Re: Current source design (tricky?)

From: Fred Bloggs (nospam_at_nospam.com)
Date: 03/11/05 

Date: Fri, 11 Mar 2005 12:04:32 GMT

Larry Brasfield wrote:

>
> That helps, but you are still looking at 18 W dissipation under
> "normal" circumstances. (I rely on the 3 Amp output you mentioned in
> your earlier post and battery charging voltage of 16V.) During a
> load dump transient, that could briefly go to 75W. (The transient is
> brief enough that you need not size the heatsink for it, but it may
> mean that you want to keep the junction cooler to provide some
> headroom for the thermal transient.) Whether that can be managed
> with a small heatsink is questionable. I would rely on the heatsink
> vendor's data***.

You are the most worthless pseudo-intellectual p.o.s. on this NG- you
don't even know what a load dump is.

> So, the response to a voltage transient must stay within that bound.
> This makes the design a little more interesting and likely makes it a
> good idea to low pass filter the incoming supply for both the FET and
> op-amp. You will likely want to put a resistor in series with the
> integrator feedback capacitor to improve the transient response of
> the current feedback loop.

Who says the transient response needs "improving"? What circuit are you
referring to?- Certainly nothing posted by you, bull*** boy.

>
> I was not trying to quibble about the meaning of "DC". Ignition
> transients are pretty easy to filter out before they hit the active
> part of your circuit.

That's what you say, mouse, but as usual absolutely no details are
forthcoming.

> The load dump transients change much faster than you appear to
> suspect. You will need to research them.

Isn't that what he's doing now? Why don't /you/ research them and tell
him what they are- what kind of bs non-informational statement is "You
will need to research them"...p.o.s.

> Yes. Maybe.

Hmmm- another highly learned and considered response- what an incredibly
complex mind you have...

> I will not claim these are the most cost effective parts, but they
> will do the job:
> http://ec.irf.com/v6/en/US/adirect/ir?cmd=catProductDetailFrame&produ-
> ctID=IRF9Z24 http://www.national.com/pf/LM/LM8261.html

Both of those parts are unsuitable for this app.

> This op-amp, suggested by Mr. Hill, is well suited for this
> application due to its positive rail input range and capacitive load
> tolerance.

Oh- I'm sure WH was anxiously awaiting your bs approval on that parts
list- what a p.o.s.

>
> Just a few tips for your design:

Oooh- here we go- more bs from the fake:

>
> Be sure to zener protect the op-amp supply. Transients on an
> automobile "12V" rail can be surprisingly large due to quickly
> changing loads,

"suprisingly large"- well what kind of engineering terminology is that,
fruity boy? I don't recall ever seeing "suprisingly" anything in any
data*** specification. What a total p.o.s....

> especially removed loads, and the way alternators are regulated.
> (This effect is often called "load dump".)

Nope- you're wrong about that.

> I would use a 24 or 27 Volt zener diode, grounded at one end.

Really? How much transient power should this generic "zener" be able to
absorb without damage? Or do you intend to sacrifice it at the first blast?

>
> Unless you are willing to see an output current spike sometimes,

"willing"? There you go again with your "girlie man" descriptors. You
think that damned circuit gives a damn about what he's "willing to see"?
What a pathetic little worm joke and incapable piss ant you are!
Unbelievable...

> the MOSFET output stage should get similar protection. I would use a
> power rectifier from the low end of the current sense resistor to
> the zener mentioned above.

A power rectifier?

> You should satisfy yourself that the zener's power rating is
> sufficient to absorb a load dump transient. (I would have to
> research this to know what that might be.)

He should "satisfy himself"- what a waffling p.o.s. moron! And you're damn
right you will have to do some research to find out what that "might"
be...waffling p.o.s.

>
> Your op-amp circuit will be operating with inputs at the positive
> (filtered, protected) rail, and its output is referenced to that rail
> by the feedback condition, so be sure not to ground reference those
> parts of the circuit that influence the controlled current.

More pseudo- theoretical generalistic non-informational PISS. You
haven't provided a stitch of specifics to back a single one of your
bull*** "hints"- friggin wishy-washy pseudo-intellectual worm.

>
>
>> thanks again for the responses!
>
> You're still welcome.

Yeah- right. GFOAD and stay off this NG if that is the kind of weak,
pretentious, non-informational, non-engineering, flake post you offer.