LM317 LM337 TO220 - thin metal tab - diyAudio
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Old 5th September 2015, 09:46 AM   #1
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Default LM317 LM337 TO220 - thin metal tab

I lately bought some LM317 and LM337, On Semi 1.5V from Digikey. The LM337 came with the "standard" metal tab, but the LM317 came with a very thin metal tab, so thin that my TO220 insulating washers won't work with it.

Since I could not mount them on the heatsink properly I thought I wasted my parts.

I then ordered them again, this time National Semi 1.5V from Farnell. It got worse. Both the LM337 and LM317 came with the very thin metal tab.

I started using LM317 and LM337 more than 10 years ago and have ordered them quite a few times. They all came with standard ones. But the last 2 times they came with very thin metal tab.

This forced me to examine the datasheet more carefully and I now understand that there are "single gauge" / thin metal tab of 0.51-0.61mm thickness and "dual gauge" of 1.41 - 1.61mm thickness.

But I just can't find how this information is available through the part numbers or through the part descriptions. This metal tab thickness is never listed as a parameter in Digikey's or Farnell's part descriptions.

Can you shed some lights? I now need to find out how to order the LM317 and LM337 with thick metal tab, or go and find the thin insulating washers.
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Old 5th September 2015, 11:37 AM   #2
sangram is offline sangram  India
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You could always use nylon screws or clamping bars if you wanted more or less mounting pressure and not have to worry about insulating the mounting hole...

I find a small piece of heatshrink tube and a standard flat nylon washer work just as well as a shoulder washer, along with some glue. Unfortunately this is rather a permanent assembly (including the bolt) and can only be used as a set hereon out.

Finally, if you are not dissipating much heat, heat transfer tape works quite well up to about half a watt and requires no extra hardware.
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Old 5th September 2015, 11:52 AM   #3
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From TI's datasheet the -KCT suffix is the new thin (0.5mm) tab and -KCS the old, traditional 1.2mm thick version.
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Old 5th September 2015, 12:33 PM   #4
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Quote:
Originally Posted by sangram View Post
You could always use nylon screws or clamping bars if you wanted more or less mounting pressure and not have to worry about insulating the mounting hole...

I find a small piece of heatshrink tube and a standard flat nylon washer work just as well as a shoulder washer, along with some glue. Unfortunately this is rather a permanent assembly (including the bolt) and can only be used as a set hereon out.

Finally, if you are not dissipating much heat, heat transfer tape works quite well up to about half a watt and requires no extra hardware.
Oh, of course, nylon screws would work. How didn't I think of it?
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Old 5th September 2015, 12:35 PM   #5
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Originally Posted by abraxalito View Post
From TI's datasheet the -KCT suffix is the new thin (0.5mm) tab and -KCS the old, traditional 1.2mm thick version.
Thanks for that. Interestingly, the National datasheet did not even mention it. I will probably find some nylon screws and if not look for the KCS.
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Old 5th September 2015, 12:38 PM   #6
AndrewT is offline AndrewT  Scotland
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Nylon.
Think about creep and particularly how creep is dependent on temperature.
Creep = change in dimension while under stress.
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Old 5th September 2015, 12:40 PM   #7
AndrewT is offline AndrewT  Scotland
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I cut down the length of the top hat to suit the thickness to be secured.
A sharp knife slices through the thin collar very easily.
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Old 6th September 2015, 12:29 AM   #8
Enzo is offline Enzo  United States
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agree^^^^

I often find the shoulder washers in my drawer are for a deeper hole than I have, so I poke it through the tab, and trim off the excess length with my Xacto knife.
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Old 6th September 2015, 01:10 AM   #9
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So nylon is not good because it is not suitable for higher temperature?

I have tried to cut the washer thinner but was not successful. I will try it again.
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Old 6th September 2015, 01:52 AM   #10
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TIP transistors now come with a thin metal tab.

If you are using a heat sink it shouldn't make a diff, but I haven't measured. I would imagine that the thicker tab absent a heatsink would have some thermal hysteresis.
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