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Topic: suggest an NPN not afffected by temperature? (Read 3373 times) previous topic - next topic

db2db

Nov 14, 2014, 05:20 am Last Edit: Nov 14, 2014, 05:21 am by db2db
I'm looking for a NPN BJT (SOT23) that has a pretty stable VBE as the temperature changes.
I was told that the Fairchild 2N5088BU is good, but I see no supporting data.

Any suggestions??

weedpharma

What temperature range are you looking for?

Henry_Best

#2
Nov 14, 2014, 06:55 am Last Edit: Nov 14, 2014, 06:56 am by Henry_Best
What temperature range are you looking for?
Over about 300oC, ALL transistors are affected.   :smiley-mr-green:

weedpharma

I had considered a range from 0 deg K as starting point. :smiley-mr-green:

Weedpharma

JimboZA

0 deg K
Bzzzzzzt.

Temperatures on the Kelvin scale are not named "degrees", they're just "Kelvin", as in "0 Kelvin".
Johannesburg hams call me: ZS6JMB on Highveld rep 145.7875 (-600 & 88.5 tone)
Dr Perry Cox: "Help me to help you, help me to help you...."
Your answer may already be here: https://forum.arduino.cc/index.php?topic=384198.0

weedpharma

Bzzzzzzt.

Temperatures on the Kelvin scale are not named "degrees", they're just "Kelvin", as in "0 Kelvin".
Mea culpa

TomGeorge

Hi, what is the application that you need a transistor with this characteristic, there may be another way of accomplishing what you need.

Tom......... :)
Everything runs on smoke, let the smoke out, it stops running....

MarkT

All silicon transistors have the same dependency on temperature, there's nothing you
can do by choosing a better device.

What you can do is use a cancelling circuit to subtract the temperature dependence by
using two matched transistors kept at the same temperature.  You keep a constant
current through one and then the Vbe difference cancels out.

You can also choose a semiconductor with a much higher bandgap voltage, as the
thermal term subtracts from this, so the larger the bandgap the less the thermal
term proportionally.  That means gallium arsenide, silicon carbide or other exotic/expensive
devices.

But unless you say what you are trying to achieve its hard to know how to help.
The cancellation circuit is useful for making analog logarithmic amplifiers and
multipliers, for instance.

It might be that you need feedback in your circuit to linearise it, there are many ways
round a problem if you know the actual goal.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

cjdelphi

It's possible to turn a transistor or even a diode into a temperature sensor based on it's forward voltage drop..

How's Germanium hold out over silicon?  Better  / worse regarding temperature?

db2db


Thanks for the answers. I didn't realize all equally temp sensitive.

TomGeorge

Hi,please read post #7, what is the application, what are you going to do with a transistor if you could  find one?

Tom.. trying to help! ! ! ..... :)
Everything runs on smoke, let the smoke out, it stops running....

Paul__B

#11
Nov 15, 2014, 08:49 am Last Edit: Nov 15, 2014, 08:51 am by Paul__B
As always - you should explain what your actual problem is that you need to address, not what you have imagined as the solution to the problem.

Grumpy_Mike


db2db


I am using it in a feedback circuit for a constant current driver. I have some other solutions in mind, so don't need more info.. yet.

Thanks.

Paul__B

That's good, because unless you describe it in more detail - in fact a lot more detail, explanation and specifics including current and proposed circuitry - you are not going to get much useful assistance.  :smiley-grin:

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