Common Practice for Transistors to be used as fuses?

A

AggieSawDust

Guest
My buddy dropped his ReplayTV off at my place the other day for me to
take a look at. It turns out that one of the power supply output pins
had a blown transistor attached to it. After further inspection, I saw
the middle leg (Base or Gate, couldn't tell what kind of transistor it
was) was cut and not connected to anything. This was apparantly done
by design since none of the other two transistors attached to output
pins had their middle legs connected to anything either.

So anyway, best I can tell, these were designed to be used as fuses
(that must make these normally closed transistors JFETs, right?). Not
being too experienced, I've never run across this. Is this a common
practice? Wouldn't it make sense to use actual fuses to make servicing
easier?

Thanks,
-Patrick
 
Sometimes transistors are used as diodes.

The middle leg, I have found, does not necessarily have to be the base. The
configuration can be EBC, but it can also be ECB or CEB, these I have seen
often among others.

Ernie


"AggieSawDust" <AggieSawDust@gmail.com> wrote in message
news:1152842789.736607.184720@75g2000cwc.googlegroups.com...
My buddy dropped his ReplayTV off at my place the other day for me to
take a look at. It turns out that one of the power supply output pins
had a blown transistor attached to it. After further inspection, I saw
the middle leg (Base or Gate, couldn't tell what kind of transistor it
was) was cut and not connected to anything. This was apparantly done
by design since none of the other two transistors attached to output
pins had their middle legs connected to anything either.

So anyway, best I can tell, these were designed to be used as fuses
(that must make these normally closed transistors JFETs, right?). Not
being too experienced, I've never run across this. Is this a common
practice? Wouldn't it make sense to use actual fuses to make servicing
easier?

Thanks,
-Patrick
Click to expand...
 
Oh, one other thing that I remembered. It's a bit OT but in the 60's many
transistors were used as diodes (the emitter-base junction), or even fakes
were soldered onto the board (not actually going anywhere) to increase
transistor count. Sure an AM radio could be built with 5 or 6 transistors,
but if you got the 12-transistor model, it just HAD to be better, right?

Ernie

"AggieSawDust" <AggieSawDust@gmail.com> wrote in message
news:1152842789.736607.184720@75g2000cwc.googlegroups.com...
My buddy dropped his ReplayTV off at my place the other day for me to
take a look at. It turns out that one of the power supply output pins
had a blown transistor attached to it. After further inspection, I saw
the middle leg (Base or Gate, couldn't tell what kind of transistor it
was) was cut and not connected to anything. This was apparantly done
by design since none of the other two transistors attached to output
pins had their middle legs connected to anything either.

So anyway, best I can tell, these were designed to be used as fuses
(that must make these normally closed transistors JFETs, right?). Not
being too experienced, I've never run across this. Is this a common
practice? Wouldn't it make sense to use actual fuses to make servicing
easier?

Thanks,
-Patrick
Click to expand...
 
On 2006-07-14, AggieSawDust <AggieSawDust@gmail.com> wrote:
My buddy dropped his ReplayTV off at my place the other day for me to
take a look at. It turns out that one of the power supply output pins
had a blown transistor attached to it. After further inspection, I saw
the middle leg (Base or Gate, couldn't tell what kind of transistor it
was) was cut and not connected to anything. This was apparantly done
by design since none of the other two transistors attached to output
pins had their middle legs connected to anything either.
Click to expand...
1 > are you sure it's a transistor,

2 > the heatsink tab of TO220 devices is connrectd to the middle pin
if the tab is connected to the circuit the middle pin is not needed.

3 > the middle pin of TO220 packaged device is not the base or gate.

Bye.
Jasen
 
On 13 Jul 2006 19:06:29 -0700, "AggieSawDust" <AggieSawDust@gmail.com>
wrote:

My buddy dropped his ReplayTV off at my place the other day for me to
take a look at. It turns out that one of the power supply output pins
had a blown transistor attached to it. After further inspection, I saw
the middle leg (Base or Gate, couldn't tell what kind of transistor it
was) was cut and not connected to anything. This was apparantly done
by design since none of the other two transistors attached to output
pins had their middle legs connected to anything either.

So anyway, best I can tell, these were designed to be used as fuses
(that must make these normally closed transistors JFETs, right?). Not
being too experienced, I've never run across this. Is this a common
practice? Wouldn't it make sense to use actual fuses to make servicing
easier?

Thanks,
-Patrick
Click to expand...
Somewhat "common practice"

The reversed biased base-emitter junction on a silicon transistor
behaves as a low power zener diode with a breakdown voltage in the 6
to 8 volt range.

2N3904 is a good candidate

Not fuses . . .

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http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
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Jasen,

I guess I'm not 100% sure it's a transistor, but it is in a TO-92
enclosure. The only thing I'm certain of is that I should be seeing no
voltage drop across this device and each leg should show 12V with
respect to ground (the other two behave like this).

So if this indeed a transistor, anyone have a favorite replacment?

-Patrick

jasen wrote:
On 2006-07-14, AggieSawDust <AggieSawDust@gmail.com> wrote:
My buddy dropped his ReplayTV off at my place the other day for me to
take a look at. It turns out that one of the power supply output pins
had a blown transistor attached to it. After further inspection, I saw
the middle leg (Base or Gate, couldn't tell what kind of transistor it
was) was cut and not connected to anything. This was apparantly done
by design since none of the other two transistors attached to output
pins had their middle legs connected to anything either.

1 > are you sure it's a transistor,

2 > the heatsink tab of TO220 devices is connrectd to the middle pin
if the tab is connected to the circuit the middle pin is not needed.

3 > the middle pin of TO220 packaged device is not the base or gate.

Bye.
Jasen
Click to expand...
 
By replacement, since I don't have a recognizable part number to share,
does anyone know of a good transistor that can be used as a 1.5 A fuse
(based on writing on the circuit board)?


AggieSawDust wrote:
Jasen,

I guess I'm not 100% sure it's a transistor, but it is in a TO-92
enclosure. The only thing I'm certain of is that I should be seeing no
voltage drop across this device and each leg should show 12V with
respect to ground (the other two behave like this).

So if this indeed a transistor, anyone have a favorite replacment?

-Patrick

jasen wrote:
On 2006-07-14, AggieSawDust <AggieSawDust@gmail.com> wrote:
My buddy dropped his ReplayTV off at my place the other day for me to
take a look at. It turns out that one of the power supply output pins
had a blown transistor attached to it. After further inspection, I saw
the middle leg (Base or Gate, couldn't tell what kind of transistor it
was) was cut and not connected to anything. This was apparantly done
by design since none of the other two transistors attached to output
pins had their middle legs connected to anything either.

1 > are you sure it's a transistor,

2 > the heatsink tab of TO220 devices is connrectd to the middle pin
if the tab is connected to the circuit the middle pin is not needed.

3 > the middle pin of TO220 packaged device is not the base or gate.

Bye.
Jasen
Click to expand...
 
"AggieSawDust" <AggieSawDust@gmail.com> wrote in message
news:1152901418.604059.254330@h48g2000cwc.googlegroups.com...
By replacement, since I don't have a recognizable part number to share,
does anyone know of a good transistor that can be used as a 1.5 A fuse
(based on writing on the circuit board)?


It's an IC protector, Just a fuse in a TO-92 package. Read about them
Click to expand...
here....Paul


http://www.repairfaq.org/REPAIR/F_audiofaq8.html#AUDIOFAQ_001
 
On 2006-07-14, AggieSawDust <AggieSawDust@gmail.com> wrote:
By replacement, since I don't have a recognizable part number to share,
does anyone know of a good transistor that can be used as a 1.5 A fuse
(based on writing on the circuit board)?
Click to expand...
maybe it's a fuse in a to92 package.

possibly the writing doesn't match with reality.

Bye.
Jasen
 
How can there be a fuse in a TO-92 package? You need a class tube otherwise
there will be no air for the wire to be in. A fuse can't work if it's solid




"jasen" <jasen@free.net.nz> wrote in message
news:2f6b.44b879dd.20b2a@gonzo.homenet...
On 2006-07-14, AggieSawDust <AggieSawDust@gmail.com> wrote:
By replacement, since I don't have a recognizable part number to share,
does anyone know of a good transistor that can be used as a 1.5 A fuse
(based on writing on the circuit board)?


maybe it's a fuse in a to92 package.

possibly the writing doesn't match with reality.

Bye.
Jasen
Click to expand...
 
On 2006-07-15, GeorgeDubyaRulez! <none@noemailaddress.big> wrote:
How can there be a fuse in a TO-92 package? You need a class tube otherwise
there will be no air for the wire to be in. A fuse can't work if it's solid
Click to expand...
fuses don't need air or even empty space - some are filled with sand.

some look like resistors.

Bye.
Jasen
 
its common to use transistors as a diode or diode(s) never seen them used as
fuse

base to collector on a power transistor makes a fine power diode....

DR EE


"AggieSawDust" <AggieSawDust@gmail.com> wrote in message
news:1152842789.736607.184720@75g2000cwc.googlegroups.com...
My buddy dropped his ReplayTV off at my place the other day for me to
take a look at. It turns out that one of the power supply output pins
had a blown transistor attached to it. After further inspection, I saw
the middle leg (Base or Gate, couldn't tell what kind of transistor it
was) was cut and not connected to anything. This was apparantly done
by design since none of the other two transistors attached to output
pins had their middle legs connected to anything either.

So anyway, best I can tell, these were designed to be used as fuses
(that must make these normally closed transistors JFETs, right?). Not
being too experienced, I've never run across this. Is this a common
practice? Wouldn't it make sense to use actual fuses to make servicing
easier?

Thanks,
-Patrick
Click to expand...
 
"Dleer" <drennie@cfl.rr.com> wrote in message
news:pxsug.6169$47.2279@tornado.tampabay.rr.com...
its common to use transistors as a diode or diode(s) never seen them used
as fuse

base to collector on a power transistor makes a fine power diode....

DR EE
Click to expand...

Sure not emitter-base junction? That give a definite 0.7V drop.



"AggieSawDust" <AggieSawDust@gmail.com> wrote in message
news:1152842789.736607.184720@75g2000cwc.googlegroups.com...
My buddy dropped his ReplayTV off at my place the other day for me to
take a look at. It turns out that one of the power supply output pins
had a blown transistor attached to it. After further inspection, I saw
the middle leg (Base or Gate, couldn't tell what kind of transistor it
was) was cut and not connected to anything. This was apparantly done
by design since none of the other two transistors attached to output
pins had their middle legs connected to anything either.

So anyway, best I can tell, these were designed to be used as fuses
(that must make these normally closed transistors JFETs, right?). Not
being too experienced, I've never run across this. Is this a common
practice? Wouldn't it make sense to use actual fuses to make servicing
easier?

Thanks,
-Patrick
Click to expand...
 
Based on the info from this link, I've determined that my part in
question is definitely an IC protector. I even looked at the board
again and saw the part's notation: PR102. Thanks for the assistance.
In all my education, I've never seen or even heard of these. I guess
nothing can take the place of good old-fashioned experience!

My next question is, who sells these? My local parts peddlers don't
carry them.


catguy wrote:
"AggieSawDust" <AggieSawDust@gmail.com> wrote in message
news:1152901418.604059.254330@h48g2000cwc.googlegroups.com...
By replacement, since I don't have a recognizable part number to share,
does anyone know of a good transistor that can be used as a 1.5 A fuse
(based on writing on the circuit board)?


It's an IC protector, Just a fuse in a TO-92 package. Read about them
here....Paul


http://www.repairfaq.org/REPAIR/F_audiofaq8.html#AUDIOFAQ_001
Click to expand...
 
"AggieSawDust" <AggieSawDust@gmail.com> wrote in message
news:1153096316.126235.9890@i42g2000cwa.googlegroups.com...
Based on the info from this link, I've determined that my part in
question is definitely an IC protector. I even looked at the board
again and saw the part's notation: PR102. Thanks for the assistance.
In all my education, I've never seen or even heard of these. I guess
nothing can take the place of good old-fashioned experience!

My next question is, who sells these? My local parts peddlers don't
carry them.


catguy wrote:
"AggieSawDust" <AggieSawDust@gmail.com> wrote in message
news:1152901418.604059.254330@h48g2000cwc.googlegroups.com...
By replacement, since I don't have a recognizable part number to share,
does anyone know of a good transistor that can be used as a 1.5 A fuse
(based on writing on the circuit board)?


It's an IC protector, Just a fuse in a TO-92 package. Read about them
here....Paul


http://www.repairfaq.org/REPAIR/F_audiofaq8.html#AUDIOFAQ_001
Click to expand...
Mouser has a resettable protector.....Paul

http://www.mouser.com/catalog/626/443.pdf
 
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