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'[EE]: PIC in an automotive circuit/voltage regulat'
2003\01\07@010353 by Rodrigo Valladares P.

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Hi All,

i'm developing a pic based automotive electronic ignition, it's based on
a mc10012 darlington as the main coil switch, a very low value
resistance for current feedback/sensing and a pic for controlling the
dwell angle at various rpm. in paper and in my desk works well, but i
think that the voltage regulator must be a little more than a 7805, so,
where i can find information (or schematics) for build a reliable
voltage regulator?, and what precautions i must follow to minimize
noise, etc? (it's for a jeep, and i don't want the motor to stall
climbing a hill)

any help will be great!

thanks

RVP.

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2003\01\07@012750 by Rodrigo Valladares P.

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This was forgotten from the original message:

i know that i must use a low dropout voltage regulator for automotive
applications (i have a couple of lm2940 for this project), i'm worry
about others components (capacitors, inductances, zenners, etc) that
will help to keep noise away from the pic. remember that in the other
side of the pic i have a hv coil, with one terminal on the 12v of the
battery.

thanks again.

RVP.

Rodrigo Valladares P. wrote:

{Quote hidden}

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2003\01\07@101021 by Howard McGinnis

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Have you considered the 16HV540? It shouldn't need the regulator, however
it's not a flash part and lacks EE.

Howard

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2003\01\07@102854 by Larry Bradley

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I use the National LM2931 series of low dropout voltage regulators in
marine engine applications. There is an adjustable version, plus a 5 volt
foxed version. These are designed for automotive applications, where
transient voltages on the battery can be quite high. Check it out in the
National Semi web site

http://www.national.com/design/index.html


As to noise - filter, filter, filter. Use an RC filter on all inputs from
sensors - the values will depend on the expected rate-of-change of the
sensor data. I tend to use a 1K resistor and a 10uf capacitor with a 0.1 uf
capacitor in parallel on all input signals in "slowly changing" systems.
Tie all unused inputs to ground.

Use a filter on the 12V input (before the regulator) to help keep noise out
of the power supply.

Don't use the automotive ground for sensor return if you can help it. For
example, if you have a series resistor (shunt) to measure current, use a
4-wire connection for the shunt - connect it in the circuit to be measured
with the normal leads, then connect two more wires to the resistor closer
to the resistor body than the normal leads to use as your sensor wires.
Then use an opamp in a differential configuration connected to the sense
wires (if you need more info on this get back to me) to help eliminate
noise on the sensor wires.

Use a separate wire for the emitter of the switching transistor - don't
just use the negative supply line to your PIC circuit. Connect this wire to
ground at the engine block, or some such ground point. You don't want the
switching current going through the negative supply line to the PIC - nasty
spikes. I'd even be tempted to mount the switching transistor close to the
coil, rather than as a part of the PIC circuitry, and just
feed the base drive voltage to it from the PIC - again, with a filter on
this lead - the filter values probably need to be smaller than 1k/10uf
since the filter will effect the rise time of the switching pulse.

And you might think about building it in a metal box, rather than a plastic
one.

Have fun!

Larry

At 02:56 AM 1/7/2003 -0400, you wrote:
{Quote hidden}

Larry Bradley

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Orleans (Ottawa), Ontario, CANADA

2003\01\07@231107 by Rodrigo Valladares P.

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Hi,

i have to deal with small stores of electronic components, so i don't
have access to all the pic micro family, do you know how well this
device will be in an hostile environment?

thanks

Howard McGinnis wrote:

> Have you considered the 16HV540? It shouldn't need the regulator, however
> it's not a flash part and lacks EE.
>
> Howard
>
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>

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2003\01\07@231525 by Rodrigo Valladares P.

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thanks larry, i will follow word by word all your advice, really lots of
fun awaits me

RVP.


Larry Bradley wrote:

{Quote hidden}

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2003\01\08@133127 by Howard McGinnis

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To be honest, I don't know. I bought some JW versions as well as some OTP's
for an automotive product, but didn't get around to doing anything yet. I
think they were designed with automotive functions in mind, but don't know
for sure!

Howard


At 01:07 AM 1/8/2003 -0400, you wrote:
{Quote hidden}

Howard McGinnis
Electronic Visions, Inc.
spam_OUTmcginnisTakeThisOuTspame-visions.com
http://www.e-visions.com

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2003\01\08@162655 by Spehro Pefhany

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At 01:31 PM 1/8/03 -0500, you wrote:
>To be honest, I don't know. I bought some JW versions as well as some OTP's
>for an automotive product, but didn't get around to doing anything yet. I
>think they were designed with automotive functions in mind, but don't know
>for sure!

They seem to have been, but they also seem to be orphaned chips, with only
a single member in the family, like the PIC14000.

Automotive supplies have a lot of nasty transients, check the relevant
standards for the exact requirements, but +/-24V 5 minutes jump start,
and 125V 200-500ms 10J load dump, and the 300V-80V 1J 320usec inductive
transients, -100V 1J alternator field decay etc (at each shut off), etc.
I think the standards are something like ISO 7637 and SAE J1113.

It's not hard to meet them if your circuit just draws a bit of current,
you just put lots of series impedance and a hefty shunt zener or TVS
in there. Some regulators like the LM2940 have *some* protection built-in
but be careful about the output capacitor, they are only stable for
some values and some ESRs. If your cap is too big, too lousy, too small
or too *good* you get an oscillator.

Best regards,

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

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2003\01\08@172141 by Larry Bradley

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The LM2941 series are designed as automotive regulators - they handle
reverse polarity, load dump - take a look at the National web site.

I've been using one in a PIC-based circuit on my sailboat which has an
ancient old gasoline engine - so far so good. It too is a low-dropout
regulator, requiring a hefty low ESR (read tantalum) capacitor - they
recommend 47uf or more - I use 2x47 uf tantalum in parallel.

Larry

At 04:26 PM 1/8/2003 -0500, you wrote:
{Quote hidden}

Larry Bradley
Orleans (Ottawa), Ontario, CANADA

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