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Transistor breakdown voltage

R

Rudge

Jan 1, 1970
0
I need a T039 NPN transistor with an 80 volt BVceo rating such as a BC142.

My nearest stockist holds the BC141 which has a BVceo rating of 60volt.

If I buy a BC141 and test the breakdown voltage, what are the chances that
it will exceed 80volt?



I would also like to know how manufacturers make these almost identical
transistors with different voltage ratings.



Do they just make a batch of BC140s and those which exceed 80v get stamped
'BC142'?



Or do they make separate production runs for each type?



Also, do the higher voltage versions loose out on some other parameter such
as gain?



Many thanks,

Rudge
 
E

Eeyore

Jan 1, 1970
0
Rudge said:
I need a T039 NPN transistor with an 80 volt BVceo rating such as a BC142.

My nearest stockist holds the BC141 which has a BVceo rating of 60volt.

If I buy a BC141 and test the breakdown voltage, what are the chances that
it will exceed 80volt?

No idea, but specific devices are indeed selected by parameters from a general
device group by testing, so you're in with a chance.

If the yield at higher voltages was good for that batch, you may well find that
the '141 may meet a '142 spec.

What application is it used in btw ?

Graham
 
A

Arfa Daily

Jan 1, 1970
0
Rudge said:
I need a T039 NPN transistor with an 80 volt BVceo rating such as a BC142.

My nearest stockist holds the BC141 which has a BVceo rating of 60volt.

If I buy a BC141 and test the breakdown voltage, what are the chances that
it will exceed 80volt?



I would also like to know how manufacturers make these almost identical
transistors with different voltage ratings.



Do they just make a batch of BC140s and those which exceed 80v get stamped
'BC142'?



Or do they make separate production runs for each type?



Also, do the higher voltage versions loose out on some other parameter
such
as gain?



Many thanks,

Rudge
I would suspect that breakdown voltage is a 'designed in' characteristic,
and will depend on physical dimensions of the transistor structure. The
"cherry picking" that the manufacturers do is usually related to gain and
gives something like an A, B or C suffix like BC108A or BC109B. How would
the manufacturer actually test a batch for breakdown voltage, as if you take
the device to breakdown, then it is destroyed. Would the manufacturer be
prepared to stake the breakdown voltage of a production batch, on the basis
of a few tested examples ? I'm not sure that he would. It's a bit like
having tested fuses really, isn't it ?

Arfa
 
P

Pilgrim

Jan 1, 1970
0
Arfa Daily said:
I would suspect that breakdown voltage is a 'designed in' characteristic,
and will depend on physical dimensions of the transistor structure. The
"cherry picking" that the manufacturers do is usually related to gain and
gives something like an A, B or C suffix like BC108A or BC109B. How would
the manufacturer actually test a batch for breakdown voltage, as if you take
the device to breakdown, then it is destroyed. Would the manufacturer be
prepared to stake the breakdown voltage of a production batch, on the basis
of a few tested examples ? I'm not sure that he would. It's a bit like
having tested fuses really, isn't it ?

Arfa

You are right to a certain extent. However, Mfg's do sort by
breakdownvoltage. They do this with a constant current supply set at a
very low current and measure the voltage.

Chuck P.
 
E

Eeyore

Jan 1, 1970
0
Arfa said:
I would suspect that breakdown voltage is a 'designed in' characteristic,
and will depend on physical dimensions of the transistor structure. The
"cherry picking" that the manufacturers do is usually related to gain and
gives something like an A, B or C suffix like BC108A or BC109B. How would
the manufacturer actually test a batch for breakdown voltage, as if you take
the device to breakdown, then it is destroyed. Would the manufacturer be
prepared to stake the breakdown voltage of a production batch, on the basis
of a few tested examples ? I'm not sure that he would. It's a bit like
having tested fuses really, isn't it ?

You're very mistaken.

The test is done with a current limited supply and the test is for a given
leakage current.

Due to necessity (the situation was forced on me) I've had both bipolar and
mosfet devices selected very successfully for breakdown voltage.

By these guys in fact.
http://www.semelab.co.uk/

Graham
 
E

Eeyore

Jan 1, 1970
0
Pilgrim said:
However, Mfg's do sort by breakdownvoltage. They do this with a constant current
supply set at a very low current and measure the voltage.

Correct.

Graham
 
M

mike

Jan 1, 1970
0
Rudge said:
I need a T039 NPN transistor with an 80 volt BVceo rating such as a BC142.

My nearest stockist holds the BC141 which has a BVceo rating of 60volt.

If I buy a BC141 and test the breakdown voltage, what are the chances that
it will exceed 80volt?



I would also like to know how manufacturers make these almost identical
transistors with different voltage ratings.



Do they just make a batch of BC140s and those which exceed 80v get stamped
'BC142'?



Or do they make separate production runs for each type?



Also, do the higher voltage versions loose out on some other parameter such
as gain?



Many thanks,

Rudge
There are a BUNCH of issues here.
What's the actual voltage applied in the application?

Given volume discounts and inventory reduction, it's not unusual
for a vendor to use a part in an application that would do fine
with a MUCH lesser part.

Do you really care about Bvceo? That's relevant if e is really o.
Excellent metric, but sometimes not the metric you want.

If you're running it anywhere near 80V, you might wanna think
about secondary breakdown. Devices with similar text specs
can behave quite differently at high voltages.

Worry about temperature. If you're selecting breakdown voltages,
make sure you measure at temperature extremes.

One simple way to test breakdown is to put your voltmeter in series
with the power supply. IF the meter is 10megs and you have the reading
and the power supply voltage, you have enough info to calculate
the current at various voltages. If you need more current shunt
the meter with a resistor. If you try to use a current meter and the
device goes into avalanche, you've just toasted your transistor and
maybe your meter.

I don't know how they do it today, but back in the day, there were
a few "formulae" for transistors. For a given die, you ran it
across the test bed and put it in whatever bin the specs met.
If it didn't meet any, it went into the 2n3904 bin.

Whether you can up-spec a part by testing depends a lot on the
yield of that part. Some parts have high yield and they
have to ship better parts than the spec requires. But that's
not always the case. Back when I didn't know better, I tried
to select 1% resistors out of 20% for a test jig.
Turned out there was a BIG hole in the distribution that was
10% wide. 10% resistors had a big hole in the distribution
5% wide and so on. Somebody got there before me ;-)
But I fooled them, just recalculated the ratios to be
10-20% off the standard value.

mike
 
A

Arfa Daily

Jan 1, 1970
0
Eeyore said:
You're very mistaken.

The test is done with a current limited supply and the test is for a given
leakage current.

Due to necessity (the situation was forced on me) I've had both bipolar
and
mosfet devices selected very successfully for breakdown voltage.

By these guys in fact.
http://www.semelab.co.uk/

Graham

Ah, ok. I can see how that would work. Do manufacturers ( rather than
distributors like SEME) really still do this ? Seems like a lot of trouble
to go to. There are so many (hundreds of thousands ??) of transistor types
available now, I would have thought that it was possible to select one for
whatever breakdown voltages, gain, and whatever other parameters you might
require, without difficulty ? Maybe not. Thanks for the info.

Arfa
 
E

Eeyore

Jan 1, 1970
0
Arfa said:
"Eeyore" wrote


Ah, ok. I can see how that would work. Do manufacturers ( rather than
distributors like SEME) really still do this ?

Absolutely they do ! Semelab manufactures transistors too btw. They and Zetex
probably represent the entire UK semiconductor manufacturing sector.

Seems like a lot of trouble
to go to. There are so many (hundreds of thousands ??) of transistor types
available now, I would have thought that it was possible to select one for
whatever breakdown voltages, gain, and whatever other parameters you might
require, without difficulty ? Maybe not. Thanks for the info.

The Semi makers have to test the devices for function and things like gain, so
they test for loads of stuff at the same time. It's all automated.

Here's an example of what sometimes goes on with device selection.

Decades ago we were using a Motorola part, an MJ410 in a high power audio
amplifiers as a driver. The purchasing dept found the RCA410 'equivalent' at a
lower price and initial samples worked fine so we used them.

Some months later we started getting stability problems with *some* of the
RCA410s. An alert test engineer noticed that the problem parts had a specific
code stamped into the TO-3 header. It turned out that were 3 such codes in
total; C, CN, and CNX.

I sawed the lid off one of each and even a quick inspection by eye showed that
each one had a different die fitted.

RCA initially denied everything but I eventually got an admission form their
Belgian European Headquarters.

Motorola's spec on the MJ410 was quite minimal. It didn't matter to them because
they made the part all from the same line. RCA however looked at the skimpy spec
and reckoned they could fit lots of devices that failed to meet better and more
financailly worthwhile specs into their eqivalent RCA410 device spec. So they
made RCA410s from the fall-outs from 3 other product lines with widely varying
other specs (that weren't on the data sheet). Those varying 'other specs' were
what was giving us trouble.

Graham
 
R

Rudge

Jan 1, 1970
0
Eeyore said:
No idea, but specific devices are indeed selected by parameters from a general
device group by testing, so you're in with a chance.

If the yield at higher voltages was good for that batch, you may well find that
the '141 may meet a '142 spec.

What application is it used in btw ?

Graham
I want an NPN T039 or T05 driver transistor for use in an audio amplifier.
The supply rail is 75volt. Quiesent current is about 10ma I think. 1 Watt
dissipation at 25 C. The original was an RCA 39252 (which I have no data on)
or a 2N2102. They may have been selected to to work at 75volt.

Many thanks,
Rudge
 
A

Arfa Daily

Jan 1, 1970
0
Eeyore said:
Absolutely they do ! Semelab manufactures transistors too btw. They and
Zetex
probably represent the entire UK semiconductor manufacturing sector.



The Semi makers have to test the devices for function and things like
gain, so
they test for loads of stuff at the same time. It's all automated.

Here's an example of what sometimes goes on with device selection.

Decades ago we were using a Motorola part, an MJ410 in a high power audio
amplifiers as a driver. The purchasing dept found the RCA410 'equivalent'
at a
lower price and initial samples worked fine so we used them.

Some months later we started getting stability problems with *some* of the
RCA410s. An alert test engineer noticed that the problem parts had a
specific
code stamped into the TO-3 header. It turned out that were 3 such codes in
total; C, CN, and CNX.

I sawed the lid off one of each and even a quick inspection by eye showed
that
each one had a different die fitted.

RCA initially denied everything but I eventually got an admission form
their
Belgian European Headquarters.

Motorola's spec on the MJ410 was quite minimal. It didn't matter to them
because
they made the part all from the same line. RCA however looked at the
skimpy spec
and reckoned they could fit lots of devices that failed to meet better and
more
financailly worthwhile specs into their eqivalent RCA410 device spec. So
they
made RCA410s from the fall-outs from 3 other product lines with widely
varying
other specs (that weren't on the data sheet). Those varying 'other specs'
were
what was giving us trouble.

Graham
Interesting story. Just goes to show that no matter how 'reputable' a
company, you really never can tell exactly what they are up to ...

Arfa
 
M

mike

Jan 1, 1970
0
Rudge said:
I want an NPN T039 or T05 driver transistor for use in an audio amplifier.
The supply rail is 75volt. Quiesent current is about 10ma I think. 1 Watt
dissipation at 25 C. The original was an RCA 39252 (which I have no data on)
or a 2N2102. They may have been selected to to work at 75volt.

Many thanks,
Rudge
You need to give more details on the circuit. If this is the first
stage of the amplifier, it's a lot easier than if it's the "driver"
for the output stage.
If this thing goes between ground and 75V, you want WAY more than an 80V
transistor.
If it goes between +-75V, you need way more than a 150V transistor.
Unless this is a special transistor, you can't expect to get anywhere
the maximum power dissipation at anywhere near the breakdown voltage.
Take a serious look at the dynamic characteristics, peak voltages
and currents driving the capacitive load and the secondary
breakdown curves. The RCA Power Circuits manual SP-51 has
a whole chapter on this.

And worry about the power numbers too. That 25C number is a metric
that gives you some idea about what's going on. What you really
care about is the die temperature. And it's WAY more than ambient
in a small package like that.
mike
 
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