LM355 Replacement?
LM355 Replacement?
(OP)
Hi everybody!
I'm looking for a part that is a direct replacement for an LM355 Temperature sensor. The reason we need to replace it is because it's too big, the part is fitted into an aluminum tube, which is 4.5mm in diameter and the SMT part is too big also(we've been using these for 10 years and now the tube has shrunk!!! and we are stuck with $10k worth!!
I've had a look and can find a couple of temperature sensors but they have different output characteristics. I was thinking of a SOT23 part fitted on a PCB but I'm really struggling to find one.
Can anybody else??
Thanks
Andy
I'm looking for a part that is a direct replacement for an LM355 Temperature sensor. The reason we need to replace it is because it's too big, the part is fitted into an aluminum tube, which is 4.5mm in diameter and the SMT part is too big also(we've been using these for 10 years and now the tube has shrunk!!! and we are stuck with $10k worth!!
I've had a look and can find a couple of temperature sensors but they have different output characteristics. I was thinking of a SOT23 part fitted on a PCB but I'm really struggling to find one.
Can anybody else??
Thanks
Andy





RE: LM355 Replacement?
So what is the ID you're battling with?
Keith Cress
kcress - http://www.flaminsystems.com
RE: LM355 Replacement?
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If we learn from our mistakes I'm getting a great education!
RE: LM355 Replacement?
In any case, presumably you are referring to the LM35 in TO-92 configuration, with its nominal .18 inch o.d. plastic shell (LM35D or similar): your options are to bore out the end of the tube, or rebore the whole tube, or create a lathe chuck to hold the leads of the sensor whilst machining away some of the plastic overmold, until the parts fit. Nobody makes an equivalent temp. sensor in a different package.
I've made tubular sensors using these or their sister (the LM34 sensor) before, and have always had to allow for variations in the actual package o.d. It looks like, from the National website, that the package underwent a redesign in 2000...funny that you didn't catch the change until now.
RE: LM355 Replacement?
The datasheet shows an S0-8 SMT package which is too big.
This tube we use is 4.5mm inner diameter and the length is 100mm, so a small pcb could fit in there, If there isn't a direct replacement then maybe a small op-amp and a transistor(the base emitter voltage reacts to temperature(I think)) will acheive what I need?????
Thanks for the replys people :)
RE: LM355 Replacement?
The LM35 can be purchased in die form.
TTFN
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RE: LM355 Replacement?
These packages are for LM35?
Can you post the link please
Thanks
Andy
RE: LM355 Replacement?
When you say die form what do you mean?
RE: LM355 Replacement?
And, perhaps you should tell us what characteristics you actually need.
TTFN
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RE: LM355 Replacement?
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If we learn from our mistakes I'm getting a great education!
RE: LM355 Replacement?
Thought so.
"The datasheet shows an S0-8 SMT package which is too big."
Yes. So that package won't fit, never could fit, would be the completely wrong package to try and stuff into a 4.5 mm tube. ... But, the TO-92 package is also an option for the LM35 sensor, and that package has an o.d. not much bigger than .19 inches, or 4.8mm. When I said no other package is available, I meant that no package with a dimension smaller than the TO-92 is available for the LM35, and no equivalent sensor is available either, in any package.
"This tube we use is 4.5mm inner diameter and the length is 100mm, so a small pcb could fit in there, "<snip>
Yes. So, you bought a tube that's too small on the i.d. to fit the new TO-92 package dimensions for the LM-35. 4.8mm id for the tube would've worked nicely I'd bet. So, drill out the end of the tubes to .20 (4.9mm) i.d. for a depth of about .25 inches (6.4mm), solder leads > 100mm to the sensor, and feed the leads thru the tube (starting from the bored-out end), then stuff the sensor body into the bored section. Pot with sticky stuff of your choice, and march onwards. That's option #1, and what I would consider the cheapest option (but that's just my opinion). Option 2 is buy 4.9 mm i.d. tubing, and scrap the stuff you have. Option 3 is whittling the o.d. of the TO-92 package to fit 4.5mm i.d. tubing (expect to scrap a fair number of sensors that you cut into the underlying silicon). Option 4 is to buy bare die as suggested by others, and the production equipment to solder leads onto the tiny, tiny, lead pads on those bare chips, and hold the chips in place during potting/overmolding...
I once considered option #4, but the designer of the chip at National convinced me otherwise. If you don't believe me, call or write to Mr. Pease yourself, he's quite a nice gentleman and likes to support dumb geeks like us. He's also as nice/funny in person (via phone) as he is in his articles in the trade pubs.
Your choice.
RE: LM355 Replacement?
http://www.wirebonders.com/images/2460.jpg
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If we learn from our mistakes I'm getting a great education!
RE: LM355 Replacement?
Nonetheless, the OP hasn't really indicated why the other National temp sensors wouldn't work in his application. Given that the other devices require zero post-procurement work, I'd seriously revisit the requirements and see if there's a different way to skin that cat, rather than going into the wirebonding and/or hybridization business.
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: LM355 Replacement?
Electric planer. Works every time.
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If we learn from our mistakes I'm getting a great education!
RE: LM355 Replacement?
D.H.