>>    
>>
>>>>everywhere but I couldn't find any other switcher with better
>>>>performance in these conditions (12V in, 3.3V out, 20-25 mA
>>>>        
>>>>
>>average
>>    
>>
>>>>load, but >1.5A capability). And there's a catch! The radiomodem
>>>>        
>>>>
>>is
>>    
>>
>>>>extremely sensitive to VCC getting lower than 3.3V especially in
>>>>        
>>>>
>>the
>>    
>>
>>>>current peaks! Also, it should be relatively easy to find in ~400
>>>>quantities (i.e., Digikey, Mouser or your suggestion).
>>>>        
>>>>
>>>I've used the MAX5035 for automotive apps.  Nice part.
>>><http://www.maxim->http://www.maxim-
>>>      
>>>
>>ic.com/solutions/automotive/parts.mvp/scpk/1458/pl_pk/0
>>    
>>
>>>You might consider the MAX5090, it goes up to 2A.  The input
>>>      
>>>
>>voltage range
>>    
>>
>>>is 6.5V to 72V.
>>>
>>>Joel
>>>
>>>      
>>>
>>
>>
>>
>>
>>
>>SPONSORED LINKS
>><http://groups.yahoo.com/gads?t=ms&k=Microprocessor&w1=Microprocessor&w2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=tsVC-J9hJ5qyXg0WPR0l6g>Microprocessor 
>><http://groups.yahoo.com/gads?t=ms&k=Microcontrollers&w1=Microprocessor&w2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=DvJVNqC_pqRTm8Xq01nxwg>Microcontrollers 
>><http://groups.yahoo.com/gads?t=ms&k=Pic+microcontrollers&w1=Microprocessor&w2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=TpkoX4KofDJ7c6LyBvUqVQ>Pic 
>>microcontrollers
>><http://groups.yahoo.com/gads?t=ms&k=8051+microprocessor&w1=Microprocessor&w2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=1Ipf1Fjfbd_HVIlekkDP-A>8051 
>>microprocessor
>>
>>
>>----------
>>YAHOO! GROUPS LINKS
>>
>>   *  Visit your group "<http://groups.yahoo.com/group/lpc2000>lpc2000" 
>>on the web.
>>   *
>>   *  To unsubscribe from this group, send an email to:
>>   * 
>><mailto:lpc2000-unsubscribe@yahoogroups.com?subject=Unsubscribe>lpc2000-unsubscribe@yahoogroups.com 
>>
>>   *
>>   *  Your use of Yahoo! Groups is subject to the 
>><http://docs.yahoo.com/info/terms/>Yahoo! Terms of Service.
>>
>>
>>----------
>>    
>>
>
>
>
>
> 
>Yahoo! Groups Links
>
>
>
> 
>
>
>
>  
>


-- 
Tom Walsh - WN3L - Embedded Systems Consultant
http://openhardware.net, http://cyberiansoftware.com
"Windows? No thanks, I have work to do..."
----------------------------------------------------

Tom:

I'm confused by your response.

The datasheet clearly shows that it is possible, it even gives the the 
schematic to do it.  In effect you are building a switching regulator, the 
same way that a premade one works, except with a much lower switching 
frequency.

I'd imagine that for high loads the efficiency isn't as good as a real 
switching regulator (due to the lower switching frequency), but it is much 
better than linear.  I do not, however, know how well it performs with low 
currents.

Guillermo:

What is the duty cycle going to be on your device?  i.e. how much time will 
it spend in idle mode vs low power vs full power mode?  Perhaps asking the 
question a different way:  how much power (in watt-hours say) do you expect 
to use between recharges?

-- Sean

At 01:16 AM 12/3/2005, Tom Walsh wrote:

>Sean wrote:
>
> >What type of efficiency does a linear regulator give you when setup in a
> >switching-style topology for low currents?
> >
> >
> >
>Figure about 30%, maybe %40, efficiency for a linear, three terminal
>regulator.  It is not possible to use a Linear Regulator as a switched
>element...
>
>
>TomW
>
>
>
> >Check out L7805C datasheet figure 27 in case you don't know what I'm
> >talking about.
> >
> >While we're on offtopic, what diodes do you guys recommend using,
> >especially for lithium backup purposes?  Most diodes that I see that are
> >frequently used have large forward voltage drops for any non-trivial
> >current draw.
> >
> >-- Sean
> >
> >At 12:50 PM 12/2/2005, Guillermo Prandi wrote:
> >
> >
> >>Thanks, Joel. Efficiency on those chips seems still very low (around
> >>50% for my circuit's average load, 15 mA), though the low quiescent
> >>current seems tempting.
> >>
> >>Guille
> >>
> >>--- In lpc2000@yahoogroups.com, "Joel Winarske" <joelw@i...> wrote:
> >>
> >>
> >>>Guille wrote,
> >>>
> >>>
> >>>
> >>>>Hi! I am in trouble trying to find a voltage regulator suitable
> >>>>
> >>>>
> >>for my
> >>
> >>
> >>>>project; my project features an LPC2138, a GPS and a radiomodem.
> >>>>
> >>>>
> >>When
> >>
> >>
> >>>>idle, it draws around 20-25 mA from the 3.3V source, 500 mA when
> >>>>working hard and with short (50 mS) peaks of up to 1.8A. The
> >>>>
> >>>>
> >>supply is
> >>
> >>
> >>>>a lead-acid 12V battery (can't change that), and occasionally,
> >>>>
> >>>>
> >>when the
> >>
> >>
> >>>>battery is charging, the input voltage will rise up to ~20V. The
> >>>>problem is the regulator efficiency. We were going for the LM2676-
> >>>>
> >>>>
> >>3.3V
> >>
> >>
> >>>>switching regulator, because it seemed simple and in range, but
> >>>>
> >>>>
> >>two
> >>
> >>
> >>>>things made it a poor choice: it draws about 4.3 mA from the
> >>>>
> >>>>
> >>battery
> >>
> >>
> >>>>just for its own supply, and its efficiency when the load is in
> >>>>
> >>>>
> >>the 20-
> >>
> >>
> >>>>25 mA range is awful (less than 50%, not counting Iquiescent). I
> >>>>
> >>>>
> >>looked
> >>
> >>
> >>>>everywhere but I couldn't find any other switcher with better
> >>>>performance in these conditions (12V in, 3.3V out, 20-25 mA
> >>>>
> >>>>
> >>average
> >>
> >>
> >>>>load, but >1.5A capability). And there's a catch! The radiomodem
> >>>>
> >>>>
> >>is
> >>
> >>
> >>>>extremely sensitive to VCC getting lower than 3.3V especially in
> >>>>
> >>>>
> >>the
> >>
> >>
> >>>>current peaks! Also, it should be relatively easy to find in ~400
> >>>>quantities (i.e., Digikey, Mouser or your suggestion).
> >>>>
> >>>>
> >>>I've used the MAX5035 for automotive apps.  Nice part.
> >>><<http://www.maxim->http://www.maxim->http://www.maxim-
> >>>
> >>>
> >>ic.com/solutions/automotive/parts.mvp/scpk/1458/pl_pk/0
> >>
> >>
> >>>You might consider the MAX5090, it goes up to 2A.  The input
> >>>
> >>>
> >>voltage range
> >>
> >>
> >>>is 6.5V to 72V.
> >>>
> >>>Joel
> >>>
> >>>
> >>>
> >>
> >>
> >>
> >>
> >>
> >>SPONSORED LINKS
> >><<http://groups.yahoo.com/gads?t=ms&k=Microprocessor&w1=Microprocessor&w 
> 2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=tsVC-J9hJ5qyXg0WPR0l6g>http://groups.yahoo.com/gads?t=ms&k=Microprocessor&w1=Microprocessor&w2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=tsVC-J9hJ5qyXg0WPR0l6g>Microprocessor 
>
> >><<http://groups.yahoo.com/gads?t=ms&k=Microcontrollers&w1=Microprocessor 
> &w2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=DvJVNqC_pqRTm8Xq01nxwg>http://groups.yahoo.com/gads?t=ms&k=Microcontrollers&w1=Microprocessor&w2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=DvJVNqC_pqRTm8Xq01nxwg>Microcontrollers 
>
> >><<http://groups.yahoo.com/gads?t=ms&k=Pic+microcontrollers&w1=Microproce 
> ssor&w2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=TpkoX4KofDJ7c6LyBvUqVQ>http://groups.yahoo.com/gads?t=ms&k=Pic+microcontrollers&w1=Microprocessor&w2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=TpkoX4KofDJ7c6LyBvUqVQ>Pic 
>
> >>microcontrollers
> >><<http://groups.yahoo.com/gads?t=ms&k=8051+microprocessor&w1=Microproces 
> sor&w2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=1Ipf1Fjfbd_HVIlekkDP-A>http://groups.yahoo.com/gads?t=ms&k=8051+microprocessor&w1=Microprocessor&w2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=1Ipf1Fjfbd_HVIlekkDP-A>8051 
>
> >>microprocessor
> >>
> >>
> >>----------
> >>YAHOO! GROUPS LINKS
> >>
> >>   *  Visit your group 
> "<<http://groups.yahoo.com/group/lpc2000>http://groups.yahoo.com/group/lpc2000>lpc2000" 
>
> >>on the web.
> >>   *
> >>   *  To unsubscribe from this group, send an email to:
> >>   *
> >><mailto:lpc2000-unsubscribe@yahoogroups.com?subject=Unsubscribe>lpc2000- 
> unsubscribe@yahoogroups.com
> >>
> >>   *
> >>   *  Your use of Yahoo! Groups is subject to the
> >><<http://docs.yahoo.com/info/terms/>http://docs.yahoo.com/info/terms/>Ya 
> hoo! Terms of Service.
> >>
> >>
> >>----------
> >>
> >>
> >
> >
> >
> >
> >
> >Yahoo! Groups Links
> >
> >
> >
> >
> >
> >
> >
> >
> >
>
>
>--
>Tom Walsh - WN3L - Embedded Systems Consultant
><http://openhardware.net,>http://openhardware.net, http://cyberiansoftware.com
>"Windows? No thanks, I have work to do..."
>----------------------------------------------------
>
>
>
>
>SPONSORED LINKS
><http://groups.yahoo.com/gads?t=ms&k=Microprocessor&w1=Microprocessor&w2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=tsVC-J9hJ5qyXg0WPR0l6g>Microprocessor 
><http://groups.yahoo.com/gads?t=ms&k=Microcontrollers&w1=Microprocessor&w2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=DvJVNqC_pqRTm8Xq01nxwg>Microcontrollers 
><http://groups.yahoo.com/gads?t=ms&k=Pic+microcontrollers&w1=Microprocessor&w2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=TpkoX4KofDJ7c6LyBvUqVQ>Pic 
>microcontrollers
><http://groups.yahoo.com/gads?t=ms&k=8051+microprocessor&w1=Microprocessor&w2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=1Ipf1Fjfbd_HVIlekkDP-A>8051 
>microprocessor
>
>
>----------
>YAHOO! GROUPS LINKS
>
>    *  Visit your group "<http://groups.yahoo.com/group/lpc2000>lpc2000" 
> on the web.
>    *
>    *  To unsubscribe from this group, send an email to:
>    * 
> <mailto:lpc2000-unsubscribe@yahoogroups.com?subject=Unsubscribe>lpc2000-unsubscribe@yahoogroups.com 
>
>    *
>    *  Your use of Yahoo! Groups is subject to the 
> <http://docs.yahoo.com/info/terms/>Yahoo! Terms of Service.
>
>
>----------

Sean wrote:

>Tom:
>
>I'm confused by your response.
>
>The datasheet clearly shows that it is possible, it even gives the the 
>schematic to do it.  In effect you are building a switching regulator, the 
>same way that a premade one works, except with a much lower switching 
>frequency.
>
>  
>
Read the schematic, it is a "trick".

They are using the L78xx as a control element to govern the pulse width 
of the 2N3789 pass transistor.  The PNP transistor is being used as the 
switch element.  When the voltage across the 2000ufd cap drops below the 
L78xx output voltage, the L78xx begins to draw current at its' input, 
thus causing the 2N3789 to go into saturation, which in turn dumps 
current into the inductor.

No, the app sheet just shows you a goofy switching regulator.  It _is 
not_ an L78xx switching regulator.  I would not expect efficiencies 
above the 70% range with a bipolar switch element (Vce drop causes heat 
loss).


TomW




>I'd imagine that for high loads the efficiency isn't as good as a real 
>switching regulator (due to the lower switching frequency), but it is much 
>better than linear.  I do not, however, know how well it performs with low 
>currents.
>
>Guillermo:
>
>What is the duty cycle going to be on your device?  i.e. how much time will 
>it spend in idle mode vs low power vs full power mode?  Perhaps asking the 
>question a different way:  how much power (in watt-hours say) do you expect 
>to use between recharges?
>
>-- Sean
>
>At 01:16 AM 12/3/2005, Tom Walsh wrote:
>  
>
>>Sean wrote:
>>
>>    
>>
>>>What type of efficiency does a linear regulator give you when setup in a
>>>switching-style topology for low currents?
>>>
>>>
>>>
>>>      
>>>
>>Figure about 30%, maybe %40, efficiency for a linear, three terminal
>>regulator.  It is not possible to use a Linear Regulator as a switched
>>element...
>>
>>
>>TomW
>>
>>
>>
>>    
>>
>>>Check out L7805C datasheet figure 27 in case you don't know what I'm
>>>talking about.
>>>
>>>While we're on offtopic, what diodes do you guys recommend using,
>>>especially for lithium backup purposes?  Most diodes that I see that are
>>>frequently used have large forward voltage drops for any non-trivial
>>>current draw.
>>>
>>>-- Sean
>>>
>>>At 12:50 PM 12/2/2005, Guillermo Prandi wrote:
>>>
>>>
>>>      
>>>
>>>>Thanks, Joel. Efficiency on those chips seems still very low (around
>>>>50% for my circuit's average load, 15 mA), though the low quiescent
>>>>current seems tempting.
>>>>
>>>>Guille
>>>>
>>>>--- In lpc2000@yahoogroups.com, "Joel Winarske" <joelw@i...> wrote:
>>>>
>>>>
>>>>        
>>>>
>>>>>Guille wrote,
>>>>>
>>>>>
>>>>>
>>>>>          
>>>>>
>>>>>>Hi! I am in trouble trying to find a voltage regulator suitable
>>>>>>
>>>>>>
>>>>>>            
>>>>>>
>>>>for my
>>>>
>>>>
>>>>        
>>>>
>>>>>>project; my project features an LPC2138, a GPS and a radiomodem.
>>>>>>
>>>>>>
>>>>>>            
>>>>>>
>>>>When
>>>>
>>>>
>>>>        
>>>>
>>>>>>idle, it draws around 20-25 mA from the 3.3V source, 500 mA when
>>>>>>working hard and with short (50 mS) peaks of up to 1.8A. The
>>>>>>
>>>>>>
>>>>>>            
>>>>>>
>>>>supply is
>>>>
>>>>
>>>>        
>>>>
>>>>>>a lead-acid 12V battery (can't change that), and occasionally,
>>>>>>
>>>>>>
>>>>>>            
>>>>>>
>>>>when the
>>>>
>>>>
>>>>        
>>>>
>>>>>>battery is charging, the input voltage will rise up to ~20V. The
>>>>>>problem is the regulator efficiency. We were going for the LM2676-
>>>>>>
>>>>>>
>>>>>>            
>>>>>>
>>>>3.3V
>>>>
>>>>
>>>>        
>>>>
>>>>>>switching regulator, because it seemed simple and in range, but
>>>>>>
>>>>>>
>>>>>>            
>>>>>>
>>>>two
>>>>
>>>>
>>>>        
>>>>
>>>>>>things made it a poor choice: it draws about 4.3 mA from the
>>>>>>
>>>>>>
>>>>>>            
>>>>>>
>>>>battery
>>>>
>>>>
>>>>        
>>>>
>>>>>>just for its own supply, and its efficiency when the load is in
>>>>>>
>>>>>>
>>>>>>            
>>>>>>
>>>>the 20-
>>>>
>>>>
>>>>        
>>>>
>>>>>>25 mA range is awful (less than 50%, not counting Iquiescent). I
>>>>>>
>>>>>>
>>>>>>            
>>>>>>
>>>>looked
>>>>
>>>>
>>>>        
>>>>
>>>>>>everywhere but I couldn't find any other switcher with better
>>>>>>performance in these conditions (12V in, 3.3V out, 20-25 mA
>>>>>>
>>>>>>
>>>>>>            
>>>>>>
>>>>average
>>>>
>>>>
>>>>        
>>>>
>>>>>>load, but >1.5A capability). And there's a catch! The radiomodem
>>>>>>
>>>>>>
>>>>>>            
>>>>>>
>>>>is
>>>>
>>>>
>>>>        
>>>>
>>>>>>extremely sensitive to VCC getting lower than 3.3V especially in
>>>>>>
>>>>>>
>>>>>>            
>>>>>>
>>>>the
>>>>
>>>>
>>>>        
>>>>
>>>>>>current peaks! Also, it should be relatively easy to find in ~400
>>>>>>quantities (i.e., Digikey, Mouser or your suggestion).
>>>>>>
>>>>>>
>>>>>>            
>>>>>>
>>>>>I've used the MAX5035 for automotive apps.  Nice part.
>>>>><<http://www.maxim->http://www.maxim->http://www.maxim-
>>>>>
>>>>>
>>>>>          
>>>>>
>>>>ic.com/solutions/automotive/parts.mvp/scpk/1458/pl_pk/0
>>>>
>>>>
>>>>        
>>>>
>>>>>You might consider the MAX5090, it goes up to 2A.  The input
>>>>>
>>>>>
>>>>>          
>>>>>
>>>>voltage range
>>>>
>>>>
>>>>        
>>>>
>>>>>is 6.5V to 72V.
>>>>>
>>>>>Joel
>>>>>
>>>>>
>>>>>
>>>>>          
>>>>>
>>>>
>>>>
>>>>
>>>>SPONSORED LINKS
>>>><<http://groups.yahoo.com/gads?t=ms&k=Microprocessor&w1=Microprocessor&w 
>>>>        
>>>>
>>2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=tsVC-J9hJ5qyXg0WPR0l6g>http://groups.yahoo.com/gads?t=ms&k=Microprocessor&w1=Microprocessor&w2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=tsVC-J9hJ5qyXg0WPR0l6g>Microprocessor 
>>
>>    
>>
>>>><<http://groups.yahoo.com/gads?t=ms&k=Microcontrollers&w1=Microprocessor 
>>>>        
>>>>
>>&w2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=DvJVNqC_pqRTm8Xq01nxwg>http://groups.yahoo.com/gads?t=ms&k=Microcontrollers&w1=Microprocessor&w2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=DvJVNqC_pqRTm8Xq01nxwg>Microcontrollers 
>>
>>    
>>
>>>><<http://groups.yahoo.com/gads?t=ms&k=Pic+microcontrollers&w1=Microproce 
>>>>        
>>>>
>>ssor&w2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=TpkoX4KofDJ7c6LyBvUqVQ>http://groups.yahoo.com/gads?t=ms&k=Pic+microcontrollers&w1=Microprocessor&w2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=TpkoX4KofDJ7c6LyBvUqVQ>Pic 
>>
>>    
>>
>>>>microcontrollers
>>>><<http://groups.yahoo.com/gads?t=ms&k=8051+microprocessor&w1=Microproces 
>>>>        
>>>>
>>sor&w2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=1Ipf1Fjfbd_HVIlekkDP-A>http://groups.yahoo.com/gads?t=ms&k=8051+microprocessor&w1=Microprocessor&w2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=1Ipf1Fjfbd_HVIlekkDP-A>8051 
>>
>>    
>>
>>>>microprocessor
>>>>
>>>>
>>>>----------
>>>>YAHOO! GROUPS LINKS
>>>>
>>>>  *  Visit your group 
>>>>        
>>>>
>>"<<http://groups.yahoo.com/group/lpc2000>http://groups.yahoo.com/group/lpc2000>lpc2000" 
>>
>>    
>>
>>>>on the web.
>>>>  *
>>>>  *  To unsubscribe from this group, send an email to:
>>>>  *
>>>><mailto:lpc2000-unsubscribe@yahoogroups.com?subject=Unsubscribe>lpc2000- 
>>>>        
>>>>
>>unsubscribe@yahoogroups.com
>>    
>>
>>>>  *
>>>>  *  Your use of Yahoo! Groups is subject to the
>>>><<http://docs.yahoo.com/info/terms/>http://docs.yahoo.com/info/terms/>Ya 
>>>>        
>>>>
>>hoo! Terms of Service.
>>    
>>
>>>>----------
>>>>
>>>>
>>>>        
>>>>
>>>
>>>
>>>
>>>Yahoo! Groups Links
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>      
>>>
>>--
>>Tom Walsh - WN3L - Embedded Systems Consultant
>><http://openhardware.net,>http://openhardware.net, http://cyberiansoftware.com
>>"Windows? No thanks, I have work to do..."
>>----------------------------------------------------
>>
>>
>>
>>
>>SPONSORED LINKS
>><http://groups.yahoo.com/gads?t=ms&k=Microprocessor&w1=Microprocessor&w2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=tsVC-J9hJ5qyXg0WPR0l6g>Microprocessor 
>><http://groups.yahoo.com/gads?t=ms&k=Microcontrollers&w1=Microprocessor&w2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=DvJVNqC_pqRTm8Xq01nxwg>Microcontrollers 
>><http://groups.yahoo.com/gads?t=ms&k=Pic+microcontrollers&w1=Microprocessor&w2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=TpkoX4KofDJ7c6LyBvUqVQ>Pic 
>>microcontrollers
>><http://groups.yahoo.com/gads?t=ms&k=8051+microprocessor&w1=Microprocessor&w2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=1Ipf1Fjfbd_HVIlekkDP-A>8051 
>>microprocessor
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-- 
Tom Walsh - WN3L - Embedded Systems Consultant
http://openhardware.net, http://cyberiansoftware.com
"Windows? No thanks, I have work to do..."
----------------------------------------------------

Sean, the device will be idle most of the time. The target 
application will be running ~19 days without recharging from a 12A/H 
12V lead acid battery. Keep in mind that the battery has a self-
discharge ratio that will leave me with ~80% of the charge (9.6 A/H).

My ideal power supply should be extremely efficient in the <100 mA 
range. Due to the duty cycle (>1:60 for four days, >1:600 for 15 
days), I can stand a *linear supply* performance for currents above 
150 mA.

I'm currently experimenting with a MAX1684 for the main circuit (<150 
mA, 100 mA typical when full active) and a linear regulator (LM317) 
for the radiomodem (<5mA typical 98.3% of the time, 160~200mA average 
1.6% of the time). I'm trying to trick the LM317 with large R1-R2 
values (~8KÙ) to keep power consumption low. The radiomodem will work 
well from 3.3 to 4.5V, so I can bear a considerable deal of voltage 
shift in the regulation from this side. Though this may seem a 
nonsense, I'm actually getting better numbers at the end.

Guille

--- In lpc2000@yahoogroups.com, Sean <embeddedrelated@w...> wrote:
>
> Tom:
> 
> I'm confused by your response.
> 
> The datasheet clearly shows that it is possible, it even gives the 
the 
> schematic to do it.  In effect you are building a switching 
regulator, the 
> same way that a premade one works, except with a much lower 
switching 
> frequency.
> 
> I'd imagine that for high loads the efficiency isn't as good as a 
real 
> switching regulator (due to the lower switching frequency), but it 
is much 
> better than linear.  I do not, however, know how well it performs 
with low 
> currents.
> 
> Guillermo:
> 
> What is the duty cycle going to be on your device?  i.e. how much 
time will 
> it spend in idle mode vs low power vs full power mode?  Perhaps 
asking the 
> question a different way:  how much power (in watt-hours say) do 
you expect 
> to use between recharges?
> 
> -- Sean
> 
> At 01:16 AM 12/3/2005, Tom Walsh wrote:
> >Sean wrote:
> >
> > >What type of efficiency does a linear regulator give you when 
setup in a
> > >switching-style topology for low currents?
> > >
> > >
> > >
> >Figure about 30%, maybe %40, efficiency for a linear, three 
terminal
> >regulator.  It is not possible to use a Linear Regulator as a 
switched
> >element...
> >
> >
> >TomW
> >
> >
> >
> > >Check out L7805C datasheet figure 27 in case you don't know what 
I'm
> > >talking about.
> > >
> > >While we're on offtopic, what diodes do you guys recommend using,
> > >especially for lithium backup purposes?  Most diodes that I see 
that are
> > >frequently used have large forward voltage drops for any non-
trivial
> > >current draw.
> > >
> > >-- Sean
> > >
> > >At 12:50 PM 12/2/2005, Guillermo Prandi wrote:
> > >
> > >
> > >>Thanks, Joel. Efficiency on those chips seems still very low 
(around
> > >>50% for my circuit's average load, 15 mA), though the low 
quiescent
> > >>current seems tempting.
> > >>
> > >>Guille
> > >>
> > >>--- In lpc2000@yahoogroups.com, "Joel Winarske" <joelw@i...> 
wrote:
> > >>
> > >>
> > >>>Guille wrote,
> > >>>
> > >>>
> > >>>
> > >>>>Hi! I am in trouble trying to find a voltage regulator 
suitable
> > >>>>
> > >>>>
> > >>for my
> > >>
> > >>
> > >>>>project; my project features an LPC2138, a GPS and a 
radiomodem.
> > >>>>
> > >>>>
> > >>When
> > >>
> > >>
> > >>>>idle, it draws around 20-25 mA from the 3.3V source, 500 mA 
when
> > >>>>working hard and with short (50 mS) peaks of up to 1.8A. The
> > >>>>
> > >>>>
> > >>supply is
> > >>
> > >>
> > >>>>a lead-acid 12V battery (can't change that), and occasionally,
> > >>>>
> > >>>>
> > >>when the
> > >>
> > >>
> > >>>>battery is charging, the input voltage will rise up to ~20V. 
The
> > >>>>problem is the regulator efficiency. We were going for the 
LM2676-
> > >>>>
> > >>>>
> > >>3.3V
> > >>
> > >>
> > >>>>switching regulator, because it seemed simple and in range, 
but
> > >>>>
> > >>>>
> > >>two
> > >>
> > >>
> > >>>>things made it a poor choice: it draws about 4.3 mA from the
> > >>>>
> > >>>>
> > >>battery
> > >>
> > >>
> > >>>>just for its own supply, and its efficiency when the load is 
in
> > >>>>
> > >>>>
> > >>the 20-
> > >>
> > >>
> > >>>>25 mA range is awful (less than 50%, not counting 
Iquiescent). I
> > >>>>
> > >>>>
> > >>looked
> > >>
> > >>
> > >>>>everywhere but I couldn't find any other switcher with better
> > >>>>performance in these conditions (12V in, 3.3V out, 20-25 mA
> > >>>>
> > >>>>
> > >>average
> > >>
> > >>
> > >>>>load, but >1.5A capability). And there's a catch! The 
radiomodem
> > >>>>
> > >>>>
> > >>is
> > >>
> > >>
> > >>>>extremely sensitive to VCC getting lower than 3.3V especially 
in
> > >>>>
> > >>>>
> > >>the
> > >>
> > >>
> > >>>>current peaks! Also, it should be relatively easy to find in 
~400
> > >>>>quantities (i.e., Digikey, Mouser or your suggestion).
> > >>>>
> > >>>>
> > >>>I've used the MAX5035 for automotive apps.  Nice part.
> > >>><<http://www.maxim->http://www.maxim->http://www.maxim-
> > >>>
> > >>>
> > >>ic.com/solutions/automotive/parts.mvp/scpk/1458/pl_pk/0
> > >>
> > >>
> > >>>You might consider the MAX5090, it goes up to 2A.  The input
> > >>>
> > >>>
> > >>voltage range
> > >>
> > >>
> > >>>is 6.5V to 72V.
> > >>>
> > >>>Joel
> > >>>
> > >>>
> > >>>
> > >>
> > >>
> > >>
> > >>
> > >>
> > >>SPONSORED LINKS
> > >><<http://groups.yahoo.com/gads?
t=ms&k=Microprocessor&w1=Microprocessor&w 
> > 
2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor&c=4&
s=93&.sig=tsVC-J9hJ5qyXg0WPR0l6g>http://groups.yahoo.com/gads?
t=ms&k=Microprocessor&w1=Microprocessor&w2=Microcontrollers&w3=Pic+mic
rocontrollers&w4=8051+microprocessor&c=4&s=93&.sig=tsVC-
J9hJ5qyXg0WPR0l6g>Microprocessor 
> >
> > >><<http://groups.yahoo.com/gads?
t=ms&k=Microcontrollers&w1=Microprocessor 
> > 
&w2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor&c=
4&s=93&.sig=DvJVNqC_pqRTm8Xq01nxwg>http://groups.yahoo.com/gads?
t=ms&k=Microcontrollers&w1=Microprocessor&w2=Microcontrollers&w3=Pic+m
icrocontrollers&w4=8051+microprocessor&c=4&s=93&.sig=DvJVNqC_pqRTm8Xq0
1nxwg>Microcontrollers 
> >
> > >><<http://groups.yahoo.com/gads?
t=ms&k=Pic+microcontrollers&w1=Microproce 
> > 
ssor&w2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocesso
r&c=4&s=93&.sig=TpkoX4KofDJ7c6LyBvUqVQ>http://groups.yahoo.com/gads?
t=ms&k=Pic+microcontrollers&w1=Microprocessor&w2=Microcontrollers&w3=P
ic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=TpkoX4KofDJ7c
6LyBvUqVQ>Pic 
> >
> > >>microcontrollers
> > >><<http://groups.yahoo.com/gads?
t=ms&k=8051+microprocessor&w1=Microproces 
> > 
sor&w2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor
&c=4&s=93&.sig=1Ipf1Fjfbd_HVIlekkDP-A>http://groups.yahoo.com/gads?
t=ms&k=8051+microprocessor&w1=Microprocessor&w2=Microcontrollers&w3=Pi
c+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=1Ipf1Fjfbd_HVI
lekkDP-A>8051 
> >
> > >>microprocessor
> > >>
> > >>
> > >>----------
> > >>YAHOO! GROUPS LINKS
> > >>
> > >>   *  Visit your group 
> 
> "<<http://groups.yahoo.com/group/lpc2000>http://groups.yahoo.com/gro
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> >
> > >>on the web.
> > >>   *
> > >>   *  To unsubscribe from this group, send an email to:
> > >>   *
> > >><mailto:lpc2000-unsubscribe@yahoogroups.com?
subject=Unsubscribe>lpc2000- 
> > unsubscribe@yahoogroups.com
> > >>
> > >>   *
> > >>   *  Your use of Yahoo! Groups is subject to the
> > 
>><<http://docs.yahoo.com/info/terms/>http://docs.yahoo.com/info/terms
/>Ya 
> > hoo! Terms of Service.
> > >>
> > >>
> > >>----------
> > >>
> > >>
> > >
> > >
> > >
> > >
> > >
> > >Yahoo! Groups Links
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> >
> >
> >--
> >Tom Walsh - WN3L - Embedded Systems Consultant
> ><http://openhardware.net,>http://openhardware.net, 
http://cyberiansoftware.com
> >"Windows? No thanks, I have work to do..."
> >----------------------------------------------------
> >
> >
> >
> >
> >SPONSORED LINKS
> ><http://groups.yahoo.com/gads?
t=ms&k=Microprocessor&w1=Microprocessor&w2=Microcontrollers&w3=Pic+mic
rocontrollers&w4=8051+microprocessor&c=4&s=93&.sig=tsVC-
J9hJ5qyXg0WPR0l6g>Microprocessor 
> ><http://groups.yahoo.com/gads?
t=ms&k=Microcontrollers&w1=Microprocessor&w2=Microcontrollers&w3=Pic+m
icrocontrollers&w4=8051+microprocessor&c=4&s=93&.sig=DvJVNqC_pqRTm8Xq0
1nxwg>Microcontrollers 
> ><http://groups.yahoo.com/gads?
t=ms&k=Pic+microcontrollers&w1=Microprocessor&w2=Microcontrollers&w3=P
ic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=TpkoX4KofDJ7c
6LyBvUqVQ>Pic 
> >microcontrollers
> ><http://groups.yahoo.com/gads?
t=ms&k=8051+microprocessor&w1=Microprocessor&w2=Microcontrollers&w3=Pi
c+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=1Ipf1Fjfbd_HVI
lekkDP-A>8051 
> >microprocessor
> >
> >
> >----------
> >YAHOO! GROUPS LINKS
> >
> >    *  Visit your 
group "<http://groups.yahoo.com/group/lpc2000>lpc2000" 
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> >    *  Your use of Yahoo! Groups is subject to the 
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> >
> >
> >----------
>

Try this

http://www.romanblack.com/smps.htm

Viktor

viktor_gottschald wrote:

>Try this
>
>http://www.romanblack.com/smps.htm
>
>Viktor
>
>  
>
I think that is cool!  Seems I have some PNP, NPN, couple chokes around 
here...  heh

Thanks for the URL!

TomW

-- 
Tom Walsh - WN3L - Embedded Systems Consultant
http://openhardware.net, http://cyberiansoftware.com
"Windows? No thanks, I have work to do..."
----------------------------------------------------

Thanks, Viktor. I'll check it out. I just must find out the correct 
values for a 3.3V output voltage, and also see how does it perform in 
the low-current scenario.

Guille


--- In lpc2000@yahoogroups.com, "viktor_gottschald" <viktor@b...> wrote:

>
> Try this
> 
> http://www.romanblack.com/smps.htm
> 
> Viktor
>

Sorry, hadn't been following this discussion-- you might be interested 
in this very inexpensive solution: <http://www.romanblack.com/smps.htm>

David

Guillermo Prandi wrote:

> Sean, the device will be idle most of the time. The target
> application will be running ~19 days without recharging from a 12A/H
> 12V lead acid battery. Keep in mind that the battery has a self-
> discharge ratio that will leave me with ~80% of the charge (9.6 A/H).
>
> My ideal power supply should be extremely efficient in the <100 mA
> range. Due to the duty cycle (>1:60 for four days, >1:600 for 15
> days), I can stand a *linear supply* performance for currents above
> 150 mA.
>
> I'm currently experimenting with a MAX1684 for the main circuit (<150
> mA, 100 mA typical when full active) and a linear regulator (LM317)
> for the radiomodem (<5mA typical 98.3% of the time, 160~200mA average
> 1.6% of the time). I'm trying to trick the LM317 with large R1-R2
> values (~8K\ufffd) to keep power consumption low. The radiomodem will work
> well from 3.3 to 4.5V, so I can bear a considerable deal of voltage
> shift in the regulation from this side. Though this may seem a
> nonsense, I'm actually getting better numbers at the end.
>
> Guille

Oops, too late!

David P Harris wrote:

> Sorry, hadn't been following this discussion-- you might be interested
> in this very inexpensive solution: <http://www.romanblack.com/smps.htm>
>
> David
>
> Guillermo Prandi wrote:
>
> > Sean, the device will be idle most of the time. The target
> > application will be running ~19 days without recharging from a 12A/H
> > 12V lead acid battery. Keep in mind that the battery has a self-
> > discharge ratio that will leave me with ~80% of the charge (9.6 A/H).
> >
> > My ideal power supply should be extremely efficient in the <100 mA
> > range. Due to the duty cycle (>1:60 for four days, >1:600 for 15
> > days), I can stand a *linear supply* performance for currents above
> > 150 mA.
> >
> > I'm currently experimenting with a MAX1684 for the main circuit (<150
> > mA, 100 mA typical when full active) and a linear regulator (LM317)
> > for the radiomodem (<5mA typical 98.3% of the time, 160~200mA average
> > 1.6% of the time). I'm trying to trick the LM317 with large R1-R2
> > values (~8K\ufffd) to keep power consumption low. The radiomodem will work
> > well from 3.3 to 4.5V, so I can bear a considerable deal of voltage
> > shift in the regulation from this side. Though this may seem a
> > nonsense, I'm actually getting better numbers at the end.
> >
> > Guille
>
>
>
>
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