
The LM383 Story - ksikka
http://www.idea2ic.com/LM383/index.html
======
phkahler
Load dump is not about connecting two batteries in series to achieve 24V. It's
about (accidentally?) disconnecting the battery while charging from the
alternator - which is an inductive source. When the load taking the current is
disconnected that current is going to continue flowing through the vehicle
electrical system which will cause a voltage spike until the current goes
down.

On a related note, I heard this 2nd hand from a guy who was talking to CAT
about a module they wanted to have 80V over voltage protection for a crazy
amount of time (minutes). My friend asked what scenario required that and it
was something like this: Guy at a construction site can't start his bulldozer.
He doesn't have jumper cables, but he's got an arc welder... I don't know if
that actually happened but it would not surprise me.

~~~
CamperBob2
Yes, that was a weird mistake for someone in the author's position to make.

That said, I may not understand what a 'load dump' condition is, myself -- I
always thought it referred to the common case where a high current load is
switched off abruptly, causing the voltage to spike until the alternator's
regulator circuit can respond by reducing the field coil current.

Disconnecting the battery would not be expected to cause such a condition,
since the charging current is not all that high most of the time compared to
other loads. I wouldn't expect much of anything to happen when disconnecting
the battery from a running car. It should just keep running.

~~~
neuralRiot
In old cars it was a quick test to see if the alternator was working so some
people still think that this is a good idea, IT IS NOT! newer alternators are
controlled via LIN bus by the BCM so to generate more current when needed not
just using battery voltage as a reference, if you disconnect the battery the
voltage can go up to 30v even a bad battery or one with very low charge can
make the charging system either shut off or go nuts.

------
nicolaslem
I have great memories building small guitar amplifiers out of its little
brother the LM386.

Adding just a transistor to handle the high impedance of the guitar and a few
cents worth of resistors and capacitors, one could build a tiny amplifier that
once plugged to a 12" guitar speaker could make some serious rock'n'roll!

I remember taking most design ideas from this gold mine: [https://www.sonelec-
musique.com/electronique_realisations.ht...](https://www.sonelec-
musique.com/electronique_realisations.html) (unfortunately only in French)

~~~
frabert
It's widely known ad the "noisy cricket" amp I believe :)

------
weinzierl
This is a fantastic read. At the risk of being the guy that needs the joke
explained, I can't make sense of following paragraph:

> _While the -6 volt supply spec caused little trouble for the LM383, it meant
> that all the other electronics in a car needed to voltage regulator that
> could provide protection._

The other components need protection anyway. What is the connection to the
LM383?

> _Some one made the joke that the lateral PNP 's were so bad that even delco
> would not be able to destroy them._

Why are bad lateral PNP's hard to destroy? Is he talking about PNP's inside
the LM383 or inside other power supply circuitry that's supposed to provide
protection?

> _A skunk works layout of a lateral PNP regulator ultimately made its way to
> delco. And sure enough, they could not destroy it. They loved it. And
> National Semiconductor got into the business of making PNP output
> regulators._

~~~
jjoonathan
I think the -6V connection was simply that the LM383 designers were able to
trivially integrate something the automotive industry considered non-trivial
due to historical reliance on discrete processes and "build it sturdy"
engineering. Nowadays chips are so highly integrated, so cheap, and so
ubiquitous that it's hard to imagine dealing with messy power any other way,
but it wasn't always so.

I have vague intuition that p-type silicon has lower mobility and worse ohmic-
junction performance than n-type silicon. A real semiconductor engineer should
verify, but I believe the core of the dig is that the low performance acts
like intrinsic protection: the PNPs simply couldn't conduct enough current to
destroy themselves, at least not in the multitude of spectacular fashions as
the NPNs.

~~~
mbell
Electrons are the majority charge carriers for NPN vs holes in PNP which does
mean that NPN transistors are faster, they also are usually a _bit_ better
than PNP in other specs (beta, etc).

However I don't think this was the main part of the joke, rather it's that
lateral transistors are _way_ worse in pretty much every conceivable metric
than vertical transistors save two - they are hard to destroy and cheap. So
add 'lateral' to 'PNP' and you basically have 'worst possible transistor', so
bad that you can't kill it.

~~~
jjoonathan
Thanks for clarifying. I chalked up the difference between 'a bit' and 'can't
kill it' to mitigations that have happened since the LM383 was designed but
now that I'm reading up on lateral transistors it looks like you're almost
certainly right.

------
wpietri
When I read things like this it amazes me that computers work at all. As
person who spends 99% of the time working on software, I so much take all of
the EE level for granted.

~~~
amelius
Well, a computer is basically a handful of gates, instantiated millions of
times. So you only have to optimize those basic gates, and because they are
(supposed to be) small, the design-space is small as well which simplifies
optimization.

The hard part is actually the parasitics that come into play
(capacitive/inductive coupling between signal lines and the bulk), and dealing
with that when synthesizing the design.

~~~
sbradford26
Digital circuits also add the joys of clocks.

------
jhallenworld
So the new LM386 is the Nsiway NS8002. This chip is better in that the output
capacitor it not required (it has two LM386s making an h-bridge). On lcsc.com,
they are $0.0329 each for QTY=10, or $0.90 for boards (each) on eBay. They are
nice if you don't want to deal with class-D switching noise.

Cheap clock radios use them. They also use an 8-pin AM/FM digital radio IC:
pins for 32 KHz crystal, I2C, antenna (loopstick for AM), and audio out. No
coils, inductors or filters needed.

~~~
voltagex_
I wonder if I can get my hands on the radio IC - I'd love to do an "overkill
breadboard" radio - connected up to a bluetooth transmitter or USB microphone
so I could have it dump into a Raspberry Pi for LAN streaming.

------
fernly
"My neighbor had just got a dog that was always barking. So I got tweeter,
built up a simple 30kHz oscillator using a LM324. Set the two LM383 to swing
rail to rail. Got a lantern battery that could put out the power. Then
connected the tweeter."

Paging Steve Gibson: somebody reinvented your dog silencer[1][2]!

[1]
[https://www.grc.com/tqc/TheQuietCanine.htm](https://www.grc.com/tqc/TheQuietCanine.htm)

[2] [https://groups.google.com/forum/#!topic/portable-sound-
blast...](https://groups.google.com/forum/#!topic/portable-sound-
blaster/4LI77KQM6xw)

~~~
justtopost
I think nearly every budding ee has built a variation of this at some point.

------
makomk
I love the part about how Chrysler somehow managed to defeat the thermal
protection and destroy the chip via a heatsink that had just the right amount
of thermal resistance to cause the transistor to heat up above its safe
operating area and cook itself whilst keeping the thermal protection circuit
cool enough not to trip.

~~~
skykooler
The paper from Chrysler is also fascinating. It's the first time I've seen
"Side of a submarine" as an element in a circuit diagram.

------
cellularmitosis
Fans of this article will also enjoy Ken Sherriff's talk at Supercon last
week:
[https://www.youtube.com/watch?v=TKi1xX7KKOI](https://www.youtube.com/watch?v=TKi1xX7KKOI)

~~~
monochromatic
Somehow I expected him to be about 30 years older.

------
gnarbarian
I love the design (or lack thereof) of this site. Courier font plus the old
scans of photocopies make it feel like i'm reading an old xeroxed white paper
(in a good way).

~~~
weinzierl
I like it as well and find it delightfully easy on the eyes.

Funny thing is that I remember that back in the day I hated those Courier-
font-style publications. They always seemed hard to read compared to well
type-set documents. And I never understood screenplay writers obsession with
Courier 12[1]. I guess the web is so noisy and cluttered today, that even
harsh black Courier on a white page is a relief.

[1] Screenplays are usually written in Courier 12. I only know that because I
sometimes read screenplays, for movies that interest me. It's fun and doesn't
take as much time as it does to watch the movie.

~~~
starbeast
>I only know that because I sometimes read screenplays, for movies that
interest me. It's fun and doesn't take as much time as it does to watch the
movie.

I don't know why I find this as hilarious as I do, but thanks for sharing.

Personally, I haven't read many screenplays, though I did read the original
one for Monty Python and the Holy Grail and it bears very little resemblance
to the final film. There's a whole section about buying pet ants from Harrods.

~~~
weinzierl
It wasn't in the Holy Grail, as far as I remember, but they actually did that
sketch:

[https://www.youtube.com/watch?v=nmKped3yARQ](https://www.youtube.com/watch?v=nmKped3yARQ)

~~~
starbeast
It was in the first draft of the Holy Grail screenplay. Mr Arthur King finds
the grail at the Harrods ant counter.

I am guessing that the Harrods sketch is from the fourth series and is
repurposing some of that material.

------
cellularmitosis
"Either 45Watts to one or 90watts to both appears to pop the plastic off the
silicon with out any apparent damage to the chip"

Oooh, found my project for the weekend!

"Now it is no longer possible to do this since the packaging department had
redesigned the package"

aww shucks

~~~
weinzierl
You can pop LED's. Maybe not quite the same but also not as expensive.

~~~
linker3000
Careful - many years ago one just missed my eye and cut my brow (unplanned
overload; no dicking around involved)

------
aidos
OT but it seems like a good place to ask:

this week I’ve been looking into making a wireless speaker similar to a Sonos
play:1. In terms of the streaming mechanism is was going to use a raspberry pi
running as a snapclient, wired to a class-d amp board and a, say, 3” driver. I
thought I would find a load of projects using a pi + amp + driver in a small
box combination, but I must be looking in the wrong place.

Does anyone have any top tips of examples of setting something like this up?
What amp / driver combination to use? I’m not looking for anything amazing,
and I’m sure round 1 will be a learning experience, but any help appreciated.

~~~
JohnBooty
If you want a box with two tweeters and a woofer for some really legit sound,
here's a design from a superstar of the DIY speaker design world:

[https://sites.google.com/site/undefinition/isetta](https://sites.google.com/site/undefinition/isetta)

He mostly just lays out the speaker and crossover design; but as he mentions a
search for "TPA3116 2.1 amp" will give you lots of results on Amazon,
AliExpress, and Parts Express.

PE's forums are good, lots of people have tackled similar projects:

[http://techtalk.parts-express.com/forum](http://techtalk.parts-
express.com/forum)

For anybody else interested in this hobby, there are lots of fantastic kits
out there, primarily for bookshelf/tower speakers and subwoofers.

[https://www.diysoundgroup.com](https://www.diysoundgroup.com)

[https://www.parts-express.com/cat/speaker-kits/286](https://www.parts-
express.com/cat/speaker-kits/286)

The product page for the C-Notes (a fantastic value at $100/pair!) kit has a
build video which gives you a great idea of the process and the tools you'll
need. Process is similar for any flat-pack kit.

[https://www.parts-express.com/c-note-mt-bookshelf-speaker-
ki...](https://www.parts-express.com/c-note-mt-bookshelf-speaker-kit-pair-
with-knock-down-cabinets--300-7140)

Of course you can also go as far down the DIY hole as you like, designing your
own electronics and selecting drivers, etc.

~~~
jimnotgym
I would love a C-note or the _Overnight Sensations_. Unfortunately UK shipping
is a bit pricey! $90...

~~~
JohnBooty
The C-Notes are still a bargain at that price!

There's about $80 worth of drivers in there, which is _bonkers_ for a $100 kit
that also includes crossover parts and MDF cabinets.

For comparison, the $130 Overnight Sensations kit contains about $55 worth of
drivers. That's a good deal, and consistent with other DIY kits... and it
illustrates what an outlier the C-Notes are.

(The reason why the C-Notes are so affordable is because Parts Express and
Dayton share corporate ownership, so presumably they're about to source those
Dayton drivers for next to nothing)

FYI there's an MTM (two woofers, one tweeter) version of the C-Notes coming in
~45 days for $100/speaker ($200/pair)

~~~
jimnotgym
I need to hunt around for a cheaper shipping forwarder I think...

------
Taniwha
ha! make sure you read the last paragraph

~~~
Koshkin
Apparently, the dog, who was prevented from barking, found some other way to
have fun...

------
ianhowson
As a kid, the LM383 had particular appeal: it was the highest-power amp chip
available that ran off a 'safe' voltage. I didn't need to do any mains wiring.

~~~
setquk
I was forever trying to find enough old car batteries to get more volts when I
was a kid for precisely this reason.

That was until I nearly burned the shed down charging one up. I was confined
to alkalines then. Boo hiss.

------
pwaivers
> _" But it is humorous when the TDA2002 is often referred to as a replacement
> for the LM383. As a matter of fact, the LM383 is really a reverse
> engineering of the TDA2002. Credit should be given to the design engineer
> Bruno Murari who was working for SGS at the time. He was the one who came up
> with a way to do an automotive power amplifier using only five pins."_

This first paragraph is almost gibberish to me. In a good way. I just find it
humorous that there are so many in-the-know words here.

~~~
anyfoo
Please don't be proud of ignorance.

TDA200 and LM383 are obviously product or device names. Bruno Murari is
obviously a person's name (a design engineer, as the sentence points out!),
SGS is obviously a place where one works, likely a company.

You should have no issues with the term "reverse engineering" if you are on
Hacker News. So that only leaves "automotive power amplifier using only five
pins". You probably know what "automotive" and "five pins" means, though, so
even less than that.

And then it's absolutely obvious that you won't know what a "power amplifier"
is if you don't have _some_ connection to electrical engineering, but it's
useless to point that out. Imagine if every electrical engineer did that on
articles on biology, chemistry or economic sciences.

~~~
Dylan16807
Or to put it another way:

These are names of things. The sentence structure makes that clear, and makes
it clear how they relate. They are not "in-the-know" terms that are lacking
definitions. It is not gibberish, just like the sentence "Jane gave Sue a
letter from Bob" is not gibberish, even though nobody defined "Jane", "Sue",
or "Bob".

