Chip with simple program for Toy

[Robert Monsen]

Fuses are meant to protect your load, but that isn't what you are interested
in, right?

What you really want is some kind of current limit, so you don't whack your
computer when you short the load.

One easy way would be to use a jfet as a current limiting device:

5v
|
your load
|
n channel jfet drain connects here
|
n channel jfet source connects here
|
Resistor
|
n channel jfet gate connects here
|
Ground Return

Try a JFET like a BF245, with R = 100.

The total voltage drop for a 1k load is about .7 volts. With a short across
the load, you only draw 10ma.

Varying the R will vary the amount of current your load can draw. The real
current limit has to do with Vgs curves of the jfet you are using. The idea
is that if the IR drop across R gets large, the Vgs of the jfet will also
increase, causing the jfet to shut down.

Whether this will work depends on your application, of course.

Regards

"Philippe Signoret" <philippe_signoret@hotmail.com> wrote in message
news:8d1b98ae.0307262224.7207b640@posting.google.com...

Is there a simple circuit (or IC) that can be built to counter act a
short circuit?
I am talking about something that will cut off power if there is a
short circuit.

For example, I can get +5vdc from a disc drive power cable inside the
computer, but if I short it I have to restart the computer, and I am
sure it is not good for the computer.

Is there a way to cut off power for my circuit connected to the
computer?

I hope you understood me somewhat, I found this very difficult to
explain without an image.

Thanks in advance,
Philippe Signoret

 

[cpemma]

"pic" <<> wrote in message news:bfc4uq01l2c@enews4.newsguy.com...

Hello all,
Where can I buy pic microcontrollers. The selection in maplin
is limited, are there any other sources?

Check out Rapid Electronics http://www.rapidelectronics.co.uk/ and ESR

http://www.users.zetnet.co.uk/esr/catalogue.html

Both are far cheaper than Maplin. ESR have less range but low delivery
charges.

 

[Ziguy]

I was trying to do some analysis and for simplicity I used a sphere instead
of a box to calculate the thermal resistance and I came to a strange
conclusion.

The thermal resistance of a sphere is 1/(4*pi*k*r), where k is the thermal
conductivity and r is the radius of the sphere. A you can see, the thermal
resistance is inversely proportional to the radius. So it mean that if you
increase the sphere, the delta temperature between the center and the
surface of it will decrease . I would have sais the opposite, no?


"Roy McCammon" <rbmccammon@ieee.org> a écrit dans le message de
news:3F233AEC.3070703@ieee.org...

Ziguy wrote:
I need to calculate the Inside to ambiant thermal resistance of a small
plastic box filled with potted resin... How do I calculate that, what're
the
properties needed?

As a first approximation, you can take the resin
filled box as all the same temperature and the
thermal resistance from the case to the air
will determine the box/resin temperature.

Achilles: I wish my wish would not be granted.
an undescribable event occurs
Achilles: What happened? Where's my Genie?
Tortoise: Our context got restored incorrectly.
Achilles: What does that cryptic comment mean?
Tortoise: The system crashed.


To email me send to :

rb <my last name> AT ieee DOT org

 

[Jim Thompson]

On Sun, 27 Jul 2003 17:44:59 -0400, "Ziguy"
<robertlatour54@hotmail.NOSPAM.com> wrote:

I was trying to do some analysis and for simplicity I used a sphere instead
of a box to calculate the thermal resistance and I came to a strange
conclusion.

The thermal resistance of a sphere is 1/(4*pi*k*r), where k is the thermal
conductivity and r is the radius of the sphere. A you can see, the thermal
resistance is inversely proportional to the radius. So it mean that if you
increase the sphere, the delta temperature between the center and the
surface of it will decrease . I would have sais the opposite, no?

You have more surface area so the power is spread out. But your
thermal resistance is higher.

Also, you should be using a non-point-source for the power
representation.

...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 | |
| Jim-T@analog_innovations.com Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

For proper E-mail replies SWAP "-" and "_"

Get Lolita Out of Debt... Add Three Inches to Your Mortgage!

 

[Ziguy]

If I sink a TO220 in the middle of a 10cm sphere made of general poting
epoxy (k = 0.682 W/m*K), it wil have a case to sphere's surface thermal
resistance of only 1.2 °C/W (I considered the TO200 has a pontual heat
source). Since the area of that sphere is 1000 time bigger than the TO220
case's surface, is it correct to say that the case to ambiant thermal
resistance of that configuration will have a lot lot less thermal resistance
than a TO220 in free air, no?

Thanks


"Ziguy" <robertlatour54@hotmail.NOSPAM.com> a écrit dans le message de
news:sJXUa.746$mv6.143210@news20.bellglobal.com...

I was trying to do some analysis and for simplicity I used a sphere
instead
of a box to calculate the thermal resistance and I came to a strange
conclusion.

The thermal resistance of a sphere is 1/(4*pi*k*r), where k is the thermal
conductivity and r is the radius of the sphere. A you can see, the thermal
resistance is inversely proportional to the radius. So it mean that if you
increase the sphere, the delta temperature between the center and the
surface of it will decrease . I would have sais the opposite, no?


"Roy McCammon" <rbmccammon@ieee.org> a écrit dans le message de
news:3F233AEC.3070703@ieee.org...
Ziguy wrote:
I need to calculate the Inside to ambiant thermal resistance of a
small
plastic box filled with potted resin... How do I calculate that,
what're
the
properties needed?

As a first approximation, you can take the resin
filled box as all the same temperature and the
thermal resistance from the case to the air
will determine the box/resin temperature.

Achilles: I wish my wish would not be granted.
an undescribable event occurs
Achilles: What happened? Where's my Genie?
Tortoise: Our context got restored incorrectly.
Achilles: What does that cryptic comment mean?
Tortoise: The system crashed.


To email me send to :

rb <my last name> AT ieee DOT org

 

[John Larkin]

On Sun, 27 Jul 2003 17:44:59 -0400, "Ziguy"
<robertlatour54@hotmail.NOSPAM.com> wrote:

I was trying to do some analysis and for simplicity I used a sphere instead
of a box to calculate the thermal resistance and I came to a strange
conclusion.

The thermal resistance of a sphere is 1/(4*pi*k*r), where k is the thermal
conductivity and r is the radius of the sphere. A you can see, the thermal
resistance is inversely proportional to the radius. So it mean that if you
increase the sphere, the delta temperature between the center and the
surface of it will decrease . I would have sais the opposite, no?

The thermal resistance from "the center" of a sphere to its surface is
infinite if "the center" is a point. For a finite source, say a
smaller isothermal interior sphere of fixed size, clearly the thermal
resistance from this source to the surface increases as the outside
radius increases.

The thermal resistance from the surface of a sphere to ambient
decreases as the radius increases; this theta is about inverse with
surface area.

John

 

[DarkMatter]

On Sun, 27 Jul 2003 16:00:10 GMT, AC/DCdude17
<JerC@prontoREMOVETHISmail.com> Gave us:

Many electronic ballasts and transformers are potted
this way.

NO! Many electronic devices WERE potted that way.

Currently AFAIK, it is now a fire risk, and no longer approved.

 

[DarkMatter]

On Sun, 27 Jul 2003 15:48:13 -0700, John Larkin
<jjlarkin@highlandSNIPtechTHISnologyPLEASE.com> Gave us:

I was threatened with bodily harm when I had some machinists mill open
a bunch of potted modules for failure analysis. The silica-filled
epoxy ate up end mills at an astounding rate, and the dust gummed up
and abraded everything. Nasty stuff.

John

Hahahahahahaha... Damned shame they didn't carry it out.

I owed you that, asshole. :] Go see "Pirates"...

 

[Ziguy]

The surface area have no effect since it the thermal resistance of the
center to the surface.

"Jim Thompson" <Jim-T@analog_innovations.com> a écrit dans le message de
news:r3j8ivs28m1sku27vhhlaljataltuafpef@4ax.com...

On Sun, 27 Jul 2003 17:44:59 -0400, "Ziguy"
robertlatour54@hotmail.NOSPAM.com> wrote:

I was trying to do some analysis and for simplicity I used a sphere
instead
of a box to calculate the thermal resistance and I came to a strange
conclusion.

The thermal resistance of a sphere is 1/(4*pi*k*r), where k is the
thermal
conductivity and r is the radius of the sphere. A you can see, the
thermal
resistance is inversely proportional to the radius. So it mean that if
you
increase the sphere, the delta temperature between the center and the
surface of it will decrease . I would have sais the opposite, no?



You have more surface area so the power is spread out. But your
thermal resistance is higher.

Also, you should be using a non-point-source for the power
representation.

...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 | |
| Jim-T@analog_innovations.com Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

For proper E-mail replies SWAP "-" and "_"

Get Lolita Out of Debt... Add Three Inches to Your Mortgage!

 

[Ziguy]

Why is it infinite if the center is a point? That would mean the sphere as
no thermal conductivity, no? Also, why is the Rth increase with r if the
source is not a point? The relation Rth = 1/(4*pi*k*r) don't seam to explain
neither of your affirmation...

By the way, do you have any equations for the thermal resistance from the
surface of a sphere (or any abitrary shapes) to ambient?

I don't wan't to contradict you since I had no knowledge about thermodynamic
before yesterday. I just try to understand! Thanks for you help!

 

[John Larkin]

On Sun, 27 Jul 2003 16:43:18 -0700, DarkMatter
<DarkMatter@thebarattheendoftheuniverse.org> wrote:

On Sun, 27 Jul 2003 15:48:13 -0700, John Larkin
jjlarkin@highlandSNIPtechTHISnologyPLEASE.com> Gave us:

I was threatened with bodily harm when I had some machinists mill open
a bunch of potted modules for failure analysis. The silica-filled
epoxy ate up end mills at an astounding rate, and the dust gummed up
and abraded everything. Nasty stuff.

John


Hahahahahahaha... Damned shame they didn't carry it out.

Hey, speaking of nasty stuff, how are you these days?

John

 

[Ian Stirling]

In sci.electronics.misc Tony Williams <tonyw@ledelec.demon.co.uk> wrote:

In article <3JEUa.13731$Wh.1371784@news20.bellglobal.com>,
Ziguy <robertlatour54@hotmail.NOSPAM.com> wrote:

What is better in term of heat dissipation: A TO220 in free air
inside a closed box or a TO220 sunk in a box full of resin?

From inside, I wanted to say from the TO220 case surface! The box
is rectangular, 2.25" x 1.75" x 0.75" and will contain a 2" x
1.5" PCB.

I did a similar experiment many years ago (too many!).
300mW plastic transistors in free air, and then potted
in epoxy resin, in a plastic box about 1x1x0.4 inches.

Vbe measurements showed that the transistors required
about 4x the power to reach the same junction temperature.

Run for long enough to heat the resin through?

--
http://inquisitor.i.am/ | mailto:inquisitor@i.am | Ian Stirling.
---------------------------+-------------------------+--------------------------
All I want is a warm bed, a kind word and unlimited power -- Ashleigh Brilliant.

 

[DarkMatter]

On Sun, 27 Jul 2003 20:02:20 -0400, "Ziguy"
<robertlatour54@hotmail.NOSPAM.com> Gave us:

The surface area have no effect since it the thermal resistance of the
center to the surface.

It has an effect on the level of radiant dispersion, which effects
overall capacity to conduct heat. A bit, but there nonetheless.
So does the texture of the surface.

 

[Ian Stirling]

In sci.electronics.misc Ziguy <robertlatour54@hotmail.nospam.com> wrote:

I need to calculate the Inside to ambiant thermal resistance of a small
plastic box filled with potted resin... How do I calculate that, what're the
properties needed?

You need the thermal conductivity of the resin, and possibly the
heat capacity (if you'r not steady state)

If you are willing to spend a few moments, you can greatly improve the
thermal conductivity by adding either silicon carbide, or aluminium
oxide.
There are many other possible additives.
Ensure it's well mixed.
This does make it somewhat harder to dissasemble.

--
http://inquisitor.i.am/ | mailto:inquisitor@i.am | Ian Stirling.
---------------------------+-------------------------+--------------------------
'Where subtlety fails, we must simply make do with cream pies' -- David Brin

 

[John Larkin]

On Sun, 27 Jul 2003 20:19:15 -0400, "Ziguy"
<robertlatour54@hotmail.NOSPAM.com> wrote:

Why is it infinite if the center is a point? That would mean the sphere as
no thermal conductivity, no? Also, why is the Rth increase with r if the
source is not a point? The relation Rth = 1/(4*pi*k*r) don't seam to explain
neither of your affirmation...

By the way, do you have any equations for the thermal resistance from the
surface of a sphere (or any abitrary shapes) to ambient?

I don't wan't to contradict you since I had no knowledge about thermodynamic
before yesterday. I just try to understand! Thanks for you help!

If the space between two concentric spheres, r1 > r2 is filled with a
conductor with the resistivity rho, the resistance between the inner
and outer surfaces is

R = rho(1/r2 - 1/r1)/4*pi

so as r2 approaches zero, R becomes infinite. That's electrical, but
the thermal situation is the same.

(cribbed from http://burster.bgu.ac.il/~gedalin/problems5.pdf)

John

 

[Tony Williams]

In article <bg1k0f$1f1$4$830fa79d@news.demon.co.uk>,
Ian Stirling <root@mauve.demon.co.uk> wrote:

tonyw@ledelec.demon.co.uk> wrote:
Vbe measurements showed that the transistors required
about 4x the power to reach the same junction temperature.

Run for long enough to heat the resin through?

We ran it for days afair.

--
Tony Williams.

 

[AC/DCdude17]

X-No-Archive: Yes

DarkMatter wrote:

Many electronic ballasts and transformers are potted
this way.

NO! Many electronic devices WERE potted that way.

Currently AFAIK, it is now a fire risk, and no longer approved.

Go buy yourself a brand new fluorescent ballast if you don't believe
me. Most of them are still potted with the good old tar.

 

[DarkMatter]

On Mon, 28 Jul 2003 07:21:38 GMT, AC/DCdude17
<JerC@prontoREMOVETHISmail.com> Gave us:

X-No-Archive: Yes

DarkMatter wrote:

Many electronic ballasts and transformers are potted
this way.

NO! Many electronic devices WERE potted that way.

Currently AFAIK, it is now a fire risk, and no longer approved.

Go buy yourself a brand new fluorescent ballast if you don't believe
me. Most of them are still potted with the good old tar.

What country are you in? Do you know what potting materials are?
What you are calling tar could very well be a formulation of a potting
material that has an appearance, and even an odor like that of tar.

Tell ya what... Why don't you do a search and see if you can find
"potting tar" or call all of the suppliers of potting materials and
ask if tar is one of the available compounds.

 

[Michael Black]

Larry Hatch (lhatch@flite.net) writes:

I have a bose unit, with a output, I have that going into an RF
transmitter, to send music, XM, etc to the front room. If I go from the
video (sends DTV music) to the XM radio, I have to adjust the
input pot on the RF transmitter. Is there a simple stereo line level or
AGC circuit out there. I have enought wires and little boxes, so
smaller the better.

Thanks

Figure out which source is louder, and put an attenuator between it

and whatever you are using to switch between the sources. That way,
each source has the same audio level going into the transmitter.

Michael

 

[Gary Lecomte]

<davidca@btinternet.com> wrote in message news:<bg1m4r$pb9$1@titan.btinternet.com>...

Again, I am talking about the bar-graph circuit in
http://www.aaroncake.net/circuits/vumeter.htm

If I need to have an average response instead of a rapid
changing response, do I need to add an electrolitic
capacitor between pin 5 and ground ? If so, what value
should it be, and will it be a true average ?

You need to add a capacitor and a parallel resistor. I would suggest a
1 mfd cap and a 1 meg resistor, both in parallel from pin 5 to ground.
The bigger the cap, the slower the response.

True average depends on a lot of factors! But to average, it should
also have a resistor in series with the diode. However, Not even sure
why he put the diode in there as its Not very good rectification and
wont't work below 0.6 volts. Ideally, It Should be an Active rectifier
using an op-amp and set for averaging output.

Take care.......Gary