Battery charger - power supply issue affecting ADC

[mister_e]

Weird idea this Zener Z1 so far...

But yeah i'll second the PWM idea.. maybe just remove the LM317 as well and use a Mosfet/Transistor instead and do everything in software. a 12F683 would be perfect for that.

1 current senses
1 voltage sense
1 PWM and
remaining pins for leds and maybe other safety inputs.

[inse]

Hello Roger,

one thing I have noticed in your schematic: do you have a ground connection on the OPAMP?
It's ground pin (4) seems to be floating...

Regards,

Ingo

[flotulopex]

Thank you Ingo,

Good observation!

I corrected the schema and the circuit (I was already noticed about this by Acetronis some hours ago - as I say, better two times than never ).

Weird idea this Zener Z1 so far...

As I'm not an electronician but a real "bricoleur du dimanche". Anyway, why is the use of a Zener this way not a good idea?

Ioannis, your math is absolutely correct but when I take my FLUKE87 or my scope, they both show a maximum of 3,45 volts. This has to be, again, one of this famous frontier between theory and real life .

I forgot to ask: what type/model of MOSFET or Transistor would fit my application best please?

[Ioannis]

Your current is up to 1,2A so any transistor that can handle the double to be safe, could be used. TIP31 (3A) or MJE3055 (10A) are a few examples.

The idea is to design a simple classic linear power supply that would be controlled by your PIC about the voltage and current. That would require A/D converters but to be very fast, a good designed Sigma-Delta converter may have to be used instead off the classic ADC's.

That's what is hidden in the Elektor's article I mentioned.

Ioannis

[flotulopex]

I'm searching for this ELEKTOR info - but seems to be available only for members... Still looking for it.

Using PWM, I will generate a voltage variation. If I'm right, a MOSFET can be "voltage" controlled; this is not true for a transistor.

I assume it will be better to use a MOSFET, no?

[Acetronics2]

I'm searching for this ELEKTOR info - but seems to be available only for members... Still looking for it.


I assume it will be better to use a MOSFET, no?

Hi, Roger

Here : http://www.elektor.fr/magazines/2001...1).65895.lynkx

a P mosfet will be easy to use ... a N Mosfet a bit harder ...

But there's some more investigation to do with your circuit before throwing it to the wastebox ...

Alain

[Ioannis]

I repeat again that, your final design might look like a Linear Power Supply.

As such, a NPN pass transistor is the usual choice. The transistor acts like a voltage follower, so whatever voltage is present at the base, that voltage-0,7 is presented at the emitter, with current amplification of course.

Ioannis

[Acetronics2]

Ioannis, your math is absolutely correct but when I take my FLUKE87 or my scope, they both show a maximum of 3,45 volts. This has to be, again, one of this famous frontier between theory and real life .

?

Hi,

IF we consider The 317 has a max ref voltage and a max Iadj current ... those readings are possible ... ( your 317 is "not so good" , Roger !!! )
But that also mean ANOTHER 317 could damage the DS 1804 ...

this design won't be good for series production ...

Now, Roger, there's another point to verify ... your PCB tracks !!! are they sufficient to hold the required current ...
And overall ... did you use a "star" config to link your ground tracks ???
( maximum care for R5 ground return path ...)

Alain

[Acetronics2]

Weird idea this Zener Z1 so far...

But yeah i'll second the PWM idea.. maybe just remove the LM317 as well and use a Mosfet/Transistor instead and do everything in software. a 12F683 would be perfect for that.

1 current senses
1 voltage sense
1 PWM and
remaining pins for leds and maybe other safety inputs.

Hi,

I didn't remember it at first ... but the 317 can be used as a "switching transistor" for PWM !!! ... just do not use too high a PWM frequency and it will work rather pretty ...

YES ... the "off" state voltage will be 1.25 v ... but, here, no issue with that !!!

do not laugh ! ... I have the proof ... it was ... 18 years ago, for a model train controller !!!

Alain

[Ioannis]

Very nice! State-of-the-art design! PWM with 1,25 offset!

I'd like to have one! He, he.

By the way have a look at the LM2576T-ADJ chip that is a 3A switcher.

Very cheap and very easy! And adjustable too!

Ioannis

[Acetronics2]

Very nice! State-of-the-art design! PWM with 1,25 offset!


Ioannis

Hi,hi ...

no problem here ... due the batt !!! the BY 500 will be reverse polarized during 1.25v level ...so, no current flowing ...

CQFD !

I can mail you a copy of the scheme ... just ask !


Alain

[Ioannis]

I can mail you a copy of the scheme ... just ask !

Yeah, why not. Always collecting ideas!

Ioannis

[Acetronics2]

Yeah, why not. Always collecting ideas!

Ioannis

So, just have a look to LM317 datasheet ... NS gives 2 examples of 317 based switching regulators page 17 ...

some kind of humour ... isn't it ???

Alain

[Ioannis]

He,he. Alain, the great!

Ioannis