Author Topic: My TO-3 switcher (buck converter)  (Read 25573 times)

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Offline Alex Eisenhut

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My TO-3 switcher (buck converter)
« on: July 17, 2015, 02:22:31 am »
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/3516739

Whacking 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.
 

Offline fivefish

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Re: My TO-3 switcher (buck converter)
« Reply #1 on: July 17, 2015, 03:54:06 am »
This is awesome... following.
 

Offline Paul Moir

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Re: My TO-3 switcher (buck converter)
« Reply #2 on: July 17, 2015, 05:13:47 am »
::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...

« Last Edit: July 17, 2015, 05:29:33 am by Paul Moir »
 

Offline T3sl4co1l

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Re: My TO-3 switcher (buck converter)
« Reply #3 on: July 17, 2015, 05:45:22 am »
Sexy :)

Did you manage to get the filtering you wanted, in the end?
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Offline SeanB

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Re: My TO-3 switcher (buck converter)
« Reply #4 on: July 18, 2015, 10:35:22 am »
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.
 

Offline LukeW

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Re: My TO-3 switcher (buck converter)
« Reply #5 on: July 18, 2015, 10:44:44 am »
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.
 

Offline codeboy2k

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Re: My TO-3 switcher (buck converter)
« Reply #6 on: July 18, 2015, 03:12:33 pm »
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. 
 

Offline fcb

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Re: My TO-3 switcher (buck converter)
« Reply #7 on: July 18, 2015, 03:23:49 pm »
Very nice work Alex and a great idea.

 

Offline zapta

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Re: My TO-3 switcher (buck converter)
« Reply #8 on: July 18, 2015, 05:12:49 pm »
Looks very nice. You can 3D print a matching cover.
Drain the swamp.
 

Offline calexanian

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Re: My TO-3 switcher (buck converter)
« Reply #9 on: July 18, 2015, 05:58:17 pm »
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.
Charles Alexanian
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Offline calexanian

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Re: My TO-3 switcher (buck converter)
« Reply #10 on: July 18, 2015, 06:04:20 pm »
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.
Charles Alexanian
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Offline blueskull

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Re: My TO-3 switcher (buck converter)
« Reply #11 on: July 18, 2015, 09:17:19 pm »
Sexy work. Looks beautiful.

I recommend SnPb solder if you can obtain. If not, try to dissolve some gold or scrape away some gold before using SAC solder.

At high temp, IMC of gold is quite nasty. I recommend nickel/palladium plated pins instead of gold plated pins.
 

Offline Alex Eisenhut

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Re: My TO-3 switcher (buck converter)
« Reply #12 on: July 19, 2015, 05:10:34 pm »
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...
 

Offline SeanB

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Re: My TO-3 switcher (buck converter)
« Reply #13 on: July 19, 2015, 05:21:10 pm »
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.
 

Offline marshallh

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Re: My TO-3 switcher (buck converter)
« Reply #14 on: July 19, 2015, 05:24:12 pm »
Oshpark doesn't have any rules about coppter to pcb outline. In fact you can make the mill cut through the copper (not recommended).
Verilog tips
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Online MagicSmoker

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Re: My TO-3 switcher (buck converter)
« Reply #15 on: July 19, 2015, 09:38:31 pm »
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.
 

Offline Alex Eisenhut

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Re: My TO-3 switcher (buck converter)
« Reply #16 on: July 24, 2015, 03:21:32 am »
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.

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.

I 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.  >:(

Looks very nice. You can 3D print a matching cover.

The thought occurred. I want to make a clip-on doodad with a Commodore logo on it. Maybe.

Sexy :)

Did you manage to get the filtering you wanted, in the end?

A quick look with the scope shows about 60mV of noise on the output. Good enough for TTL work...
 

Offline Mr.B

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Re: My TO-3 switcher (buck converter)
« Reply #17 on: July 24, 2015, 03:38:05 am »
Very impressive.
Well done!
Time is the overseer of all things.
 

Offline LukeW

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Re: My TO-3 switcher (buck converter)
« Reply #18 on: July 24, 2015, 08:31:47 am »
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.
 

Offline SeanB

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Re: My TO-3 switcher (buck converter)
« Reply #19 on: July 25, 2015, 09:24:13 am »
A quick look with the scope shows about 60mV of noise on the output. Good enough for TTL work...

I 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.
 

Offline Alex Eisenhut

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Re: My TO-3 switcher (buck converter)
« Reply #20 on: July 25, 2015, 01:05:47 pm »
A quick look with the scope shows about 60mV of noise on the output. Good enough for TTL work...

I 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.

Then 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...
 

Offline SeanB

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Re: My TO-3 switcher (buck converter)
« Reply #21 on: July 25, 2015, 01:50:09 pm »
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.
 

Offline Alex Eisenhut

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Re: My TO-3 switcher (buck converter)
« Reply #22 on: July 25, 2015, 03:54:10 pm »
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.

:) I 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.  :-DD

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.
 

Offline Tachyon

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Re: My TO-3 switcher (buck converter)
« Reply #23 on: July 26, 2015, 05:07:40 am »
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.
 

Offline SeanB

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Re: My TO-3 switcher (buck converter)
« Reply #24 on: July 26, 2015, 07:45:18 am »
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.
 


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