Triggering 555 Monostable

[Tim Dicus]

"John Woodgate" <jmw@jmwa.demon.contraspam.yuk> wrote in message news:J6r3IxDozoEAFw5p@jmwa.demon.co.uk...

I read in sci.electronics.design that Tim Dicus <tim@prolectron.com
wrote (in <5JvQb.9264$ZJ1.6613@lakeread01&gt about 'Triggering 555
Monostable', on Sat, 24 Jan 2004:

Yes, sir! That is EXACTLY what I need! If you would be so kind as to
point me in the direction of where I can be assured that the LM555
trigger input pin 2 has that feature.

I don't know that it does, I just suggest that you MIGHT be lucky in
that a parasitic device that isn't on the functional schematic might do
exactly what you want.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

Thanks, John.

I must admit I am not very lucky. I am one of those people who must rely on his skill.

Maybe I will be lucky enough to have a manufacturer rep (like Paul Groehe from Nat Semi) pick up on this thread.

I am hoping that the 555 has this feature. One more part I can eliminate!

Tim

 

[Jim Thompson]

On Sat, 24 Jan 2004 10:29:28 +0000, Terry Pinnell
<terrypinDELETE@dial.pipexTHIS.com> wrote:

"Tim Dicus" <tim@prolectron.com> wrote:

"Terry Pinnell" <terrypinDELETE@dial.pipexTHIS.com> wrote in message
news:va4v009h0nc2jus4bd6ce2lnd05prs03a3@4ax.com...
John Popelish <jpopelish@rica.net> wrote:
... and diode to Vcc to prevent excessive positive
excursions at end of trigger signal pulse

John, Tim:

According to Jim Thompson on 5th Jan, that limiting diode (which I'd
been using for as long as I can remember) is redundant. I've therefore
ommitted it subsequently from a couple of projects. Do you agree this
is safe?

From: Jim Thompson <invalid@invalid.invalid
Newsgroups: alt.binaries.schematics.electronic
Subject: Re: Need to mod door bell
Message-ID: <qr2jvvguofv1oblpekcp66e3u5ep06nek4@4ax.com

--
Terry Pinnell
Hobbyist, West Sussex, UK


Hi Terry,

The trigger input pin 2 on the LM555 is connected directly to the base of a
PNP transistor with no other connections or devices. See the schematic
diagram here:
http://www.national.com/ds/LM/LM555.pdf

There was a discussion last year (July 2003) on the sci.electronics.design
group about reverse voltage on the base-emitter junction of bipolar
transistors, in particular a 2N3906(PNP).

I agree with the following people. I use the diode, and will continue to do
so.

These are excerpts from that discussion:
------
Jim Thompson said:

It will fail. Devices subjected to this sort of repetitive reverse bias of
the B-E junction gradually lose Beta.

It can take awhile, although high temperatures will accelerate the effect.
For example, under the hood of a car, failure occurs within 1-2 days.
------
Jim Thompson later responded to this question:

Hey, Jim,

Is this true for small reverse b-e currents?


John


I don't know if there's a lower limit where damage doesn't occur. My
experience was in an automotive application at ~1mA.

I just make it a rule *not* to breakdown B-E junctions.

...Jim Thompson
------
Watson A Name said:

I told a guy that he was full of bs when he told us this in the ngs. He said
that putting reverse current thru the E-B junction of a transistor will
degrade the transistor's gain. I didn't believe him, so I tried it with a
few mA, and found that the transistor went from a gain of about 100 before
to a gain of less than 30 after just a half hour of reverse current of a few
mA. I was dumbfounded. It was
really true. Take a transistor and try it if you don't believe me.

If you're going to subject the transistor's E-B to reverse voltage greater
than its max rating, put a diode in series with the base or use a voltage
divider. But by all means, protect it, or else you _will_ find that the
transistor becomes degraded.
------

I rest my case.

Tim

Thanks Tim, but did you read the more recent thread I referenced? In
that, I concluded Jim was saying the diode was redundant. Perhaps he
could comment? (I'd email him to be sure he sees this, but don't
appear to have a valid email address.)

Bipolar 555's:

Input is a lateral PNP with breakdown in both directions approaching
typically 30V. So no protection is needed.

CMOS 555's:

Input is a CMOS gate. The pin is protected with ESD diodes. The only
proviso with ESD diodes is to stay well below the latch-up current
rating. Thus you should use a series resistor to set that max
current.

You can also go first class and use John Field's network and never
forward bias the ESD diode.

General:

Any protection scheme will load your input RC. Be sure to figure that
into your calculations.

My rule against reverse biasing the B-E junction of *regular*
transistors still holds. As another poster has pointed out, beta
degradation happens rapidly. I initially discovered the problem when
using B-E junctions for zeners in alternator regulator chips in the
early '60's... add Arizona heat and they die in less than a day.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[Jim Thompson]

On Sat, 24 Jan 2004 15:19:04 +0000, John Woodgate
<jmw@jmwa.demon.contraspam.yuk> wrote:

I read in sci.electronics.design that Tim Dicus <tim@prolectron.com
wrote (in <5JvQb.9264$ZJ1.6613@lakeread01&gt about 'Triggering 555
Monostable', on Sat, 24 Jan 2004:

Yes, sir! That is EXACTLY what I need! If you would be so kind as to
point me in the direction of where I can be assured that the LM555
trigger input pin 2 has that feature.

I don't know that it does, I just suggest that you MIGHT be lucky in
that a parasitic device that isn't on the functional schematic might do
exactly what you want.

Lateral PNP..........


B E C
_____________|________|________|________________________________
| | |_____| |_____| <- P-type diffusions | |
| | | |
| | N-type epitaxial material (NPN collector) | |
__| |____________________________________________________| |__
^ ^
P-iso P-type substrate P-iso

________________________________________________________________


Base can't go below one-diode drop below substrate (ground in the case
of LM339 and LM324... look at the data sheet warnings).

Base can go arbitrarily high (until breakdown).

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[Spehro Pefhany]

On Sat, 24 Jan 2004 09:10:33 -0700, the renowned Jim Thompson
<thegreatone@example.com> wrote:

On Sat, 24 Jan 2004 15:19:04 +0000, John Woodgate
jmw@jmwa.demon.contraspam.yuk> wrote:

I read in sci.electronics.design that Tim Dicus <tim@prolectron.com
wrote (in <5JvQb.9264$ZJ1.6613@lakeread01&gt about 'Triggering 555
Monostable', on Sat, 24 Jan 2004:

Yes, sir! That is EXACTLY what I need! If you would be so kind as to
point me in the direction of where I can be assured that the LM555
trigger input pin 2 has that feature.

I don't know that it does, I just suggest that you MIGHT be lucky in
that a parasitic device that isn't on the functional schematic might do
exactly what you want.

Lateral PNP..........


B E C
_____________|________|________|________________________________
| | |_____| |_____| <- P-type diffusions | |
| | | |
| | N-type epitaxial material (NPN collector) | |
__| |____________________________________________________| |__
^ ^
P-iso P-type substrate P-iso

________________________________________________________________


Base can't go below one-diode drop below substrate (ground in the case
of LM339 and LM324... look at the data sheet warnings).

Base can go arbitrarily high (until breakdown).

...Jim Thompson

I thought you didn't do ASCII art, Jim. ;-) Very nice.

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

 

[John Woodgate]

I read in sci.electronics.design that Jim Thompson
<thegreatone@example.com> wrote (in <jv4510lgnaumd4679kadiudd6tl1vs5u5u@
4ax.com&gt about 'Triggering 555 Monostable', on Sat, 24 Jan 2004:

My rule against reverse biasing the B-E junction of *regular*
transistors still holds. As another poster has pointed out, beta
degradation happens rapidly. I initially discovered the problem when
using B-E junctions for zeners in alternator regulator chips in the
early '60's... add Arizona heat and they die in less than a day.

What happens to reverse-biased b-e junctions used as noise sources?
Presumably beta degradation doesn't matter, but are there any other
adverse effects?
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[Jim Thompson]

On Sat, 24 Jan 2004 15:05:11 GMT, Fred Bloggs <nospam@nospam.com>
wrote:

Tim Dicus wrote:
"Fred Bloggs" <nospam@nospam.com> wrote in message news:40126D8E.1070001@nospam.com...


[snip]
Hi Fred,

Your argument is very logical. However, I would logically deduce from the Vcc max rating that the transistors are rated at 18 volts,
rather than "probably 30".

I agree the trigger input will take more than Vcc. I know that from experience. But how much more (and for how long) is the question
I have. From experience, I know it will take at least .75 volt above Vcc, at least intermittently.

A 2N3906 shows a base-emitter junction voltage limit at -6 volts (PNP), but shows no "base-emitter reverse voltage" limit. Can one
assume it has no reverse voltage limit? Or would one assume the limit would be +6 volts? Or +40 volts?See the following datsheet:
http://www.semiconductors.philips.com/acrobat/datasheets/2N3906_3.pdf

Once again, my concern here is I want my designs to be reliable without wasting money on parts I don't need.

Thanks,

Tim



The National single supply comparators and opamps using the same process
are spec'ed to 30V and that is where I pulled that number from. For some
reason they give no spec in their Abs Max rating chart for the 555- so
you're right in saying it can't be assumed.

Fred,

You're are right on with the 30V... it's the BVCBO rating of the
process. The 18V operating limit comes from BVCEO considerations.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[Jim Thompson]

On Sat, 24 Jan 2004 16:11:59 GMT, Spehro Pefhany
<speffSNIP@interlogDOTyou.knowwhat> wrote:

On Sat, 24 Jan 2004 09:10:33 -0700, the renowned Jim Thompson
thegreatone@example.com> wrote:

On Sat, 24 Jan 2004 15:19:04 +0000, John Woodgate
jmw@jmwa.demon.contraspam.yuk> wrote:

I read in sci.electronics.design that Tim Dicus <tim@prolectron.com
wrote (in <5JvQb.9264$ZJ1.6613@lakeread01&gt about 'Triggering 555
Monostable', on Sat, 24 Jan 2004:

Yes, sir! That is EXACTLY what I need! If you would be so kind as to
point me in the direction of where I can be assured that the LM555
trigger input pin 2 has that feature.

I don't know that it does, I just suggest that you MIGHT be lucky in
that a parasitic device that isn't on the functional schematic might do
exactly what you want.

Lateral PNP..........


B E C
_____________|________|________|________________________________
| | |_____| |_____| <- P-type diffusions | |
| | | |
| | N-type epitaxial material (NPN collector) | |
__| |____________________________________________________| |__
^ ^
P-iso P-type substrate P-iso

________________________________________________________________


Base can't go below one-diode drop below substrate (ground in the case
of LM339 and LM324... look at the data sheet warnings).

Base can go arbitrarily high (until breakdown).

...Jim Thompson

I thought you didn't do ASCII art, Jim. ;-) Very nice.

Best regards,
Spehro Pefhany

I'm in a good mood this morning. It's raining gently, very pleasant
to sit on the patio sipping coffee and watching it come down.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[Jim Thompson]

On Sat, 24 Jan 2004 16:12:59 +0000, John Woodgate
<jmw@jmwa.demon.contraspam.yuk> wrote:

I read in sci.electronics.design that Jim Thompson
thegreatone@example.com> wrote (in <jv4510lgnaumd4679kadiudd6tl1vs5u5u@
4ax.com&gt about 'Triggering 555 Monostable', on Sat, 24 Jan 2004:

My rule against reverse biasing the B-E junction of *regular*
transistors still holds. As another poster has pointed out, beta
degradation happens rapidly. I initially discovered the problem when
using B-E junctions for zeners in alternator regulator chips in the
early '60's... add Arizona heat and they die in less than a day.

What happens to reverse-biased b-e junctions used as noise sources?
Presumably beta degradation doesn't matter, but are there any other
adverse effects?

If you care about beta, have at it.

Beware that if you reverse bias into breakdown, the breakdown
gradually fades away. Add significant heat and it's a rapid
degradation.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[Winfield Hill]

Spehro Pefhany wrote...

the renowned Jim Thompson wrote:

Lateral PNP..........


B E C
_____________|________|________|________________________________
| | |_____| |_____| <- P-type diffusions | |
| | | |
| | N-type epitaxial material (NPN collector) | |
__| |____________________________________________________| |__
^ ^
P-iso P-type substrate P-iso

________________________________________________________________


Base can't go below one-diode drop below substrate (ground in the
case of LM339 and LM324... look at the data sheet warnings).

Base can go arbitrarily high (until breakdown).

...Jim Thompson

I thought you didn't do ASCII art, Jim. ;-) Very nice.

Indeed, very nice, Jim! Plus it'll stay forever in the Google
usenet archives, so we can definitely use more of the same!

Thanks,
- Win

whill_at_picovolt-dot-com

 

[John Woodgate]

I read in sci.electronics.design that Jim Thompson
<thegreatone@example.com> wrote (in <s885109v9qb9vg4gbvdirh5de64cg0spak@
4ax.com&gt about 'Triggering 555 Monostable', on Sat, 24 Jan 2004:

Beware that if you reverse bias into breakdown, the breakdown gradually
fades away. Add significant heat and it's a rapid degradation.

So it's better to use a 'zener' (above 6.8 V) as a noise source?

AIUI, one isn't closely Gaussian, but the noise voltage difference
between two similar 'zeners' is very closely Gaussian.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[Jim Thompson]

On Sat, 24 Jan 2004 17:18:40 +0000, John Woodgate
<jmw@jmwa.demon.contraspam.yuk> wrote:

I read in sci.electronics.design that Jim Thompson
thegreatone@example.com> wrote (in <s885109v9qb9vg4gbvdirh5de64cg0spak@
4ax.com&gt about 'Triggering 555 Monostable', on Sat, 24 Jan 2004:

Beware that if you reverse bias into breakdown, the breakdown gradually
fades away. Add significant heat and it's a rapid degradation.

So it's better to use a 'zener' (above 6.8 V) as a noise source?

AIUI, one isn't closely Gaussian, but the noise voltage difference
between two similar 'zeners' is very closely Gaussian.

I'm not conversant in noise sources. I just use a commercial meter
when I need a reading. Probably last *measured* noise figure 25 years
ago ;-)

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[Jim Thompson]

On 24 Jan 2004 09:07:46 -0800, Winfield Hill
<Winfield_member@newsguy.com> wrote:

Spehro Pefhany wrote...

the renowned Jim Thompson wrote:

Lateral PNP..........


B E C
_____________|________|________|________________________________
| | |_____| |_____| <- P-type diffusions | |
| | | |
| | N-type epitaxial material (NPN collector) | |
__| |____________________________________________________| |__
^ ^
P-iso P-type substrate P-iso

________________________________________________________________


Base can't go below one-diode drop below substrate (ground in the
case of LM339 and LM324... look at the data sheet warnings).

Base can go arbitrarily high (until breakdown).

...Jim Thompson

I thought you didn't do ASCII art, Jim. ;-) Very nice.

Indeed, very nice, Jim! Plus it'll stay forever in the Google
usenet archives, so we can definitely use more of the same!

Thanks,
- Win

whill_at_picovolt-dot-com

Rectilinear is easy, schematics not so. Plus most of my stuff won't
fit within the "wrap".

Maybe someone will come up with a Schematics-to-ASCII converter ?

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[Georg Acher]

In article <kfc5101btjihvt9jeevf55f83pd3fb7g75@4ax.com>,
Jim Thompson <thegreatone@example.com> writes:

|> Maybe someone will come up with a Schematics-to-ASCII converter ?

Not exactly a converter, but better than nothing:

http://www.tech-chat.de/AAcircuit.html

--
Georg Acher, acher@in.tum.de
http://wwwbode.in.tum.de/~acher
"Oh no, not again !" The bowl of petunias

 

[John Woodgate]

I read in sci.electronics.design that Jim Thompson
<thegreatone@example.com> wrote (in <kfc5101btjihvt9jeevf55f83pd3fb7g75@
4ax.com&gt about 'IC structures, lateral PNP', on Sat, 24 Jan 2004:

Plus most of my stuff won't fit
within the "wrap".

Cut down on the solid filling and add more wine, then.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[Jim Thompson]

On 24 Jan 2004 18:23:07 GMT, acher@in.tum.de (Georg Acher) wrote:

In article <kfc5101btjihvt9jeevf55f83pd3fb7g75@4ax.com>,
Jim Thompson <thegreatone@example.com> writes:

|> Maybe someone will come up with a Schematics-to-ASCII converter ?

Not exactly a converter, but better than nothing:

http://www.tech-chat.de/AAcircuit.html

I have a copy. Clever!

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[Jim Thompson]

On Sat, 24 Jan 2004 18:24:53 +0000, John Woodgate
<jmw@jmwa.demon.contraspam.yuk> wrote:

I read in sci.electronics.design that Jim Thompson
thegreatone@example.com> wrote (in <kfc5101btjihvt9jeevf55f83pd3fb7g75@
4ax.com&gt about 'IC structures, lateral PNP', on Sat, 24 Jan 2004:

Plus most of my stuff won't fit
within the "wrap".

Cut down on the solid filling and add more wine, then.

That'll work ;-)

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[Tim Dicus]

"Jim Thompson" <thegreatone@example.com> wrote in message newsj551094ud9igp6vb8q278nl94ku7d87vc@4ax.com...

On Sat, 24 Jan 2004 15:19:04 +0000, John Woodgate
jmw@jmwa.demon.contraspam.yuk> wrote:

I read in sci.electronics.design that Tim Dicus <tim@prolectron.com
wrote (in <5JvQb.9264$ZJ1.6613@lakeread01&gt about 'Triggering 555
Monostable', on Sat, 24 Jan 2004:

Yes, sir! That is EXACTLY what I need! If you would be so kind as to
point me in the direction of where I can be assured that the LM555
trigger input pin 2 has that feature.

I don't know that it does, I just suggest that you MIGHT be lucky in
that a parasitic device that isn't on the functional schematic might do
exactly what you want.

Lateral PNP..........


B E C
_____________|________|________|________________________________
| | |_____| |_____| <- P-type diffusions | |
| | | |
| | N-type epitaxial material (NPN collector) | |
__| |____________________________________________________| |__
^ ^
P-iso P-type substrate P-iso

________________________________________________________________


Base can't go below one-diode drop below substrate (ground in the case
of LM339 and LM324... look at the data sheet warnings).

Base can go arbitrarily high (until breakdown).

...Jim Thompson

Hi Jim,

How would someone figure that out from the datasheet or an application note? There isn't mention that I can find that separates that
transistor from a standard PNP type.

Since most reputable sources here agree with you (right?), I will accept that you speak the truth.

I'm just curious how to tell the difference. Did I miss something on the literature? Is it the way the circuit is set up (the
Darlington-looking setup)? Or did you find out from some other source?

Thanks,

Tim

 

[Jim Thompson]

On Sat, 24 Jan 2004 13:29:26 -0600, "Tim Dicus" <tim@prolectron.com>
wrote:

"Jim Thompson" <thegreatone@example.com> wrote in message newsj551094ud9igp6vb8q278nl94ku7d87vc@4ax.com...
On Sat, 24 Jan 2004 15:19:04 +0000, John Woodgate
jmw@jmwa.demon.contraspam.yuk> wrote:

I read in sci.electronics.design that Tim Dicus <tim@prolectron.com
wrote (in <5JvQb.9264$ZJ1.6613@lakeread01&gt about 'Triggering 555
Monostable', on Sat, 24 Jan 2004:

Yes, sir! That is EXACTLY what I need! If you would be so kind as to
point me in the direction of where I can be assured that the LM555
trigger input pin 2 has that feature.

I don't know that it does, I just suggest that you MIGHT be lucky in
that a parasitic device that isn't on the functional schematic might do
exactly what you want.

Lateral PNP..........


B E C
_____________|________|________|________________________________
| | |_____| |_____| <- P-type diffusions | |
| | | |
| | N-type epitaxial material (NPN collector) | |
__| |____________________________________________________| |__
^ ^
P-iso P-type substrate P-iso

________________________________________________________________


Base can't go below one-diode drop below substrate (ground in the case
of LM339 and LM324... look at the data sheet warnings).

Base can go arbitrarily high (until breakdown).

...Jim Thompson

Hi Jim,

How would someone figure that out from the datasheet or an application note? There isn't mention that I can find that separates that
transistor from a standard PNP type.

Since most reputable sources here agree with you (right?), I will accept that you speak the truth.

I'm just curious how to tell the difference. Did I miss something on the literature? Is it the way the circuit is set up (the
Darlington-looking setup)? Or did you find out from some other source?

Thanks,

Tim

Except for some of the exotic processes that I work with (say PolarFab
ABC3/RFBC1) there ain't no such thing as a *real* PNP.

The schematic on the data sheet is pretty close to real-life.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[Tim Dicus]

tim@prolectron.com

"Jim Thompson" <thegreatone@example.com> wrote in message news:iip510lvf2plb1991ilmbil21isjkqbmt8@4ax.com...

On Sat, 24 Jan 2004 13:29:26 -0600, "Tim Dicus" <tim@prolectron.com
wrote:

"Jim Thompson" <thegreatone@example.com> wrote in message newsj551094ud9igp6vb8q278nl94ku7d87vc@4ax.com...
On Sat, 24 Jan 2004 15:19:04 +0000, John Woodgate
jmw@jmwa.demon.contraspam.yuk> wrote:

I read in sci.electronics.design that Tim Dicus <tim@prolectron.com
wrote (in <5JvQb.9264$ZJ1.6613@lakeread01&gt about 'Triggering 555
Monostable', on Sat, 24 Jan 2004:

Yes, sir! That is EXACTLY what I need! If you would be so kind as to
point me in the direction of where I can be assured that the LM555
trigger input pin 2 has that feature.

I don't know that it does, I just suggest that you MIGHT be lucky in
that a parasitic device that isn't on the functional schematic might do
exactly what you want.

Lateral PNP..........


B E C
_____________|________|________|________________________________
| | |_____| |_____| <- P-type diffusions | |
| | | |
| | N-type epitaxial material (NPN collector) | |
__| |____________________________________________________| |__
^ ^
P-iso P-type substrate P-iso

________________________________________________________________


Base can't go below one-diode drop below substrate (ground in the case
of LM339 and LM324... look at the data sheet warnings).

Base can go arbitrarily high (until breakdown).

...Jim Thompson

Hi Jim,

How would someone figure that out from the datasheet or an application note? There isn't mention that I can find that separates
that
transistor from a standard PNP type.

Since most reputable sources here agree with you (right?), I will accept that you speak the truth.

I'm just curious how to tell the difference. Did I miss something on the literature? Is it the way the circuit is set up (the
Darlington-looking setup)? Or did you find out from some other source?

Thanks,

Tim



Except for some of the exotic processes that I work with (say PolarFab
ABC3/RFBC1) there ain't no such thing as a *real* PNP.

Aw, come on! I've had one in my hand at some time or another. Felt pretty "real" to me !^) Just kidding.

So what I hear from you is, unless I am kinda familiar with the process to construct this beast, it would be difficult to tell?
Considering that, it seems even more important that this info is put on the datasheet somewhere!

Thanks for your time and valuable input!

Tim

 

[budgie]

On Sat, 24 Jan 2004 06:33:04 -0600, "Tim Dicus" <tim@prolectron.com> wrote:

(snip review)

So what Jim is saying is that I can connect the trigger input pin 2 to my automobile ignition coil (about 400v flyback last time I
measured) and it will do ok?

It is possible that the junction will take a small amount of reverse voltage without harm, but since nobody seems to know where that
limit is, I will use the protection diode. Even though I know it is almost impossible to do, I try to design my circuits to be
"bulletproof".

I have been at this for a while, and I have yet to see a semiconductor junction that does not have limits in both directions.

But there is one thing I know for certain:
I know nothing for certain!

I would use both a clamp diode, AND a series resistor to avoid diode failure.