My TO-3 switcher (buck converter) - Page 1
Forum section: electronics / projects

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: July 17, 2015, 02:22:31 am
content: In order to reduce the heat dissipated by vintage computers and other digital electronics equipped with TO-3 linear regulators, I decided to embark on a little project. I sent out the artwork to OSH Park three weeks ago and just got the boards tonight.I wanted to get as close as possible to the original form factor with regards to the contacts, I picked the Mill-Max 8979-0-00-15-00-00-03-0 and used the suggested hole size.http://www.digikey.ca/product-detail/en/8979-0-00-15-00-00-03-0/ED1114-ND/3516739Whacking it in gently with a light hammer gives a pleasing result.I don't know how this will hold up over time and thermal cycles. It *feels* solid enough. I still feel like flowing some HMP solder over the whole thing just to be sure but I was warned against this here, although never told why exactly.Gonna be a rainy w/e apparently, I'll finish simulating the loop filter and pick values, the goal is a 5V output at a fairly steady 500mA load, no big transients. No, I don't know why Commodore picked such enormous regulators for such a light load back then. They heat up because the input voltage is fairly high. I don't know why either.

author: fivefish
author_rank: Frequent Contributor
timestamp: July 17, 2015, 03:54:06 am
content: This is awesome... following.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: July 17, 2015, 05:13:47 am
content: ::thumbsup!::I suspect they just had a lot of them. Pulled the same stunt on the VIC-20 and on the PET they needed a pair of them...

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 17, 2015, 05:45:22 am
content: SexyDid you manage to get the filtering you wanted, in the end?

author: SeanB
author_rank: Super Contributor
timestamp: July 18, 2015, 10:35:22 am
content: TO3 was used because back then a 5V regulator was only available in the TO3 package, the alternative was to use a discrete regulator with transistors and a LM723 regulator, or a 5V6 zener and a pass transistor. Only later did you get a plastic packaged TO220 device, and those were initially also as expensive as the TO3 package, which was at the time a mass produced package and thus cheap.

author: LukeW
author_rank: Frequent Contributor
timestamp: July 18, 2015, 10:44:44 am
content: Beautiful work.So, OSHPark doesn't have a design rule issue with copper extending all the way to the board edge?I'll have to find where to turn off that DRC parameter in Eagle to let the copper extend all the way to the board edge.I love the board curved edge in a perfect TO-3 shape, too.

author: codeboy2k
author_rank: Super Contributor
timestamp: July 18, 2015, 03:12:33 pm
content: That's way cool !Great work by you, and definitely deserving of a nice board from OSH Park.Keep us posted on the performance tuning results.

author: fcb
author_rank: Super Contributor
timestamp: July 18, 2015, 03:23:49 pm
content: Very nice work Alex and a great idea.

author: zapta
author_rank: Super Contributor
timestamp: July 18, 2015, 05:12:49 pm
content: Looks very nice. You can 3D print a matching cover.

author: calexanian
author_rank: Super Contributor
timestamp: July 18, 2015, 05:58:17 pm
content: I love it. Brilliant!As for why they used them. My guess would just be that they are a well known part that was commonly avaliable. Simple as that. Space was not a real concern over reliability. I alse recall Commodore had some power supply heating problems at some point early on and it gave them a black eye. Perhaps this is a "Well, we will make sure that never happens again" solution.

author: calexanian
author_rank: Super Contributor
timestamp: July 18, 2015, 06:04:20 pm
content: Oh, totally forgot to answer your question! As far as the thermo cycling of the pins and their longevity, I would follow up with some leaded solder with real RA rosin flux. Gold to Gold joints can become problematic in this kind of use I have found. Kester 44 is the best for this application. Just deflux it really well. The lead gives a joint that has far more compliance, and be sure to flow both sides of the joint or stress fractures may occur.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: July 19, 2015, 05:10:34 pm
content: Wow thanks for the positive comments everyone!It rained Friday night, so I started putting parts on one board, then it didn't rain Saturday so I didn't work on it. Summer realistically lasts about 6 weeks here, so I spend as much as possible outside.Today is bike maintenance day...

author: SeanB
author_rank: Super Contributor
timestamp: July 19, 2015, 05:21:10 pm
content: Summer here lasts all year round. I went up on the roof to do some cleaning and inspection. Waited till noon when it was 24C, was too cold in the morning at 12C. I used to go swimming in the sea all year round, but in winter I would use a thin wetsuit because 12C water felt cold. The surfers go in all year round.

author: marshallh
author_rank: Unknown
timestamp: July 19, 2015, 05:24:12 pm
content: Oshpark doesn't have any rules about coppter to pcb outline. In fact you can make the mill cut through the copper (not recommended).

author: MagicSmoker
author_rank: Super Contributor
timestamp: July 19, 2015, 09:38:31 pm
content: I also want to chime in, mainly to say this is totally awesome if a bit on the impractical/outlandish side (but that just makes it more awesome, really)!As for attempting to duplicate the TO-204 (nee TO-3) package, you might want to try decapping a real TO-3 part (Dremel, maybe?) then removing the die inside with a hot air pencil to reflow the die attach solder. Cut off the bondwires to the pins and you'll have all the mechanical bits sorted. Finally - and apologies for pointing out the obvious, here - you don't necessarily need to put the cap back on the TO-3 package. In fact, I'd say it would be a lot cooler to leave it off.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: July 24, 2015, 03:21:32 am
content: Soldered on all the parts. Skipped all the caution and plugged it directly to a 9V DC in and a 10R load. Works great.Load is hot, Ton3y (that's what I call the regulator now) is barely warmer than ambient, as measured by the back of my pinkie.The in and out filters are 1uH 1A coils with the various capacitors on Ton3y.It's a bit bigger than I wanted, serves me right for using a 1960s JEDEC drawing... Oh well.It didn't blow up, it's been running for hours, if it rains I'll do some more in-depth tests on the w/e.Quote from: SeanB on July 19, 2015, 05:21:10 pmI can already see the sun setting earlier and I get the sun in my eyes when I bike home... I can feel fall in the air.Quote from: zapta on July 18, 2015, 05:12:49 pmThe thought occurred. I want to make a clip-on doodad with a Commodore logo on it. Maybe.Quote from: T3sl4co1l on July 17, 2015, 05:45:22 amA quick look with the scope shows about 60mV of noise on the output. Good enough for TTL work...

author: Mr.B
author_rank: Unknown
timestamp: July 24, 2015, 03:38:05 am
content: Very impressive.Well done!

author: LukeW
author_rank: Frequent Contributor
timestamp: July 24, 2015, 08:31:47 am
content: Actually I think OSHPark does have a 15 thou copper-to-edge rule.But it looks like they will violate that, it's more a like a "don't blame us if fine signal traces on the edge get severed" issue so it's not so critical on a groundplane.

author: SeanB
author_rank: Super Contributor
timestamp: July 25, 2015, 09:24:13 am
content: Quote from: Alex Eisenhut on July 24, 2015, 03:21:32 amI have seen more than that on a regular LM340K regulator......... Some LDO regulators will happily oscillate at around 2MHz with the right combination of input voltage, load and capacitance.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: July 25, 2015, 01:05:47 pm
content: Quote from: SeanB on July 25, 2015, 09:24:13 amThen there's probably more noise than that.... I used my old Rigol beater, I wanted to use my 1A5 differential plugin but only when I have a more solid setup.Here's a picture of my super high tech test setup...

author: SeanB
author_rank: Super Contributor
timestamp: July 25, 2015, 01:50:09 pm
content: With that setup most linear regulators will become happy oscillators.........Your switcher is a lot more forgiving of poor application than the garden variety regulator, you basically made a very nice drop in regulator replacement, which both looks nice and performs as good or even better than the original. You probably could do a few hundred of them on Ks and sell them as a near drop in replacement.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: July 25, 2015, 03:54:10 pm
content: Quote from: SeanB on July 25, 2015, 01:50:09 pmI know, I sprinkled some large caps on the input and output. Plus I'm feeding in a regulated voltage too... What I mean by solid setup is I'm going to bolt it in a 1541 and run it there.Drop in switchers in to-220 packages are already available, I basically just put one on my layout. I don't think there is a KS in Canada. But the loonie (cdn $) is in the toilet, I might be able to make money just on the exchange rate.Plus I'm thinking of re-spinning it with a AOZ1051 chip, half the cost, synchronous, 3A, but has a thermal pad. I think that's not too bad to hand-solder. I picked the TI chip because it's in a straight SO-8 package.

author: Tachyon
author_rank: Newbie
timestamp: July 26, 2015, 05:07:40 am
content: This is a very cool project. I know some people will give the old "why not just buy something newer and use that instead?" comment, but I totally get this.In fact, I've been trying to get members of the retro-computing community to organize and collaborate on projects just like this. So that we can reverse engineer and document irreplaceable or hard/expensive/impractical to replace components like for example your regulator, or a Commodore PLA, and then work together to create open designs for replacements. Right now I'm focussing on the Commodore community, but in the future I would hope others would join in to organize for other platforms.It's been exciting to see how many people are already doing projects like this. I'd just like to see us all centralize and organize a place to tie it all together while making use of existing resources like EEVblog, Lemon64, Lemon Amiga, etc.Anyway, congrats on a fine looking project, and on reviving that 1541. Please let us know if you make the project available, even if it's as an OSHPark file and a BOM.

author: SeanB
author_rank: Super Contributor
timestamp: July 26, 2015, 07:45:18 am
content: That new switcher looks nice, you probably could also add extra pads for the feedback side to make a drop in replacement for a 5V, 8V and 12V regulator, or just put the bottom resistor of the divider near the side so it is easy to change out to adjust. Bottom resistor so it defaults to 0.8V if it goes open circuit.

author: fcb
author_rank: Super Contributor
timestamp: July 26, 2015, 08:35:00 am
content: I'd buy one just to sit on the shelf!

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: July 26, 2015, 12:28:01 pm
content: Quote from: SeanB on July 26, 2015, 07:45:18 amYes, the pads for L1 are oversized for other output inductors, and changing the voltage is just a question of changing feedback resistors.But the 12V has transient loads; the floppy motor and head stepper. That's where the compensation loop will probably need to be tweaked too.Quote from: fcb on July 26, 2015, 08:35:00 amA 1541 or a Ton3y? I have two other boards! And it looks like KS has a Canadian section now. I don't know if there's this enormous TO-3 market though. Jewellery, eh?

author: BravoV
author_rank: Super Contributor
timestamp: July 26, 2015, 12:33:39 pm
content: Quote from: Alex Eisenhut on July 26, 2015, 12:28:01 pmThe audiophools herd, once they're picking up, you could be ended with filthy rich.

author: emc-problem.net
author_rank: Newbie
timestamp: July 26, 2015, 05:01:19 pm
content: Well work.This is awesome!!!

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: July 26, 2015, 05:29:25 pm
content: Quote from: emc-problem.net on July 26, 2015, 05:01:19 pm? O0

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 26, 2015, 07:19:05 pm
content: "Good work"?

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: July 26, 2015, 07:45:59 pm
content: Quote from: Alex Eisenhut on July 26, 2015, 05:29:25 pmOh, weird, the Cyrillic characters just get zapped? Oh well. Spasibo, I guess?

author: babysitter
author_rank: Frequent Contributor
timestamp: July 27, 2015, 05:36:34 am
content: You have beean HackADayed!

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: July 27, 2015, 11:57:45 am
content: Quote from: babysitter on July 27, 2015, 05:36:34 amAh, that explains the explosion of views. I also see that there is a previous to-3 switcher out there. Great minds, I guess...

author: TiN
author_rank: Super Contributor
timestamp: July 27, 2015, 12:08:09 pm
content: Great idea, thumbs up :-)

author: AccountRemovedPerUsersRequest
author_rank: Regular Contributor
timestamp: August 02, 2015, 05:34:35 am
content: Quote from: Tachyon on July 26, 2015, 05:07:40 amSecond that. Even if you're not publishing the project the schematic and/or BOM would be interesting to see. Just built a small size dc/dc converter myself...Axel.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: August 04, 2015, 01:26:43 am
content: Well the schematic is just the TI circuit from the datasheet. I ain't no EE genius over here. I just calculated the coil value, added some filtering, a fuse, and the layout. Oooh and I picked those Mill-Max pins. O0The regulator is working in a 1541, and there are no problems.I'll take some waveforms and post them, as soon as the weather sucks.

author: AccountRemovedPerUsersRequest
author_rank: Regular Contributor
timestamp: August 04, 2015, 05:43:07 am
content: Quote from: Alex Eisenhut on August 04, 2015, 01:26:43 amCould you tell which chip you used? (I think I didn't catch the information)Axel.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: August 04, 2015, 11:42:40 am
content: It's the TPS54232.

author: Kjelt
author_rank: Super Contributor
timestamp: August 04, 2015, 11:58:28 am
content: Very nice project, well done. Now a nice looking cap on top and heat conducting potting material and finishedI thought there was a TO3 7805 that was rated for 5 Amps or am I mistaken?

author: rdl
author_rank: Super Contributor
timestamp: August 04, 2015, 12:24:38 pm
content: Quote from: Kjelt on August 04, 2015, 11:58:28 amI'm pretty sure there was. I also seem to remember there was one company that made a TO-3 5 volt regulator that went to 10 amps, it had a different number from 7805 though. I have an LM338K in a TO-3 rated for 5 amps in my parts collection.

author: Monkeh
author_rank: Super Contributor
timestamp: August 04, 2015, 01:16:41 pm
content: Quote from: rdl on August 04, 2015, 12:24:38 pmLT1038 comes to mind.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: August 05, 2015, 03:37:13 am
content: Quote from: Kjelt on August 04, 2015, 11:58:28 am78H05

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: August 05, 2015, 03:42:27 am
content: Quote from: AcHmed99 on August 04, 2015, 01:34:03 pmTon3y can safely source 1A with 9V DC in. The TPS chip is rated to 2A, and I think it can do it if I review the inductor selection. The weak point is the thermal design, I should have put more thermal vias around the diode too.I will likely re-spin with a higher-rated part and put more thermal vias.

author: technix
author_rank: Super Contributor
timestamp: August 05, 2015, 04:02:44 am
content: You can put a bit of solder on the component side to old the pins down firmly.

author: LabSpokane
author_rank: Super Contributor
timestamp: August 05, 2015, 05:22:04 am
content: Quote from: LukeW on July 18, 2015, 10:44:44 amNope. And you could just download Laen's design rules. I have run copper to the edge on a couple boards and it's been fine.

author: tree
author_rank: Regular Contributor
timestamp: August 05, 2015, 03:35:07 pm
content: Neat project. I sure do love the TPS54xxx datasheets. They are very well written with tons of design equations that result in good enough starting values for designers.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: August 11, 2015, 11:38:52 pm
content: If anyone is still reading, I'm building up the 12V version and will try a Commodore 1541 with two Ton3ys in it.Soon.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: September 29, 2015, 11:38:34 pm
content: Wow, time flies. Well, it is just a regulator, and they work pretty well so far.The rightmost one is the 5V version with extra output capacitance, and the 12V one is for driving the motors, the output can be noisier.The 1541 runs quite cool.

author: AF6LJ
author_rank: Unknown
timestamp: September 29, 2015, 11:53:25 pm
content: This is one fo the best things I have seen come along in a long time.I am also following. Great

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: September 30, 2015, 12:26:18 am
content: Quote from: AF6LJ on September 29, 2015, 11:53:25 pmThanks, it looks good but the fatal flaw is that now that the input side needs less current, the voltage on the smoothing capacitors rises and they are running close to their rated voltage. Don't know how great that is for 30 year old electrolytics. So the lifetime I might gain by running cooler I'll lose by running those capacitors too close to their rated voltage.

author: AF6LJ
author_rank: Unknown
timestamp: September 30, 2015, 03:52:09 am
content: Quote from: Alex Eisenhut on September 30, 2015, 12:26:18 amNew electrolytics wouldn't be such a problem, the old ones, I wouldn't be comfortable running them close to their rated voltage unless they had been run there all the time.

author: ez24
author_rank: Super Contributor
timestamp: September 30, 2015, 04:21:47 am
content: Quote from: Alex Eisenhut on September 29, 2015, 11:38:34 pmThought you ended up at Batteriser - they may need you

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: September 30, 2015, 11:51:41 pm
content: Quote from: ez24 on September 30, 2015, 04:21:47 amLOL I only do buck converters

author: AF6LJ
author_rank: Unknown
timestamp: October 01, 2015, 12:03:15 am
content: Quote from: Alex Eisenhut on September 30, 2015, 11:51:41 pmThose are very cool; if you should decide to sell them please let us know.