Op amps problem Gain Calculation

[Henry]

"Rich Grise" <richgrise@example.net> wrote in message
newsan.2006.01.13.01.14.48.237116@example.net...

On Wed, 11 Jan 2006 19:50:14 -0500, Henry wrote:
"Jasen Betts" <jasen@free.net.nospam.nz> wrote in message
...
probably they are. you could line them with antistatic plastc (ask at
any place that assembles computers they'll have heaps.)

Bye.
Jasen

Atually I previously asked at 3 different places (like CompUSA, etc.)
for anti-static foam or plastic and was told that they have none. Some
said they throw it away immediately, some said that it goes with the
customer.

Henry

Go to the ones that say they throw it away, and ask, "When does it
go into the dumpster? Can I wait outside for some? Thanks!"

Good Luck!
Rich

Except I live in a rural area and these places are 20-30 miles away. But I
will try again next time I make a trip to those shopping mecca areas.

Henry

 

[Henry]

"Dan Hollands" <dhollan3@rochester.rr.com> wrote in message
news:%FAxf.99404$ME5.16364@twister.nyroc.rr.com...

"Henry" <henrytj@pghmail.com> wrote in message
news:jIydne2Bg7pdM1veRVn-pA@pghconnect.com...
Probably a dumb question, but found a site about transistors. They
showed
a
PNP as being between +V and a load, and a NPN as being between the load
and
ground. Is this a conceptual convention or is this really neccessary?
Can
a
NPN be place between +V and ground. In dabbling with my old TTL chips
(7400
series) I have been using NPN for everything. (Partly cause I bought a
15
pack at RS.) But in some cases I have had to invert an output to use an
NPN. Could I use a PNP in the same situation without inverting? I have
been
using transistors for all my I/O. (mostly to a camera or a photo flash.
Like
a flash delay circuit.) I understand the basic concepts of transistors
being
amplifiers and switches (what I am doing) but dont know the practicle
dos
and donts. Although my circuits work, I am worried that I might be using
the
wrong transistors, or right ones in the wrong way.

Henry


The transistors used as drivers and invertors with TTL (+5V / Gnd) logic
are
almost always NPN transistors
The input and output voltages of TTL are most compatible with NPN

As a historical - point in the early days before ICs, PNP transistors were
much less expensive and more available than NPN and most logic system were
Gnd and -12V so that PNP transistors could be used.

--
Dan Hollands
1120 S Creek Dr
Webster NY 14580
585-872-2606
dan.hollands@gmail.com
www.QuickScoreRace.com

Okay, thanks. When I started I picked up packages of each (NPN and PNP).
Only used the NPN so far but am running low. Was wondering if I could, or
should, be using the PNP ones in cases where I was having to invert the
output for the NPNs. Guess I will have to go and buy another package of NPNs
if I want to do more.

Now, what about computer parallel port output? There is a VB DDL Win95IO
that allows a win95/98 (which is what I still use) user made program to
directly read and change the printer port pins. I was thinking of dabbling
with this to interface with a TTL/transistor circuit. Should I still use
only NPN for this?

Henry

 

[Jasen Betts]

On 2006-01-12, Henry <henrytj@pghmail.com> wrote:

Atually I previously asked at 3 different places (like CompUSA, etc.) for
anti-static foam or plastic and was told that they have none. Some said they
throw it away immediately, some said that it goes with the customer.

try smaller.

At work we mainly do support but build PC's about once a week, we're always
throwing that stuff out.

--

Bye.
Jasen

 

[Jasen Betts]

On 2006-01-12, Henry <henrytj@pghmail.com> wrote:

Probably a dumb question, but found a site about transistors. They showed a
PNP as being between +V and a load, and a NPN as being between the load and
ground. Is this a conceptual convention or is this really neccessary?

It the way that usually works best.

To turn a transistor fully on (into saturation), the base voltage has to be
slightly past collector voltage. for a NPN with collector connected to the
positive supply that'd require a drive voltage greater than the supply
voltage, which is usually inconvenient to implement.

Can a NPN be place between +V and ground.

probably not a good idea...

In dabbling with my old TTL chips (7400 series) I have been using NPN for
everything. (Partly cause I bought a 15 pack at RS.)

15 pack? so few?

But in some cases I have had to invert an output to use an
NPN. Could I use a PNP in the same situation without inverting?

maybe.

I have been using transistors for all my I/O.
(mostly to a camera or a photo flash. Like a flash delay circuit.)
I understand the basic concepts of transistors being
amplifiers and switches (what I am doing) but dont know the practicle dos
and donts. Although my circuits work, I am worried that I might be using the
wrong transistors, or right ones in the wrong way.

possibly. I mainly learned transistors by copying others.

Bye.
Jasen

 

[Jasen Betts]

On 2006-01-13, Derek Potter <dpatspothyphenonhyphensolutionsdotcodotuk@thats.all> wrote:

On Wed, 11 Jan 2006 03:41:38 -0500, "Henry" <henrytj@pghmail.com
wrote:

Okay, now that I have dabbled and put some circuits together with some 25+
year old parts (7400 series TTL). What might I do if I were to be doing this
with newer, more up to date, technology? Are there programmable controllers
on a chip that are easy to work with. Keep in mind I am looking for things
that I can do with under $50 in parts, like with the TTL gates. Is there a
relatively easy way to interface simple logic gates/transistors with a PC,
laptop, PDA, etc?

It depends whether you are trying to teach yourself the hard way or
just get on with practical design. Gate arrays are one way to go but
are relatively inflexible and I would suggest you skip them and go
straight to microcontrollers. You'll need to learn programming skills
but the Microchip PIC series are fairly easy to learn, though you will
certainly spend a lot of time learning the ropes. It's worth it
though, so Google Microchip and get hold of their data CDs, download
their MPLAB software and (horror of horrors) *buy* a PICSTART
programmer. You can get FLASH chips that avoid the need for a UV
erasor, but the cheapest chips are the ones that come in a more
expensive UVEPROM version as well as the cheaper OTP (one time
programmable) types. It's your call what you use, the different types
have different built-in peripherals, you can always start with the
simplest (but avoid the PIC16C54 as it has a cumbersome page
addressing system).

As another poster has said, the AVR-core is the other "big name" in
microcontrollers. You can get some very fancy chips in that series.

the AVR are (hardware wise) way easier to program that the PICS
you don't need 12V (only a single supply somewhere near 5V ) and
they all have 1000-rewrite flash. a reliable in-circuit programmer
can be made using a single 74hc series chip....

You may like to budget for a development board in either case.

they're nice, but breadboard etc can be used too...

Bye.
Jasen

 

[Derek Potter]

On Fri, 13 Jan 2006 13:47:07 GMT, "Dan Hollands"
<dhollan3@rochester.rr.com> wrote:

"Derek Potter" <dpatspothyphenonhyphensolutionsdotcodotuk@thats.all> wrote
in message news:3ques15r859309d1ea5b856dnrrk9bmn8s@4ax.com...
I need some information about the current approach to safety of new
equipment with regard to fire hazards created by a fault. I appreciate
there are generic standards covering the ejection of molten metal and
so on, but I am wondering about the application of the "single
component failure" concept in situations where a failure could
overload a semiconductor with the possible, though unlikely, result
that it ignites or ignites an adjacent part. I'm not asking about
*techniques* to avoid hazard, I'm asking about what is legally
required. Trick question - I'm not asking for legal advice, just
information concerning best current practice. I'm posting from the UK
but I suspect the regs will be substantially the same in all of Europe
and the US.

My particular concern is a small transistor driving an external alarm.
The power supply has a fuse but as it feeds several circuits, it
doesn't provide much protection for the external alarm circuit. I am
considering an active current limit in the supply but I still have
some reservations as to whether this meets the letter of the law. For
example, one scenario involves two events as follows:

1 The current limit fails spontaneously, but as this is not
monitored, the defect remains undetected, waiting for the second event
to happen...
2 Someone fiddles with the external wiring and causes a short.

The result is that the driver overheats, catches fire and there is
hell to pay. Now, it is perfectly true that this involves two
independent "failures" so at first sight would meet the "single
component failure" criterion. However, I suspect that a fault that is
never detected (and just lies there waiting for a chance to create a
hazard) may not count. Likewise, a fault that could be caused by Uncle
Fred with his screwdriver is hardly a spontaneous component failure.
So overall, would such a system meet the "due care" criterion?

I have severe doubts as to whether much equipment is designed with
this degree of concern but it would be goot to be ahead of the field -
without incurring too much cost.

Also, if this isn't the best newsgroup could someone point me in the
right direction? Most electronics groups seem to be full of people
selling stuff.

TIA.

Derek

If you are in the UK, you are under EU requirements and you should be
studying the appropriate IEC specs for the type of equipment you are
designing. Just as a personal opinion - if there is an output that when
shorted will cause a fire, then there should be some type of protection for
the output.

Indeed so, but my question goes a bit further as I already have
protection in the shape of a foldback regulator. It's failure of this
protection that I'm asking about. This is unlikely to cause an
immediately hazardous condition, but, obviously, if the protection
fails, the circuit is then left susceptible to any other fault. In
this case it could be a fairly rare external event. The failure of the
protection device may not be detected without yet more circuitry to
monitor the foldback operation of the regulator! Am I being too fussy?
Do most commercial and consumer devices go this far?

 

[Dan Hollands]

"Derek Potter" <dpatspothyphenonhyphensolutionsdotcodotuk@thats.all> wrote
in message news:mrrhs1heq0vhnar2g5cgibqj8fffppg0ok@4ax.com...

On Fri, 13 Jan 2006 13:47:07 GMT, "Dan Hollands"
dhollan3@rochester.rr.com> wrote:


"Derek Potter" <dpatspothyphenonhyphensolutionsdotcodotuk@thats.all> wrote
in message news:3ques15r859309d1ea5b856dnrrk9bmn8s@4ax.com...
I need some information about the current approach to safety of new
equipment with regard to fire hazards created by a fault. I appreciate
there are generic standards covering the ejection of molten metal and
so on, but I am wondering about the application of the "single
component failure" concept in situations where a failure could
overload a semiconductor with the possible, though unlikely, result
that it ignites or ignites an adjacent part. I'm not asking about
*techniques* to avoid hazard, I'm asking about what is legally
required. Trick question - I'm not asking for legal advice, just
information concerning best current practice. I'm posting from the UK
but I suspect the regs will be substantially the same in all of Europe
and the US.

My particular concern is a small transistor driving an external alarm.
The power supply has a fuse but as it feeds several circuits, it
doesn't provide much protection for the external alarm circuit. I am
considering an active current limit in the supply but I still have
some reservations as to whether this meets the letter of the law. For
example, one scenario involves two events as follows:

1 The current limit fails spontaneously, but as this is not
monitored, the defect remains undetected, waiting for the second event
to happen...
2 Someone fiddles with the external wiring and causes a short.

The result is that the driver overheats, catches fire and there is
hell to pay. Now, it is perfectly true that this involves two
independent "failures" so at first sight would meet the "single
component failure" criterion. However, I suspect that a fault that is
never detected (and just lies there waiting for a chance to create a
hazard) may not count. Likewise, a fault that could be caused by Uncle
Fred with his screwdriver is hardly a spontaneous component failure.
So overall, would such a system meet the "due care" criterion?

I have severe doubts as to whether much equipment is designed with
this degree of concern but it would be goot to be ahead of the field -
without incurring too much cost.

Also, if this isn't the best newsgroup could someone point me in the
right direction? Most electronics groups seem to be full of people
selling stuff.

TIA.

Derek

If you are in the UK, you are under EU requirements and you should be
studying the appropriate IEC specs for the type of equipment you are
designing. Just as a personal opinion - if there is an output that when
shorted will cause a fire, then there should be some type of protection
for
the output.

Indeed so, but my question goes a bit further as I already have
protection in the shape of a foldback regulator. It's failure of this
protection that I'm asking about. This is unlikely to cause an
immediately hazardous condition, but, obviously, if the protection
fails, the circuit is then left susceptible to any other fault. In
this case it could be a fairly rare external event. The failure of the
protection device may not be detected without yet more circuitry to
monitor the foldback operation of the regulator! Am I being too fussy?
Do most commercial and consumer devices go this far?

Generally equipment design for general use is only concerned with a single
failure criteria. In my experience adding more circuitry increases the
complexity to the point the failure and problems are more likely. The
problem with all redundant circuits is the need to test them to insure that
all of the redundant circuits are working. Statistical methods may be used
to determine how often the redundant circuits must be checked to achieve a
certain confidance level the system will operate properly when required. In
your case I would see no need for extra circuitry

Execeptions are things like Safety Shutdown systems, Intrinsically Safe
Equipment to insures that sparks or hot spots don't trigger an explosion in
explosive atmospheres and control systems in nuclear power plants.

 

[w_tom]

No one can accurately answer your question without numbers. Up
front, numbers such as current and voltage should have been provided.
Is this a 3 volt system or a 300,000 volt system? Also the environment
should be considered.

Which means only a generic answer can be provided. Any single point
failure has a protective backup. For example, transistor switch
current limited by an emitter resistor in series with a fuse,
polyswitch, or overvoltage crowbar. But again, we don't even know what
the danger is - with numbers. Therefore a useful answer is not
possible.

Derek Potter wrote:

I need some information about the current approach to safety of new
equipment with regard to fire hazards created by a fault. I appreciate
there are generic standards covering the ejection of molten metal and
so on, but I am wondering about the application of the "single
component failure" concept in situations where a failure could
overload a semiconductor with the possible, though unlikely, result
that it ignites or ignites an adjacent part. I'm not asking about
*techniques* to avoid hazard, I'm asking about what is legally
required. Trick question - I'm not asking for legal advice, just
information concerning best current practice. I'm posting from the UK
but I suspect the regs will be substantially the same in all of Europe
and the US.

My particular concern is a small transistor driving an external alarm.
The power supply has a fuse but as it feeds several circuits, it
doesn't provide much protection for the external alarm circuit. I am
considering an active current limit in the supply but I still have
some reservations as to whether this meets the letter of the law. For
example, one scenario involves two events as follows:

1 The current limit fails spontaneously, but as this is not
monitored, the defect remains undetected, waiting for the second event
to happen...
2 Someone fiddles with the external wiring and causes a short.

The result is that the driver overheats, catches fire and there is
hell to pay. Now, it is perfectly true that this involves two
independent "failures" so at first sight would meet the "single
component failure" criterion. However, I suspect that a fault that is
never detected (and just lies there waiting for a chance to create a
hazard) may not count. Likewise, a fault that could be caused by Uncle
Fred with his screwdriver is hardly a spontaneous component failure.
So overall, would such a system meet the "due care" criterion?
...

 

[Derek Potter]

On 14 Jan 2006 17:27:08 -0800, "w_tom" <w_tom1@usa.net> wrote:

No one can accurately answer your question without numbers. Up
front, numbers such as current and voltage should have been provided.
Is this a 3 volt system or a 300,000 volt system? Also the environment
should be considered.

Which means only a generic answer can be provided. Any single point
failure has a protective backup. For example, transistor switch
current limited by an emitter resistor in series with a fuse,
polyswitch, or overvoltage crowbar. But again, we don't even know what
the danger is - with numbers. Therefore a useful answer is not
possible.

I know what you are driving at, but how exactly will you apply the
numbers? There are plenty of regulations covering increased hazards
for, say high voltage or explosive atmosphere. I did not mention these
- obviously my question implied they do not apply. Hence I made it
explicit that I am interested in generic standards and best practice.

You should also notice that I explicitly said "small transistor" thus
ruling out 300KV and 10KA systems. I would be most interested to learn
how different voltage and current levels would affect your analysis,
given that whatever they are, they need to fit the handling capacity
of a "small transistor". How is 12V 120mA going to be any different
from, say 5V 1mA or even (pushing the "small transistor" term to its
limits) 48V, 1A?

I also suggested the Uncle Fred might fiddle with the external wiring
thus creating a hazard. Since high voltage and high current cabling is
obviously not accessible, this scenario implies that the power levels
are small - just enough to blow a "small transitor" but not enough to
warrent physically protected cables.

As for the danger, you do know what it is. I explicitly said that the
failure scenario is overload of a semiconductor - the small transistor
mentioned later - with the possible end result of ignition of the
part.

As suggested by the term "Uncle Fred", the application is domestic
consumer. However, I do not have any data on Uncle Freds so I cannot
provide numbers for you calculations.

FWIIW ,the small transistor circuit in question is a BS160 FET driving
a 12V load at 120mA but subject to possible short circuits as said.
The system fuse is 1A but fuses do not blow instantly so, with the
fairly high "on" resistance of the FET (rising as it heats up) there
is the distinct possibility of the TO92 device dissipating many watts
before failing. The electronic protection comprises a foldback
regulator and is perfectly adequate unless, of course it fails first,
leaving the circuit unprotected without any indication of the latent
problem.

Derek Potter wrote:
I need some information about the current approach to safety of new
equipment with regard to fire hazards created by a fault. I appreciate
there are generic standards covering the ejection of molten metal and
so on, but I am wondering about the application of the "single
component failure" concept in situations where a failure could
overload a semiconductor with the possible, though unlikely, result
that it ignites or ignites an adjacent part. I'm not asking about
*techniques* to avoid hazard, I'm asking about what is legally
required. Trick question - I'm not asking for legal advice, just
information concerning best current practice. I'm posting from the UK
but I suspect the regs will be substantially the same in all of Europe
and the US.

My particular concern is a small transistor driving an external alarm.
The power supply has a fuse but as it feeds several circuits, it
doesn't provide much protection for the external alarm circuit. I am
considering an active current limit in the supply but I still have
some reservations as to whether this meets the letter of the law. For
example, one scenario involves two events as follows:

1 The current limit fails spontaneously, but as this is not
monitored, the defect remains undetected, waiting for the second event
to happen...
2 Someone fiddles with the external wiring and causes a short.

The result is that the driver overheats, catches fire and there is
hell to pay. Now, it is perfectly true that this involves two
independent "failures" so at first sight would meet the "single
component failure" criterion. However, I suspect that a fault that is
never detected (and just lies there waiting for a chance to create a
hazard) may not count. Likewise, a fault that could be caused by Uncle
Fred with his screwdriver is hardly a spontaneous component failure.
So overall, would such a system meet the "due care" criterion?
...

 

[Derek Potter]

On Sat, 14 Jan 2006 15:44:06 GMT, "Dan Hollands"
<dhollan3@rochester.rr.com> wrote:

"Derek Potter" <dpatspothyphenonhyphensolutionsdotcodotuk@thats.all> wrote
in message news:mrrhs1heq0vhnar2g5cgibqj8fffppg0ok@4ax.com...
On Fri, 13 Jan 2006 13:47:07 GMT, "Dan Hollands"
dhollan3@rochester.rr.com> wrote:


"Derek Potter" <dpatspothyphenonhyphensolutionsdotcodotuk@thats.all> wrote
in message news:3ques15r859309d1ea5b856dnrrk9bmn8s@4ax.com...
I need some information about the current approach to safety of new
equipment with regard to fire hazards created by a fault. I appreciate
there are generic standards covering the ejection of molten metal and
so on, but I am wondering about the application of the "single
component failure" concept in situations where a failure could
overload a semiconductor with the possible, though unlikely, result
that it ignites or ignites an adjacent part. I'm not asking about
*techniques* to avoid hazard, I'm asking about what is legally
required. Trick question - I'm not asking for legal advice, just
information concerning best current practice. I'm posting from the UK
but I suspect the regs will be substantially the same in all of Europe
and the US.

My particular concern is a small transistor driving an external alarm.
The power supply has a fuse but as it feeds several circuits, it
doesn't provide much protection for the external alarm circuit. I am
considering an active current limit in the supply but I still have
some reservations as to whether this meets the letter of the law. For
example, one scenario involves two events as follows:

1 The current limit fails spontaneously, but as this is not
monitored, the defect remains undetected, waiting for the second event
to happen...
2 Someone fiddles with the external wiring and causes a short.

The result is that the driver overheats, catches fire and there is
hell to pay. Now, it is perfectly true that this involves two
independent "failures" so at first sight would meet the "single
component failure" criterion. However, I suspect that a fault that is
never detected (and just lies there waiting for a chance to create a
hazard) may not count. Likewise, a fault that could be caused by Uncle
Fred with his screwdriver is hardly a spontaneous component failure.
So overall, would such a system meet the "due care" criterion?

I have severe doubts as to whether much equipment is designed with
this degree of concern but it would be goot to be ahead of the field -
without incurring too much cost.

Also, if this isn't the best newsgroup could someone point me in the
right direction? Most electronics groups seem to be full of people
selling stuff.

TIA.

Derek

If you are in the UK, you are under EU requirements and you should be
studying the appropriate IEC specs for the type of equipment you are
designing. Just as a personal opinion - if there is an output that when
shorted will cause a fire, then there should be some type of protection
for
the output.

Indeed so, but my question goes a bit further as I already have
protection in the shape of a foldback regulator. It's failure of this
protection that I'm asking about. This is unlikely to cause an
immediately hazardous condition, but, obviously, if the protection
fails, the circuit is then left susceptible to any other fault. In
this case it could be a fairly rare external event. The failure of the
protection device may not be detected without yet more circuitry to
monitor the foldback operation of the regulator! Am I being too fussy?
Do most commercial and consumer devices go this far?

Generally equipment design for general use is only concerned with a single
failure criteria. In my experience adding more circuitry increases the
complexity to the point the failure and problems are more likely. The
problem with all redundant circuits is the need to test them to insure that
all of the redundant circuits are working. Statistical methods may be used
to determine how often the redundant circuits must be checked to achieve a
certain confidance level the system will operate properly when required. In
your case I would see no need for extra circuitry

Execeptions are things like Safety Shutdown systems, Intrinsically Safe
Equipment to insures that sparks or hot spots don't trigger an explosion in
explosive atmospheres and control systems in nuclear power plants.

Agreed completely and I tend to think, like you, that having a little
foldback regulator to guard against the occasional shorted load is
probably enough. The question hinges on what comprises a "single
component failure" since an external short in unprotected wiring
accessible to "Uncle Fred" is not exactly a component failure.
Likewise failure of the current limit doesn't create a fault in itself
but, as it's not going to be monitored, this doesn't quite settle the
matter - it leaves the system in a vulnerable state to an external
short.

I suppose, in a nutshell, the question comes down to whether
protection circuits are relevant to "due care" if an undetectable
failure in the protection leaves the system just as vulnerable as if
the protection were not there.

On another tack, I may work around this by fitting a fire-resistant
sleeve over the transistor. It can burn as much as it likes then, but
I was hoping to avoid the trouble.

 

[Derek Potter]

On Mon, 16 Jan 2006 13:02:01 -0500, "Henry" <henrytj@pghmail.com>
wrote:

Watch out what you get out of a camera - they often handle a couple of
hundred volts on the flash contacts if a flash gun is connected. This
is bad news for you and worse for electronic bits and pieces.

Yes, the high voltage of some flash units is one of the reasons that I want
to eventually go to opto-isolators. But my current flash units are 4v for
one, and 15v for the other. They are different types of flash units.

I learned the hard way - when the gear got wet underground. Ouch!

 

[Derek Potter]

On 16 Jan 2006 19:23:23 -0800, "w_tom" <w_tom1@usa.net> wrote:

The keyboard and mouse are connected to a 'tens of amp' power supply
with only a Polyswitch for protection. In that application, a burned
PC trace is acceptable.

Really? Who says? In the final analysis you are relying on that PCB
trace to provide fuse protection in the event of your PTC failing. Is
that really an example of the "best practice" I was asking about? I
think not!

In a machine that handled dangerous materials,
we used a small regulator AND a Polyswitch, in series, because
consequences of failure there were catastrophic. Only two layers of
protection because voltage could never exceed a regulator's maximum
input voltage.

Look, Tom. I am very grateful for the effort you have put into
answering some question or other, but it isn't the one I asked. You
may work to "industry standards" or exceed them. Or you could be a
bunch of cowboys. I don't think you are, but your ad-hoc methods
aren't relevant to my question.

As for the technique you describe, it is just an example of avoiding
the oft-cited "single component failure" criterion. Two failures are
needed to create a hazard. They are independent and, also, they are
internal. However, what I asked about was whether a rare but possible
external event would qualify.

However, even your double protection technique is suspect as the two
protection circuits are not monitored. At least, you haven'tmentioned
such a vital thing, which would be odd because monitoring both would
be relevant to my query.

Note the difference between both solutions. Details of upstream
power source and downstream consequences of failure must be considered.

Obviously.

In one appliance, a manufacturer used a circuit breaker in series
with Polyswitch. But the designer did not quite understand how
failures occur. He put two 60 volt Polyswitches in series thinking
that was equivalent to one 120 volt Polyswitch. When the circuit
breaker failed to trip, those Polyswitch devices also failed causing a
house fire. An example provided as background insight.

A pretty elementary mistake when using PTCs is to ignore thermal
runaway leading to voltage stress. Presumably his design was never run
past a professional engineer and never bench tested. Generic safety
standards do explictly prohibit counting domino failures. So just one
CB failure caused both PTCs to fail and thus only comprises a single
component failure. This is yet another example of industry *bad*
practice and whilst fairly amusing and possibly useful to amateurs is
*not* helpful as regards the interpretation of "single component
failures" in the context that I asked about, viz external cabling
faults and latent (unmonitored) internal failures.

Never used (therefore studied) those higher voltage Polyswitches; so
I am hesitant to recommend them. Numbers for incoming voltages and
currents that can damage the regulator/transistor/Polyswitch and the
downstream consequences of a failure are necessary to better answer
your question.

Actually it wasn't a question, I was correcting your implication that
PTC protection is not possible above 60V. Primary-side PTCs are
frequently buried inside mains transformers.

Again, a Polyswitch alone is sufficient for keyboard
power because consequences of a Polyswitch failure are not
catastrophic.

As I stated in my original post:

"I'm not asking about *techniques* to avoid hazard, I'm asking about
what is legally required. Trick question - I'm not asking for legal advice,
just information concerning best current practice."

"Best practice" does not mean "what would you suggest?" or "what does
your company do?" thanks all the same. My question was very specific,
about the general principle of single component failure. I am quite
capable of designing appropriate circuitry given a target performance.
It's what I do.

 

Jono wrote:

Sorry for the cross post, I think this may be the correct group to post
this. Would it be possible to connect a home thermostat to a small
portable electric heater? I am trying to control the temp in another
project inside an insulated box, and was trying to get more precise temp
control than the built in thermostat on the heater.

Yes, long as the thermstat is rated at or above the heater current. If
not, you'll need a relay as well.

NT

 

[DaemonWalker]

Try http://www.datasheet4u.com/html/M/C/1/MC1590G_Freescale.pdf.html

On 2 Aug 2003 16:27:08 -0700, krolradio@yahoo.com (Kim Roland) wrote:

I have a MC1590 (MOTOROLA)amp (can type)for a small antenna.There are
8 leads. Where would #1 pin be? The tab has a pin directly in front of
it- not on either side as in tubes or ics with a dot.I searched for a
pinout diagram & came up with a 3rd party which matches my
schematic-but dont know which is pin#1?" Any help will get me started.
Thanks.

 

[John Fields]

On 31 Jan 2006 06:40:31 -0800, "UK Pete" <kuntore@hotmail.com>
wrote:

UK Pete wrote:
Hi all,
I need to switch high voltage (1kV at 2kHz AC), low current to
sequence some electro luminescent wires. I'm working on the trigger
sequencer and I have the high voltage/ high frequency PSU but I'm not
sure what kind of device/technique to use for the actual switching
between 5 channels. Any suggestions greatfully received.
Thanks in advance,
UK Pete

.. Ooops Make that 200V AC @ 2kHz...

---
http://www.clare.com/home/pdfs.nsf/www/LCA110L_R1_0.qxd.pdf/$file/LCA110L_R1_0.qxd.pdf

Or, check this page for a lot of choices:

http://www.clare.com/Products/SSR.htm

Also: IR, Aromat(NAIS), or google "solid state rerlay"


--
John Fields
Professional Circuit Designer

 

[UK Pete]

Sorry Dan, I should have made that clear. The AC is 2 kHz but the
switching speed is only up to 20Hz and it looks like John has found the
ideal component. The only problem is I can't find a supplier that
doesn't sell them by the dozen or so. I can't even find a price on
them. I want to ideally keep the cost low as possible.
Thanks for the replies!

UK Pete

 

[Jasen Betts]

On 2006-02-01, John Fields <jfields@austininstruments.com> wrote:

Hi all,
I need to switch high voltage (1kV at 2kHz AC), low current to
sequence some electro luminescent wires. I'm working on the trigger
sequencer and I have the high voltage/ high frequency PSU but I'm not
sure what kind of device/technique to use for the actual switching
between 5 channels. Any suggestions greatfully received.
Thanks in advance,
UK Pete

.. Ooops Make that 200V AC @ 2kHz...

MOC3021 (upto 100mA) If you're in the UK that part (or similar) should be readily
available, it's an optocoupler used to drive triacs but also seems suitable to
switching 200VAC at low currents.

I don't think so.

His 200V drive is almost for sure going to be coming from an
inverter with a rectangular output waveform.

and that'll be a problem ?
could it be solved using some sort of low-pass filter?

Take a look at pages 4 and 5 of:

I'm not sure what to look for
I see a curve for on voltage that puts it at around 1.5 for 100mA
150mW is well within the reasonable range.

I see figure 5, and the circuit top of page 5

200vX200Khz 80000V/s = 0.08V/us if a triangle wave
more if a sine wave, yet more if a square wave.
but with a square wave would switching on a little late be a problem?

Is a solid state relay likely to perform better?

http://www.fairchildsemi.com/ds/MO%2FMOC3021-M.pdf

thanks for searching that out, I'd misplaced my copy and was looking at a
summary in a paper catalogue.


I see the bit that says "This optocoupler should not be used to drive a load
directly, it is intended to be a trigger device only."

But these electroluminescent wires only draw a few milliamps it's not like
trying to switch a lightbulb where the cold current can be a few amps.

What am I missing?


--

Bye.
Jasen

 

[John Fields]

On Thu, 02 Feb 2006 10:15:23 -0000, Jasen Betts <jasen@free.net.nz>
wrote:

On 2006-02-01, John Fields <jfields@austininstruments.com> wrote:

Hi all,
I need to switch high voltage (1kV at 2kHz AC), low current to
sequence some electro luminescent wires. I'm working on the trigger
sequencer and I have the high voltage/ high frequency PSU but I'm not
sure what kind of device/technique to use for the actual switching
between 5 channels. Any suggestions greatfully received.
Thanks in advance,
UK Pete

.. Ooops Make that 200V AC @ 2kHz...

MOC3021 (upto 100mA) If you're in the UK that part (or similar) should be readily
available, it's an optocoupler used to drive triacs but also seems suitable to
switching 200VAC at low currents.

I don't think so.

His 200V drive is almost for sure going to be coming from an
inverter with a rectangular output waveform.

and that'll be a problem ?
could it be solved using some sort of low-pass filter?

---
Not likely, since the color and, to a lesser extent, the intensity
of the light coming from the EL wires will change if the waveshape
of the signal driving them changes.

But, the point is, why bother?

Using a proper SSR will preserve the shape of the driving signal and
eliminate the possibility of any commutation problems which might
come up using a thyristor switch.
---

Take a look at pages 4 and 5 of:

I'm not sure what to look for
I see a curve for on voltage that puts it at around 1.5 for 100mA
150mW is well within the reasonable range.

I see figure 5, and the circuit top of page 5

200vX200Khz 80000V/s = 0.08V/us if a triangle wave
more if a sine wave, yet more if a square wave.

---
You're reading it wrong. Notice that at 20C the maximum rate of
change is 10V/ľs. That means that if you try to switch a signal
which goes from zero volts to ten volts in one microsecond you'll be
OK, but if you try to switch a signal which goes from zero volts to
eleven volts in a microsecond, you won't.

That means that for the OP's signal, which is making 200 volt
transitions, those transitions need to take longer than 20ľs for
commutation not to occur.
---

but with a square wave would switching on a little late be a problem?

---
No, commutation would.
---

Is a solid state relay likely to perform better?

---
Yes.

With a solid state relay there will be no commutation problems.
---

http://www.fairchildsemi.com/ds/MO%2FMOC3021-M.pdf

thanks for searching that out, I'd misplaced my copy and was looking at a
summary in a paper catalogue.


I see the bit that says "This optocoupler should not be used to drive a load
directly, it is intended to be a trigger device only."

But these electroluminescent wires only draw a few milliamps it's not like
trying to switch a lightbulb where the cold current can be a few amps.

What am I missing?

---
Even with a resistive load, the rate of change of the signal out of
the inverter, when it switches, is likely to turn on the bilateral
switch whether the LED is on or not. With a capacitive load (EL
wires look like lossy capacitors) the problem will be aggravated
aggravated.

Try this link:

http://www.onsemi.com/pub/Collateral/HBD855-D.PDF


--
John Fields
Professional Circuit Designer

 

[John Fields]

On 3 Feb 2006 06:27:02 -0800, "UK Pete" <kuntore@hotmail.com> wrote:

Wow. Thanks for all the thought and time taken to post replies!
I looked at the waveform from the inverter on a 'scope and found it to
be nearer 130V and around 5kHz which wasn not as it was specified to
me. The waveform appeared not too far off sinusoidal which I was
surprised at. I also found some MOC 3020s on Ebay and paid just 18
pence each for them so I'll give them a go anyway.
Let me know if you want a couple of them to play with and I'll stick
'em in the post for free.
Thanks again,

---
You're welcome, and thanks for the offer, I'll take it!

I'll email you my physical address.


--
John Fields
Professional Circuit Designer

 

[Ameen]

"there are cards you can buy that will plug in to the computer and
bring in these values."

this will make my job easier !!

please give me information about these cards.
Thier names, types, what is the best for my project and where to find
them.

thank u for your replay.