Searching \ for '[EE] protecting a battery charging IC from overvol' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: techref.massmind.org/techref/power/batterys.htm?key=battery
Search entire site for: 'protecting a battery charging IC from overvol'.

Exact match. Not showing close matches.
PICList Thread
'[EE] protecting a battery charging IC from overvol'
2006\07\30@022434 by Anon

picon face
I am using a Maxim battery charging chip that accepts 2 DC inputs.
 www.maxim-ic.com/quick_view2.cfm/qv_pk/4002
 The DC inputs are limited to 7V. My assumption is that a higher voltage could damage the IC. One of the inputs comes directly from a connected USB port. The other input will come from a DC wall adapter. My design is a consumer electronics device. There is a potential that someone may connect a DC adapter with a voltage that exceeds 7v.
 Is there some way I can protect the input from overvoltage? I though about a 7V 2W zener diode, however its knee (trigger point) may not be sharp enough to absorb an overvoltage condition. Thanks
 
 
 
 

               
---------------------------------
How low will we go? Check out Yahoo! Messenger’s low  PC-to-Phone call rates.

2006\07\30@025519 by Bob Axtell

face picon face
Anon wrote:
> I am using a Maxim battery charging chip that accepts 2 DC inputs.
>   www.maxim-ic.com/quick_view2.cfm/qv_pk/4002
>   The DC inputs are limited to 7V. My assumption is that a higher voltage could damage the IC. One of the inputs comes directly from a connected USB port. The other input will come from a DC wall adapter. My design is a consumer electronics device. There is a potential that someone may connect a DC adapter with a voltage that exceeds 7v.
>   Is there some way I can protect the input from overvoltage? I though about a 7V 2W zener diode, however its knee (trigger point) may not be sharp enough to absorb an overvoltage condition. Thanks
>    
>    
>    
>    
>
>                  
> ---------------------------------
> How low will we go? Check out Yahoo! Messenger’s low  PC-to-Phone call rates.
>  
Incredible. This chip is a non-starter. Its a non-starter because it
requires 7V DC or less. In my 30+ years
of designing products, I've NEVER seen a wallwart that delivered less
than 7V (I'm sure they are there, but
I've never seen any. Your prospective purchasers won't be able to find
them either.) So, you will need to
build in a bunch of protective devices, zeners, preregulators etc; its
now a mess.

What you need to do is design this one out, and start over with a
slightly more expensive chip that actually
will do something useful. There are several by LT. Most handle DC inputs
to 16V as well as the USB source.
That also will then allow you to charge the battery while driving (thru
the cigarette lighter), a great convenience
to commuters. Some are switchers, which will eliminate charging heat as
well.

You have to watch Maxim. They've done this several times before.

--Bob

2006\07\30@032954 by Tony Smith

picon face

> Anon wrote:
> > I am using a Maxim battery charging chip that accepts 2 DC inputs.
> >   www.maxim-ic.com/quick_view2.cfm/qv_pk/4002
> >   The DC inputs are limited to 7V. My assumption is that a
> higher voltage could damage the IC. One of the inputs comes
> directly from a connected USB port. The other input will come
> from a DC wall adapter. My design is a consumer electronics
> >  
> >
> Incredible. This chip is a non-starter. Its a non-starter
> because it requires 7V DC or less. In my 30+ years of
> designing products, I've NEVER seen a wallwart that delivered
> less than 7V (I'm sure they are there, but I've never seen
> any. Your prospective purchasers won't be able to find them
> either.) So, you will need to build in a bunch of protective
> devices, zeners, preregulators etc; its now a mess.


They exist, and they're becoming more common.  I've got a few odd-ball wall
warts, 2.5v, 3v, 4.5v that power dictaphones, walkmans, portable CD players
etc, mainly stuff that used 2xAA batteries.  Low amps, these usually didn't
recharge the device.

These days a lot of PDAs, cameras, iPods, phones and the like have a ~5v
wallwart, since they are often powered & recharged off the USB port.

Those 'selectable voltage' ones do 3v, 5v etc as well, provided you remember
to check it.

Still, doesn't solve the problem of plugging in a 12v one instead.  Would
have been nice if the size/type of the plug determined the voltage, but it's
hard enough getting everyone to to get the polarity right (yes, that's you,
Sony).

Tony

2006\07\30@055012 by Bob Axtell

face picon face
Tony Smith wrote:
{Quote hidden}

But the chip will not be able to tolerate ANY voltage above 7V. Think
about it. Even a surge can drive a
5V unreg wallwart about 7V. Those selectable voltage ones are
unregulated, and the "5v" selection is over
7V. Try it.

No, its a non-starter.

--Bob


2006\07\30@060634 by William Chops Westfield

face picon face

On Jul 29, 2006, at 11:55 PM, Bob Axtell wrote:

> In my 30+ years of designing products, I've NEVER seen a
> wallwart that delivered less than 7V...

I think ALL of the wall-warts that charge cell phones are
less than 7V, designed in general to charge 3.6V batteries.
My Nokia charger says 3.7V; I assume that's "nominal"...

So I would not be surprised to find any chip aimed specifically
at the cellphone space to max out at lower than expected
voltages...

BillW

2006\07\30@063252 by Tony Smith

picon face
{Quote hidden}

A lot of the newer ones are switchmode, well regulated, high amp and low
weight as a bonus.  Nokia phone chargers certainly are, and in front of me I
have one for a USB hub, 5v 3.75A.  Quite impressive compared to the old
transformer / 4 diodes / capacitor versions you're talking about.

Most electronics will get upset by 7v anyway, look at 3v memory chips.  Few
things are going to survive someone plugging an old Netcomm modem
transformer (15v AC nominal) into it.  Most people seem to 'solve' the
problem by designed a special plug for the power.

Tony

2006\07\30@071316 by mail.deamon

picon face
Tony Smith schrieb:

{Quote hidden}

if you try an step up converter like lm2988,
or use buck converter with double conversion?

killaweb

2006\07\30@072133 by Bob Axtell

face picon face
Tony Smith wrote:
{Quote hidden}

I agree. The special plug is the fix. Good catch.

--Bob

2006\07\30@142332 by David VanHorn

picon face
>
>
> You have to watch Maxim. They've done this several times before.


Other than the MAX232 (Which I get from Nat Semi for much less), I really
try hard to avoid the dallas/maxim mess. So many reasons.. :-P

2006\07\31@040015 by Russell McMahon

face
flavicon
face
>>... In my 30+ years of designing products, I've NEVER seen a
>>wallwart that delivered
>> less than 7V (I'm sure they are there, but I've never seen
>> any.

> They exist, and they're becoming more common.  I've got a few
> odd-ball wall
> warts, 2.5v, 3v, 4.5v that power dictaphones, walkmans, portable CD
> players
> etc, mainly stuff that used 2xAA batteries.  Low amps, these usually
> didn't
> recharge the device.

As a general but reasonably adhered to rule, unregulated supplies will
have outputs up to around 40% above rated voltage on light loads and
regulated supplies will have voltages about as specified. "Regulated"
includes linear regulated supplies and switchers. The switchers MAY
have much higher voltages on low load but tend to be less severe in
variation than unregulated "iron cored" supplies.

In your application, Bob's suggestion to quit while ahead and use
another part is probably the best one. However:

Depending on other factors it MAY be worthwhile using a switching
power supply that meets your input spec BUT probably not.

An iron transformer based unregulated supply more or less has to have
its unloaded input rise to substantially higher than when loaded due
to the 1.414 ratio between peak voltage and RMS voltage. The actual
ratio will vary with diodes used, filter capacitors, spreading
resistors (seldom seen), filter inductor(s) (nowadays seldom seen),
transformer resistance and more.  Even partial core saturation under
heavy load (when designed 'to the limit') can increase voltage
variation. (And
technology-indistinguishable-from-magic-due-to-modern-rarity saturable
inductor regulators can reduce variation to almost zero).

In days of old where people were desperate to limit both voltage
variation and cost an SCR preregulator was sometimes used, and a FET
based system would nowadays be about as cheap. But it is most unlikely
that you would want to use such a system.

A simple and cheapish and moderately effective system would be the use
of a simple series preregulator using a zener and, a pass transistor
and another control transistor plus a very few glue parts. This can be
cheap and reasonably effective.

.

       Russell McMahon

2006\07\31@041139 by Alan B. Pearce

face picon face
>In my 30+ years of designing products, I've NEVER seen
>a wallwart that delivered less than 7V (I'm sure they
>are there, but I've never seen any. Your prospective
>purchasers won't be able to find them either.)

Some of the cell phone ones do about 3.5V - and it sounds like this Maxim
chip is designed for use in cellphones.

2006\07\31@041520 by Alan B. Pearce

face picon face
>Would have been nice if the size/type of the plug determined
>the voltage, but it's hard enough getting everyone to to get
>the polarity right (yes, that's you, Sony).

The example I know of was a Sharp laptop and LCD display for putting on an
overhead projector. The two devices from the same manufacturer had identical
looking power supply blocks - with the opposite polarities set on the plugs.
One day just before a very important presentation the inevitable happened -
and both devices went poof.

2006\07\31@041728 by Alan B. Pearce

face picon face
>But the chip will not be able to tolerate ANY voltage
>above 7V. Think about it. Even a surge can drive a
>5V unreg wallwart about 7V. Those selectable voltage
>ones are unregulated, and the "5v" selection is over
>7V. Try it.
>
>No, its a non-starter.

But most of the low voltage wall warts I have come across use a switching
supply - very viable in this application, which mean they have a stable
output voltage.

2006\07\31@043914 by Tony Smith

picon face

{Quote hidden}

Nah, "Warranty void if non-approved power supply used" sticker - how much
are they?  :-)

Tony

2006\07\31@145604 by William Chops Westfield

face picon face
On Jul 31, 2006, at 1:39 AM, Tony Smith wrote:

> Warranty void if non-approved power supply used" sticker...
>
My respect for a manufacturer always goes up a notch if the
wall wart has a sticker identifying which product it attaches
to.  Or even the main manufacturer's name.  WAY too many products
come with an anonymous OEM wall wart that looks like all the other
anonymous OEM wall warts...

BillW

2006\07\31@152535 by Marcel duchamp

picon face
William Chops Westfield wrote:
> On Jul 31, 2006, at 1:39 AM, Tony Smith wrote:
>
>> Warranty void if non-approved power supply used" sticker...
>>
> My respect for a manufacturer always goes up a notch if the
> wall wart has a sticker identifying which product it attaches
> to.  Or even the main manufacturer's name.  WAY too many products
> come with an anonymous OEM wall wart that looks like all the other
> anonymous OEM wall warts...
>
> BillW

I agree.

But until they do, I have found a good use for business cards. I write
the product the wall wart goes to on the back of the card and then fold
it length-wise and pass the cord through it.  Then staple the card edges
together to keep it in place.  A bit kludgey but it works for me.

Besides, what else am I going to do with business cards?


'[EE] protecting a battery charging IC from overvol'
2006\08\01@003217 by Tony Smith
picon face
> > Warranty void if non-approved power supply used" sticker...
> >
> My respect for a manufacturer always goes up a notch if the
> wall wart has a sticker identifying which product it attaches
> to.  Or even the main manufacturer's name.  WAY too many
> products come with an anonymous OEM wall wart that looks like
> all the other anonymous OEM wall warts...


Most of the Japanese manufacturers label their with their brand name, but
that's not much of help, unless you only own one Sony or Panasonic item.  I
can't recall anyone labelling the plugpack with the product it's for.

I just put a tag next the plug.  Product / volts / amps / polarity if I'm
enthusiatic enough, or if it's non-standard.  I have a Palm PDA transformer
here, the black box has a generic Chinese manufacturer, the plug has a
sticker with the Palm logo and the 'warranty void...' message.

Switchmode, 5.5v & 0.35A, weight 116g.  In a few years this type will start
to outnumber the old iron core one in my junk box.

Tony

More... (looser matching)
- Last day of these posts
- In 2006 , 2007 only
- Today
- New search...