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'[EE]: Digital current selector'
2002\02\23@065911 by Diego Sierra

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face
Hi!

Can someone give a me a hint or url on how to digitally select a current.

What I want is a PIC to control a current with its output pins. For
instance, with output 00 = 1A, 01 = 750mA, 10 = 500mA, 11 = 250mA.

Thanks in advance,
Diego.

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2002\02\23@081738 by Thomas C. Sefranek

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Over what voltage compliance range?
What control voltage burden have you allowed?

Current is controlled with series resistance.

Therefore, if can control the resistance of a circuit you inherently
control the current.

Diego Sierra wrote:

{Quote hidden}

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2002\02\23@090852 by Diego Sierra

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On Sat, 23 Feb 2002, Thomas C. Sefranek wrote:

> Over what voltage compliance range?
> What control voltage burden have you allowed?

The output voltage should be between 2V and 15V, then input voltage is
about 18V.

I will be happy with just an idea on how to do it.

> Current is controlled with series resistance.

Ok, I see that, using a regulator such a lm317 I can have a constant
current, changing the resistance connected to it I can change the current
value; and now the question arise: who to attach the outputs pins of the
pic to change that resistance value?

Cheers,
Diego.

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2002\02\23@094354 by Thomas C. Sefranek

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Diego Sierra wrote:

>On Sat, 23 Feb 2002, Thomas C. Sefranek wrote:
>
>>Over what voltage compliance range?
>>What control voltage burden have you allowed?
>>
>
>The output voltage should be between 2V and 15V, then input voltage is
>about 18V.
>
>I will be happy with just an idea on how to do it.
>
>>Current is controlled with series resistance.
>>
>
>Ok, I see that, using a regulator such a lm317 I can have a constant
>current, changing the resistance connected to it I can change the current
>value; and now the question arise: who to attach the outputs pins of the
>pic to change that resistance value?
>
What granularity do you need?
For just a few values you can do a pseudo D-A with resistors.
Otherwise a "real" D to A is good for this.

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2002\02\23@145449 by uter van ooijen & floortje hanneman

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> What I want is a PIC to control a current with its output pins. For
> instance, with output 00 = 1A, 01 = 750mA, 10 = 500mA, 11 = 250mA.

You might get a better answer when you give some more information about what
you really want. Probably PWM is a solution?

Wouter van Ooijen
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2002\02\23@181200 by Olin Lathrop

face picon face
> Ok, I see that, using a regulator such a lm317 I can have a constant
> current, changing the resistance connected to it I can change the current
> value; and now the question arise: who to attach the outputs pins of the
> pic to change that resistance value?

You can use two pins to a 2 bit D/A made from resistors to get the four
voltage levels, then use these to drive a current source.  You could also
use a single PIC output pin with PWM.


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2002\02\23@200733 by Diego Sierra

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Hi!

> You can use two pins to a 2 bit D/A made from resistors to get the four
> voltage levels, then use these to drive a current source.  You could also
> use a single PIC output pin with PWM.

Thanks!. Sure that PWM is a solution, as Wouter said, but I was looking
for that D/A idea.

Cheers,
Diego.

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2002\02\25@093317 by kben

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<SNIP>
You could also
use a single PIC output pin with PWM.
<SNIP>
This sounds like a good way to make a
NiMH PWM battery charger.  What frequency
should the PWM be at to control the LM317.
Anyone care to describe a simple control circuit
for a F628 and a LM317 ? I am not sure how I would
control the LM317 with the PWM pin from the PIC.
I have eight 1500Mah AA's, for a 9.6v battery
pack and was looking into designing a smart charger
for a PIC.

TIA,
Kevin

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'[EE]: Digital current selector'
2002\03\04@044945 by Diego Sierra
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"Kevin A. Benedict" wrote:

> I have eight 1500Mah AA's, for a 9.6v battery pack and was looking
> into designing a smart charger

Hi Kevin,

have a look at this (someone posted it on the list some time ago):

http://www.angelfire.com/electronic/hayles/charge1.html

And this one is interesting also, on nicad chargers:

http://www.pstec.de/ppp/pppaccu/pppaccu.html

Cheers,
Diego.

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