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'[EE]: Best way to get +- Supply from Car battery'
2000\08\28@004849 by Damon Hopkins

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I have an application where ideally I'd like to get +18V and -18V
regulated power from a standard car battery (unregulated ~11.5-14+) .. I
can't seem to figure out anything to get me there. The current
requirements are pretty small (certainly less than 50mA probably more
like 10mA) I've tracked down a MAX743 chip that can give me +-15 from a
+6 supply but it costs about $4 in Qty of 1000. I'm not much of a
circuit designer but I can follow one :) so if anyone has any ideas or
suggestions I'd appreciate it.

               Thanks,

                       Damon Hopkins
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2000\08\28@054657 by Oliver Broad

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Not trivial.

Look closely at what you are trying to power first, you seem to be concerned
with cost so can I presume this is a volume application. If this is a 1-off
and you just want it to work then look at buying a DC-DC converter.

If you really want to build your own then work out what power you need and
whether both supplies need full regulation or not. Also decide whether the
demand is spread across both supply rails or whether one supply is trivial
eg <10ma.

Decide whether you are prepared to wind your own transformer.

A simple supply design involves an IC 'Boost Regulator' with a three winding
inductor. Two output windings supply the positive and negative outputs. The
National Semiconductor 'Simple Switcher' design software will design this
type of converter but there are cheaper controller ICs about.

In the sub10mA region I would recomend a charge pump followed by a
conventional regulator, since this is trivial to design.



{Original Message removed}

2000\08\28@083056 by Mike Eggleston

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Oliver Broad wrote:

{Quote hidden}

> {Original Message removed}

2000\08\28@085959 by Thomas C. Sefranek

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Mike Eggleston wrote:

{Quote hidden}

> > {Original Message removed}

2000\08\28@164747 by Lance Allen

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On 28 Aug 2000, at 0:50, Damon Hopkins wrote:

> I have an application where ideally I'd like to get +18V and -18V
> regulated power from a standard car battery (unregulated ~11.5-14+) .. I
> can't seem to figure out anything to get me there. The current
> requirements are pretty small (certainly less than 50mA probably more
> like 10mA) I've tracked down a MAX743 chip that can give me +-15 from a
> +6 supply but it costs about $4 in Qty of 1000. I'm not much of a
> circuit designer but I can follow one :) so if anyone has any ideas or
> suggestions I'd appreciate it.
>

This is a very big subject with an array of options (learnt by
experience... usually making all the wrong choices first off).
It is important to exactly define what you want.
If you want the +/-18 supply for low level audio then a switcher will
need to be high freq (300kHz+...sub-harmonics bite) and then well
post conversion filtered. And yes.. they usually are not cheap.
Maxim have quite a library of engineering examples as do many
other manufacturers.
For the lowest cost, easiest to implement option (in low power apps
like this) I would investigate charge pumps. Double the nominal +12
to around 23 (1 volt lost to diodes) and then linear regulate to +18,
the -ve rail operates off the +23 and is also regulated accordingly.
All you need is a nice  PWM square wave (adjusted for best
efficiency.. i.e. lowest duty cycle that will support the output) and 4
diodes(fast recovery types), 4 capacitors and a +ve 18 regulator
and a -ve 18 volt regulator. If the frequency is say 300kHz to
500kHz the caps can be in the 100s of nanofarads range but the
driver stage from the PWM will need mosfets(one to pull up, one to
pull down) capable a few amps. Beware power mosfets have gate
capacitance of in the low nanofarads, so at 500kHz it will look like a
100 ohms or so to the predriver.
Bulky compared to the nice little Maxim chips and not as efficient but
cheaper.
Check out the myriads of articles, projects and postings on the
subject.

With swithchers the terms cheap, simple, small, low noise and
efficient are somewhat mutually exclusive in most combinations.
_____________________________

Lance Allen
Technical Officer
Uni of Auckland
Psych Dept
New Zealand

http://www.psych.auckland.ac.nz

_____________________________

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2000\08\28@173514 by Gennette, Bruce

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Tell us more about your application - is it completely isolated from the
vehicle?
If so you can use one of these solutions -

2 voltage doublers in series to get 0 to +48V, then create an artificial,
floating 0V somewhere in the middle with 2 large, equal resistors to get
your +-18V.  This is a >$10 solution, most of the cost in 64V capacitors for
the charge pump voltage doublers.

Oliver's suggestion (below) sounds like the right sort of advice.  You
create a chopped AC with a simple oscillator and a power transistor to feed
the input to a custom built centre tapped transformer to get +-24V AC which
you then rectify and regulate.  This is a <$10 solution so long as you wind
your own transformers.

Bye.

       {Original Message removed}

2000\08\28@182732 by David Minkler

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Damon,
Oliver, Lance and the others are right.  Not trivial.  Relatively
straightforward solutions do exist but you do need to determine fairly
closely what you need out of the power supply before you start designing
it.  Minimally, you need to know the range of input voltages (possibly
including noise), the output voltages, output currents, dc regulation,
and tolerance for ripple on the output.  Additionally, you will be
making the obvious tradeoffs between size, cost, efficiency and
complexity.

Personally, I like inductor based switchers (even for the small stuff)
but your requirements seem to be in the range of what is reasonable with
charge pumps.  None of the single chip charge pumps that I am aware of
will operate with either the input voltage range or output voltage range
that you specify so you will have to roll your own.  Without the output
regulation, I would guess you could beat $4 per unit in quantity but you
will have to work for it.

Tell us more about your application.  Perhaps we can do a better job
steering you in the right direction.

Best regards,
Dave Minkler

Damon Hopkins wrote:
{Quote hidden}

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2000\08\28@212024 by Andy Howard

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----- Original Message -----
From: "Damon Hopkins" <EraseMEmdhopkinspam_OUTspamTakeThisOuTUNITY.NCSU.EDU>
To: <PICLISTspamspam_OUTMITVMA.MIT.EDU>
Sent: Monday, August 28, 2000 5:50 AM
Subject: [EE]: Best way to get +- Supply from Car battery


> I have an application where ideally I'd like to get +18V and -18V
> regulated power from a standard car battery (unregulated ~11.5-14+) .. I
> can't seem to figure out anything to get me there. The current
> requirements are pretty small (certainly less than 50mA probably more
> like 10mA) I've tracked down a MAX743 chip that can give me +-15 from a
> +6 supply but it costs about $4 in Qty of 1000. I'm not much of a
> circuit designer but I can follow one :) so if anyone has any ideas or
> suggestions I'd appreciate it.


For around UKP5 (~USD8) (Qty-1 price) you can get a minature 2W encapulated
dual-output DC-DC convertor from Newport Components http://www.dc-dc.com.

I've not seen any 18V ones but they come in quite a variety of input and
output voltages. 5,9,12,15V are values I currently have in the workshop.
They are dual output so you could regulate your car supply down to something
that won't drop out e.g. when cranking the engine and then follow it with
one of these to give both rails. They claim a 2:1 input voltage range but
it's a good idea to put some spike suppression on anything taking car power.

You can buy them from Farnell http://www.farnell.co.uk. According to the website
Mouser also stock them.

I don't see any 18V versions listed but they do say in several places that
they do many custom versions so they may have 18V on the shelf if someone
else has needed it.




















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2000\08\28@213536 by Spehro Pefhany

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At 02:14 AM 8/29/00 +0100, you wrote:

>For around UKP5 (~USD8) (Qty-1 price) you can get a minature 2W encapulated
>dual-output DC-DC convertor from Newport Components http://www.dc-dc.com.

Where did you get that price?

Mouser 1-9 price is USD 21.07
Farnell 1-9 price is GBP 12.77
Their press release states a price of USD 14.37 for >2500 pieces.

I'd love to find DC-DC converters available in small quantities for more
like US$5, I know where to get them in big quantities.

Best regards,


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2000\08\28@221827 by Andy Howard

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----- Original Message -----
From: "Spehro Pefhany" <spamBeGonespeffspamBeGonespamINTERLOG.COM>
To: <TakeThisOuTPICLISTEraseMEspamspam_OUTMITVMA.MIT.EDU>
Sent: Tuesday, August 29, 2000 2:38 AM
Subject: Re: [EE]: Best way to get +- Supply from Car battery


> At 02:14 AM 8/29/00 +0100, you wrote:
>
> >For around UKP5 (~USD8) (Qty-1 price) you can get a minature 2W
encapulated
{Quote hidden}

The one I use most of is Farnell part no. 305-7902 and costs UKP 5.32 in
single quantities (ordered in the UK), 4.75 in 25s and 4.15 in 100s. It's
the 1W part rather than the 2W, but the 2W version is listed here as only
8.21 UKP.

http://www.farnell.co.uk/Search/search-frame1.jhtml?CATID1=24 takes you to
the dc-dc convertors.

http://www.farnell.co.uk/Search/level_5.jhtml?PRODID=25629&SKUID=23614 is
the one mentioned.

Maybe Farnell charge excessively for orders originating outside the UK
(assuming you are outside the UK of course).

Anyway, hope this helps. They're extremely handy little devices and very
small (they take marginally less PCB than an 'F84).

Highly recommended.













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2000\08\28@224551 by Spehro Pefhany

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At 03:10 AM 8/29/00 +0100, you wrote:

>The one I use most of is Farnell part no. 305-7902 and costs UKP 5.32 in
>single quantities (ordered in the UK), 4.75 in 25s and 4.15 in 100s. It's
>the 1W part rather than the 2W, but the 2W version is listed here as only
>8.21 UKP.

Thanks! these ones are not available in 24V input, unfortunately, but the
price agrees with what you gave. Not bad for an *isolated* converter.
The NME and NMA at GBP7.75/7.24 (1W) isn't too too bad.

I was looking at the NDL 2W series (new product), they have a *lot* of
series.

Farnell is actually OK for orders outside UK, I've used them in a pinch
when their local guys (Newark) didn't stock the line. Shipping cost is
a bit more, of course.

Best regards,
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2000\08\28@234307 by Damon Hopkins

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Damon Hopkins wrote:
>
> I have an application where ideally I'd like to get +18V and -18V
> regulated power from a standard car battery (unregulated ~11.5-14+) .. I
> can't seem to figure out anything to get me there. The current
> requirements are pretty small (certainly less than 50mA probably more
> like 10mA) I've tracked down a MAX743 chip that can give me +-15 from a
> +6 supply but it costs about $4 in Qty of 1000. I'm not much of a
> circuit designer but I can follow one :) so if anyone has any ideas or
> suggestions I'd appreciate it.
>
>                 Thanks,
>
>                         Damon Hopkins
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It would be ALOT easier to get +/- 10V regulated wouldn't it?

The application is for a stereo (2 channel) Line driver for a car and
The specs on the parts (the IC's) call for between +-4 to +-18V I'd like
to get as high as possible BUT I don't want to incur unnecessary costs.
10V would be plenty and is found on currently existing devices already.
Probably due to the added costs and design complexity that +-12 or
greater incurs.

a list of IC's if anyone care are Burr Brown OPA2134, DRV134, and
INA134. I can provide a link to the data sheets if needed.

What I want to do is take an unbalanced RCA output (from a head unit),
convert it to a balanced signal (DRV134), run it down a length of cable
,shielded 4 pair twisted (cat 5 cable), and then convert it back to an
unbalanced RCA output jack (INA134). the OPA134 (actually a dual chip
version OPA2134) will be used in there somewhere for basically a gain
setting, probably just before the long cable run. What I envision is a
small case w/ inputs:
2 RCA line inputs (50mv-10v depends on source unit)
1 power wire +12 unregulated from the car power system
1 ground wire (chassis automotive Ground)
1 remote turn on wire (from source unit)

in this case I'd have:
the unit's power supply ( up to +-18V regulated)
the DRV134 chip (the Line Driver chip)
the OPA2134 OP amp to boost the signal for transit down the wire
an output to an 8 position mini-DIN jack

down the wire (8 conductor) I'd like to run
Common Ground
+ system power
- system power
Channel 1 +
Channel 1 -
Channel 2 +
Channel 2 -
remote turn on wire

at the other end another small case with:
a 8 pin mini-DIN connector
the INA134 Chip (unbalancer chip)
and 2 RCA outputs for connections to external amps

right now on parts alone in single quantities my 2 channel line
balancer/unbalancer is $14.20 for the IC's and a few needed capacitors,
no connectors, jacks, power supply, hence my need to keep the costs
down.. I hope to keep the total cost on parts (including case and
connectors) to under $25.

as far as ripple currents on the voltage regulation go.. I'm at a
complete loss.. designing simple fuzz pedals w/ my dad growing up it
didn't come into consideration. :).. shouldn't I be paying for this kind
of help?? j/k don't ask I can't afford it right now :)

               You guys are great,

                       Damon Hopkins
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2000\08\29@051416 by Simon Nield

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As someone else already suggested a charge pump would probably fit the bill here.
Maybe use one element of standard hex cmos inverter as the oscillator and the other five elements
paralleled up through 10 ohm resistors (or whatever) to drive your diode (1n4148  would be fine) /
capacitor networks.
This will give you a rough n* multiplication of the voltage. If you need to regulate that then you
could use a standard 78xx 79xx pair or zeners or just an output capacitor and tweak the
'paralleling' resistors to give you the output you want.

Then again....

I am assuming that the 'long cable run' you are talking about is to an amp at the back of the car
from your head unit ?
and the problem is you get hum / buzz / noise with your current setup so you very sensibly thought
that going balanced would fix it ?
(if not then this won't be much use)

you may be able to solve the problem simply by playing around with the grounding of your system. try
disconnecting the ground wire from the signal cables at one end this might solve your problem
immediately (the noise is actually still there, just a lot less loud)

or even...
don't bother running the circuit at +-18 volts - just use large series caps on the inputs and
outputs of the circuit and run it off 0 and vbat.

Regards,
Simon

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2000\08\29@123908 by Peter L. Peres

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>+/-18V

You can buy intergated hybrid converters that do that. You input 12V +/-
15% and outputs as specified. Try Jameco etc for sources that sell
ones/tens. They will cost more than $4 but you do not need to design
anything ;) +/- 18V is rather hard to get but +/- 15V will be readily
available I think.

Peter

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2000\08\29@154324 by Oliver Broad

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<Really big snip>

>
> Why not just use a 7805? (I'm learning).
>
> Mike
>
Er...

He wanted +/- 18v from the battery, seemed to want a cheap or quick solution
too.

Oliver.

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2000\08\29@154336 by Oliver Broad

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If you can tolerate the reduced swing I think you should try to go single
supply, for Audio it can work very well (for DC applications it is a pain).
Filter your incoming DC with a reasonably high wattage resistor maybe 10 to
100 ohm, then a filter cap. A zener diode could be fitted to protect against
excessive overvoltage. Derive a 1/2 supply reference using a resistor
voltage divider and a large C to ground. Bias your electronics from this so
the audio swings about this point rather than about ground.

At the recieving end you now have a definite proof that the line is
connected which could be valuable, two LEDs to indicate OK or an analog SW
to mute it if open circuit?.



Oliver.



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2000\08\29@165652 by Plunkett, Dennis

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Do not do this, unless you like seeing your prized possession let out the
magic blue smoke (Often known as the silicon genie). The zener diode is not
fast enough to clamp the edge of a load dump situation


Dennis





> {Original Message removed}

2000\08\30@064656 by Andy Howard

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----- Original Message -----
From: "Spehro Pefhany" <spamBeGonespeffSTOPspamspamEraseMEINTERLOG.COM>
To: <KILLspamPICLISTspamBeGonespamMITVMA.MIT.EDU>
Sent: Tuesday, August 29, 2000 3:49 AM
Subject: Re: [EE]: Best way to get +- Supply from Car battery


> At 03:10 AM 8/29/00 +0100, you wrote:
>
> >The one I use most of is Farnell part no. 305-7902 and costs UKP 5.32 in
> >single quantities (ordered in the UK), 4.75 in 25s and 4.15 in 100s. It's
> >the 1W part rather than the 2W, but the 2W version is listed here as only
> >8.21 UKP.
>
> Thanks! these ones are not available in 24V input, unfortunately,


Ah, 24V. If you're looking for a downconvertor then maybe something like
ST's L4962 would do the trick, they're much cheaper too, though not fully
isolated. http://www.st.com/stonline/books/pdf/docs/1357.pdf

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