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'[EE] Regulators in parallel'
2010\12\14@111604 by V G

picon face
Hey all,

I'm having trouble finding LDO linear regulators that can supply > 1 A at 5
V, so I'm thinking of stacking a few 250 mA or 500 mA regulators in
parallel. I want to draw around 1.1 A or so.

Is this a good idea? Is there anything I should watch out for

2010\12\14@112055 by Olin Lathrop

face picon face
V G wrote:
> I'm having trouble finding LDO linear regulators that can supply > 1
> A at 5 V, so I'm thinking of stacking a few 250 mA or 500 mA
> regulators in parallel. I want to draw around 1.1 A or so.
>
> Is this a good idea?

No.  There is no mechanism to guarantee roughly even current sharing.


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

2010\12\14@112619 by Justin Richards

face picon face
>
> Is this a good idea? Is there anything I should watch out for?
> --

I was reading in a magazine that one can parallel up mosfets ok but
not requlators or transistors as they suffer from thermal run away and
don't load share nicely.  I have seen designs that use low value
resistors to help but it is still considered bad design practice.

I think you can use a bypass transistor to increase current handling.

Justi

2010\12\14@112709 by Justin Richards

face picon face
>
> I think you can use a bypass transistor to increase current handling.
>
but then I think you loose the LDO benefits.

Justi

2010\12\14@113848 by alan.b.pearce

face picon face
> > I think you can use a bypass transistor to increase current
handling.
> >
> but then I think you loose the LDO benefits.

And quite frankly, at 1A output current, one would be better off with a
switching regulator.
-- Scanned by iCritical.

2010\12\14@114518 by V G

picon face
On Tue, Dec 14, 2010 at 11:37 AM, <spam_OUTalan.b.pearceTakeThisOuTspamstfc.ac.uk> wrote:

> And quite frankly, at 1A output current, one would be better off with a
> switching regulator.


That's exactly the thing I'm trying to avoid

2010\12\14@115524 by Bob Blick

face
flavicon
face

On Tue, 14 Dec 2010 11:15:48 -0500, "V G" said:
> Hey all,
>
> I'm having trouble finding LDO linear regulators that can supply > 1 A at
> 5
> V, so I'm thinking of stacking a few 250 mA or 500 mA regulators in
> parallel. I want to draw around 1.1 A or so.
>
> Is this a good idea? Is there anything I should watch out for?

Is this for the iPhone charger? If so, I think you can get away with
4-AA nimh cells, a polyswitch fuse, and four resistors(to trigger
charging). At the very least, you need to try it to see if it will
deliver much charge to the phone. Do the test a day after charging the
batteries so they are not at their peak voltage, get out your
multimeter, see if it charges your phone. Then, if the basic idea works,
figure out what is needed to optimize, and add protection as needed.
Don't overbuild it before you have done some actual tests to see what
you really need. This was supposed to be simple.

Cheers,

Bob

P.S. There are some old 1.5 amp LDOs, but they have a fairly high
dropout voltage, too high to be considered really LDO in this day and
age.

-- http://www.fastmail.fm - Does exactly what it says on the tin

2010\12\14@121804 by V G

picon face
On Tue, Dec 14, 2010 at 11:55 AM, Bob Blick <.....bobblickKILLspamspam@spam@ftml.net> wrote:

> Is this for the iPhone charger? If so, I think you can get away with
> 4-AA nimh cells, a polyswitch fuse, and four resistors(to trigger
> charging). At the very least, you need to try it to see if it will
> deliver much charge to the phone. Do the test a day after charging the
> batteries so they are not at their peak voltage, get out your
> multimeter, see if it charges your phone.


I know for sure that the Eneloops can deliver more than 1 A of charge, so
why WOULDN'T it work? I also know what resistor values to use, so the bare
batteries and resistors should work, given that the voltage range is
appropriate.



> Then, if the basic idea works,
> figure out what is needed to optimize, and add protection as needed.
> Don't overbuild it before you have done some actual tests to see what
> you really need. This was supposed to be simple.
>

That's true. But the biggest issue is that I don't know what voltage will
damage the iPhone. The batteries can initially supply 5.8 volts, so that may
be a little too much for the phone to handle

2010\12\14@122219 by David VanHorn

picon face
Just for Grins, Radio shack has a lithium rechargable version of this,
with two USB ports on sale for $20

2010\12\14@124029 by Olin Lathrop

face picon face
V G wrote:
> I know for sure that the Eneloops can deliver more than 1 A of
> charge,

Sure or not, that's still wrong since Amperes is not a unit of charge.
A Ampere is a measure of current, or charge per time, or specifically a
Coulomb per second.


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

2010\12\14@133347 by Bob Blick

face
flavicon
face

On Tue, 14 Dec 2010 12:17:47 -0500, "V G" said:

> > Is this for the iPhone charger? If so, I think you can get away with
> > 4-AA nimh cells, a polyswitch fuse, and four resistors(to trigger
> > charging). At the very least, you need to try it to see if it will
> > deliver much charge to the phone. Do the test a day after charging the
> > batteries so they are not at their peak voltage, get out your
> > multimeter, see if it charges your phone.
>
>
> I know for sure that the Eneloops can deliver more than 1 A of charge, so
> why WOULDN'T it work? I also know what resistor values to use, so the
> bare
> batteries and resistors should work, given that the voltage range is
> appropriate.

The voltage of the batteries under load and as they discharge will
effect how much charge they can actually get to the phone and how much
is left in the batteries. Also, it may be that your phone does something
interesting, like disconnecting, if there isn't enough voltage for 1 amp
to flow.

So I'd have to say that you really don't know it will "work". At least
not satisfactorily. So it makes sense to test the idea.

> That's true. But the biggest issue is that I don't know what voltage will
> damage the iPhone. The batteries can initially supply 5.8 volts, so that
> may
> be a little too much for the phone to handle.

"Initially" is the key, that is why I suggested letting the batteries
sit for a day to relax from their peak voltage. You can also pop them
into a flashlight for a minute or two before your test, just to pull
them down a bit. Remember, I am just suggesting you do a test, not make
this part of a regular process. Do a test in a situation you control.

Of course, what most people would have already done is test with an
adjustable bench supply and the four resistors. And lacking an
adjustable bench supply, gone to Radio Shack, gotten an LM317 adjustable
regulator and potentiometer, and made one. Might come in handy for other
projects.

Cheers,

Bob

P.S. I can pretty much guarantee that you will not be able to get 1 amp
for any length of time if there is anything besides a fuse between the
batteries and the phone. So you will never be able to use an LDO unless
it is so overspec or custom that it is ridiculous. Any method you use to
limit the voltage will need to be a shunt. But 5.8 volts is nothing to
worry about, so you don't even need that.


-- http://www.fastmail.fm - A no graphics, no pop-ups email service

2010\12\14@133715 by Richard Pytelewski

flavicon
face
I have seen a number of circuits that use a small (~0.1 Ohm) resistor on the
outputs to parallel them and handle increased current.  Why not use a
LM123/223/323.  They can supply 3A@5V but they come in a TO-3 or TO-220
case.  
Rich

-----Original Message-----
From: piclist-bouncesspamKILLspammit.edu [.....piclist-bouncesKILLspamspam.....mit.edu] On Behalf Of
V G
Sent: Tuesday, December 14, 2010 11:16 AM
To: PICLIST
Subject: [EE] Regulators in parallel

Hey all,

I'm having trouble finding LDO linear regulators that can supply > 1 A at 5
V, so I'm thinking of stacking a few 250 mA or 500 mA regulators in
parallel. I want to draw around 1.1 A or so.

Is this a good idea? Is there anything I should watch out for

2010\12\14@140020 by V G

picon face
On Tue, Dec 14, 2010 at 12:41 PM, Olin Lathrop <EraseMEolin_piclistspam_OUTspamTakeThisOuTembedinc.com>wrote:

> Sure or not, that's still wrong since Amperes is not a unit of charge.
> A Ampere is a measure of current, or charge per time, or specifically a
> Coulomb per second.


WHOOPS! I meant current. I haven't slept in over 48 hours from exams.
They're finally over

2010\12\14@140233 by V G

picon face
On Tue, Dec 14, 2010 at 1:33 PM, Bob Blick <bobblickspamspam_OUTftml.net> wrote:

{Quote hidden}

You're right. I really need to get myself a bench supply. Ordering one now

2010\12\14@141144 by Michael Watterson

face picon face
On 14/12/2010 17:17, V G wrote:
{Quote hidden}

I doubt that you get that voltage at phone end of cable, with 1A flowing.

Make an approx 5W 5 Ohm dummy load and connect it to batteries via USB socket, cable, usb socket and measure volts at load and volts at battery.

(  20 x 100 Ohm resistors will do)

2010\12\14@143539 by Olin Lathrop

face picon face
V G wrote:
> You're right. I really need to get myself a bench supply. Ordering
> one now.

Surely there must be a bench supply available in a lab in your university
somewhere that you can use when nobody else is trying to use it.


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

2010\12\14@153447 by V G

picon face
On Tue, Dec 14, 2010 at 2:36 PM, Olin Lathrop <KILLspamolin_piclistKILLspamspamembedinc.com>wrote:

> Surely there must be a bench supply available in a lab in your university
> somewhere that you can use when nobody else is trying to use it.


There is, but:

1. I really don't want to be bothering anyone for it. It's far too time
consuming and inconvenient.
2. I'm not part of the faulty of engineering, so the kinds of tools that I
have access to are very different to those that you guys do. I'll need to go
out of my way to access things like bench supplies and stuff.

Just gonna buy one instead

2010\12\14@162555 by RussellMc

face picon face
>...  so why WOULDN'T it work? ...

is very powerful.

But "... why DOESN'T it work .." is often (not always) more powerful.

(Tesla / Shaw / Kennedy versus Edison)

Also often useful is the hybrid.
"Imagine that I tried this and it didn't work. Why might that be?"

In this case you are presenting a device with a falling voltage that
approaches  the maximum charging voltage of  a LiIon cell and then
interposing  some terminals, plugs & socket(s), wiring and known and
somewhat unknown electronics in between source and sink. IF you tried
it and it didn't work as expected it could be because the voltage drop
in the 'stuff' between the two batteries was too high at 1 A to
provide enough voltage for the LiIon cell.

The arithmetic has already been done in prior posts, so this is just
re-noting what has already been  explained. ie it may work well enough
for you, and may not. If it doesn't you should not be at all
surprised.

If you want certain success [tm], then adding a 5th cell and a little
more electronics will make all the difference. Does nasty things to
the battery shape though.

Re LDOs in parallel. As people say - not advisable BUT if they have
thermal and/or over-current graceful linear shutdown they will
probably load share progressively. Not a vastly good idea.


Russel

2010\12\14@172307 by ivp

face picon face
>> And quite frankly, at 1A output current, one would be better off with a
>> switching regulator.
>
> That's exactly the thing I'm trying to avoid.

Why ?

I've been playing around with the ST L6920, MCP1623, MCP1640
boost switchers and MCP1650 (5W, 3V3 - 100V output) boost
controller

http://ww1.microchip.com/downloads/en/DeviceDoc/21876a.pdf

And from Microchip DS22234A

.. Up to 96% Typical Efficiency
.. 800 mA Typical Peak Input Current Limit:
- IOUT > 100 mA @ 1.2V VIN, 3.3V VOUT
- IOUT > 350 mA @ 2.4V VIN, 3.3V VOUT
- IOUT > 350 mA @ 3.3V VIN, 5.0V VOUT
.. Low Start-up Voltage: 0.65V, typical 3.3V VOUT @ 1 mA
.. Low Operating Input Voltage: 0.35V, typical 3.3VOUT @ 1 mA
.. Adjustable Output Voltage Range: 2.0V to 5.5V
.. Maximum Input Voltage < VOUT < 5.5V

They can be paralleled

And there are many boost regulators in more user-friendly packages
that could do the 1A on their own

*
*
**********
Quality PIC programmers
http://www.embedinc.com/products/index.ht

2010\12\14@232406 by V G

picon face
On Tue, Dec 14, 2010 at 5:22 PM, ivp <RemoveMEjoecolquittTakeThisOuTspamclear.net.nz> wrote:

> Why ?
>

How can I boost (1.45 * 4 = ) 5.8 volts to 5 volts? That's why

And in all seriousness, I would need a boost/buck switching supply to
boost/buck 4.4 volts - 5.8 volts to the 5.0 volts that the phone needs. And
boost/buck supplies get complicated to set up. Unless anyone can recommend
me a low part count device that can supply ~1.5A at 5V

2010\12\15@003915 by Spehro Pefhany

picon face
At 11:15 AM 12/14/2010, you wrote:
>Hey all,
>
>I'm having trouble finding LDO linear regulators that can supply > 1 A at 5
>V, so I'm thinking of stacking a few 250 mA or 500 mA regulators in
>parallel. I want to draw around 1.1 A or so.
>
>Is this a good idea? Is there anything I should watch out for?

You could use something like the MIC5157

http://www.micrel.com/_PDF/mic5156.pdf
Typical application on the first page is a 10A LDO.

But 1.1A is not a difficult task for a monolithic part.

Eg. Microchip MCP1827S-5002E/EB  (6V maximum Vin) dropout 0.33V at 1.5A
< $1 in 25's.

Micrel MIC29300-5.0WU (26V max Vin) dropout 0.37V at 3A, 200mV at 1A
< $3 in 25's.

etc.



>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
spamBeGonespeffspamBeGonespaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

2010\12\15@045426 by alan.b.pearce

face picon face
> >> And quite frankly, at 1A output current, one would be better off
with a
> >> switching regulator.
> >
> > That's exactly the thing I'm trying to avoid.
>
> Why ?

My reaction exactly. It seems solarwind is wanting to do things with 3
components when using 5 or 6 results in a much better solution.

Considering that everything for a switching regulator can be got 'off
the shelf' and you don't need to wind bespoke inductors, why shy away
from switchers?
-- Scanned by iCritical.

2010\12\15@055129 by V G

picon face
On Wed, Dec 15, 2010 at 4:48 AM, <TakeThisOuTalan.b.pearceEraseMEspamspam_OUTstfc.ac.uk> wrote:

> My reaction exactly. It seems solarwind is wanting to do things with 3
> components when using 5 or 6 results in a much better solution.
>
> Considering that everything for a switching regulator can be got 'off
> the shelf' and you don't need to wind bespoke inductors, why shy away
> from switchers?
>

Haha. Too late for 3 or 4 components. This thing is becoming bigger than I
intended. I have comparators, FETs, voltage dividers, linear regulators (for
voltage reference), and a switching regulator with all associated components
in my block diagram already

2010\12\15@144754 by Herbert Graf

picon face
On Wed, 2010-12-15 at 05:51 -0500, V G wrote:
> On Wed, Dec 15, 2010 at 4:48 AM, <RemoveMEalan.b.pearcespamTakeThisOuTstfc.ac.uk> wrote:
>
> > My reaction exactly. It seems solarwind is wanting to do things with 3
> > components when using 5 or 6 results in a much better solution.
> >
> > Considering that everything for a switching regulator can be got 'off
> > the shelf' and you don't need to wind bespoke inductors, why shy away
> > from switchers?
> >
>
> Haha. Too late for 3 or 4 components. This thing is becoming bigger than I
> intended. I have comparators, FETs, voltage dividers, linear regulators (for
> voltage reference), and a switching regulator with all associated components
> in my block diagram already.

Use a single cell (or two) boost (i.e. a switcher designed to run off a
single LiIon cell), don't need any of the other stuff then.

TTYL

2010\12\15@145604 by Spehro Pefhany

picon face
At 02:47 PM 15/12/2010, you wrote:
{Quote hidden}

Patient: It hurts when I <...>

Doctor: Don't <...>

>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
EraseMEspeffspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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