No more TO-3 regs from ST? - Page 1
Forum section: electronics / projects

author: daddario
author_rank: Regular Contributor
timestamp: June 21, 2014, 10:18:37 am
content: Hi everyone!I had started to run out of LM317K stock and yesterday decided to order a new batch.I had always used ones from ST - 317, 337, 338, 78xx, 79xx. And now it seems that they have dropped all of them - all of the datasheets have been changed in march to no longer list the TO-3 variants. TI still seems to make the 317 and its brothers, but for the price of >22 euros(Farnells list)... no thanks - the ST ones were about 7 times cheaper.So.. what's the deal with it? Had the demand really dropped so low that there was no point producing them any more?

author: Psi
author_rank: Super Contributor
timestamp: June 21, 2014, 10:20:43 am
content: I cant remember the last time i needed something in TO-3 package.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 21, 2014, 10:30:46 am
content: People still use TO3? Who knew.

author: SeanB
author_rank: Super Contributor
timestamp: June 21, 2014, 03:25:17 pm
content: Probably the only plant that still had a TO3 packing line in working condition needed a refurbishment, and they looked at the volume of TO3 versus the cost of refurb and decided to EOL the line as uneconomic. TO3 is a unique package in that it always costs more for the package than the actual chip inside it. Generally a lot more, irrespective of the design. As well the TO3P style has a very similar current and thermal characteristic, and is a lot cheaper to make as it has no need for a welding operation to fit the top can on.Motorola had a nice line with a top cap of soft aluminium, that was ultrasonically welded to the steel base.Try to find a TO66 package new these days, you will universally find that the device is only available in TO220 form, which can come preformed to fit a TO66 footprint with the centre leg cropped short.

author: daddario
author_rank: Regular Contributor
timestamp: June 21, 2014, 03:32:51 pm
content: Quote from: mikeselectricstuff on June 21, 2014, 10:30:46 amYes, the pro-audio industry, especially in broadcast, is known to have some overkill design elements. How about a power supply with MT-200 case pass transistors that dissipate some 15-20W, tops? : p

author: SeanB
author_rank: Super Contributor
timestamp: June 21, 2014, 03:37:41 pm
content: That MT 200 case style is probably a tenth of the cost to make than a TO3, and probably has better thermal performance by not needing to have 2 clearance holes for the leads. They do fit a TO3 mounting, and have a larger thermal area to transfer heat. At least they do not have that horrid tendency to bow.

author: rob77
author_rank: Super Contributor
timestamp: June 21, 2014, 04:08:40 pm
content: just for the sake of curiosity ...are you using those TO-3 devices for repairing old stuff or building new devices ?

author: daddario
author_rank: Regular Contributor
timestamp: June 21, 2014, 05:25:58 pm
content: Quote from: rob77 on June 21, 2014, 04:08:40 pmWell, both.I had planned to do another small batch of PSU's - I have this semi-universal three-rail base design that I either fit with TO-220 case LM317s with a small heatsink or populate the footprint with a 3-pin KK-series Molex connector and have TO-3 regs on a chassis mounted heatsink. It's just that I've already established a source for nice heatsinks that have the correct specifications, fit the chassis nicely, have TO-3 holes in them, etc, etc. Now I either have to change the heatsink and go for TO-220s(of which ?j-c doesn't particularly impress me) or use a separate pass transistor (either a TO-3 or still change the radiator and go for a TO-247 or something like that). But that would mean designing a new board, adding separate OCP circuitry and so on. It's all just a bit of hassle and spending time. Besides, then the design loses its beauty and simplicity, adding components that take extra board space, extra assembly time and can later fail "on the field" and so on...

author: SeanB
author_rank: Super Contributor
timestamp: June 21, 2014, 05:38:23 pm
content: TO247 or TO3P will fit the mounting still, you just crop the middle leg if it is not an isolated case style, and bend the outer 2 to fit the existing TO3 lead holes. Otherwise you just bolt it down to the back of the heatsink and use the 3 leads to connect wires, or a small piece of board with traces to fit as adaptor piece. Easier if it is an isolated device and does not need an insulating washer, just a thermal pad or grease.

author: Rufus
author_rank: Super Contributor
timestamp: June 21, 2014, 07:29:17 pm
content: Quote from: mikeselectricstuff on June 21, 2014, 10:30:46 amYeah get with the program, don't need stinking welded cans when we can make plastic parts out of ceramic, metal and glass like herehttp://products.semelab-tt.com/mil/pack_range_modern_metal.shtml