TO-39 heat sink - Page 1
Forum section: electronics / projects

author: Cicada
author_rank: Regular Contributor
timestamp: July 11, 2022, 01:29:50 pm
content: HiI need to reproduce the card in the attached picture. Its is a card from the 80's i.e. out of a Systron Donner M107 power supply.The TO-39 packages have small heat sinks on with the characters THM 1115 stamped on it.I have google searched for TO-39 heat sinks with no success to find the exact heat sinks used on the card.I have some of the heat sinks in the attached picture. They cover a bigger area on the board around the transistor. I guess I can spread out the components to not make all devices fit. But I was wondering if anyone can point me to a source of these heat sinks used on the original card.Thanks

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 11, 2022, 02:12:25 pm
content: Reproduce part-for-part? Those are... hmm, surprisingly still available come to think of it, well, not so much the BU205.Why not 2N3439 --> PBHV8540X,115 or DI2579N, and BU205 --> FJPF5027RTU or so? SMTs can be heatsinked with copper pours (add thermal interface material and heatsinking if needed), TO-220 can be heatsinked in the same space as the TO-3 with far less bother.What is that doing, anyway? The 2N3439s just look to be in a divider chain of some sort.Tim

author: Cicada
author_rank: Regular Contributor
timestamp: July 11, 2022, 02:30:13 pm
content: Quote from: T3sl4co1l on July 11, 2022, 02:12:25 pmhttps://www.mouser.co.za/ProductDetail/Central-Semiconductor/2N3439-PBFREE?qs=u16ybLDytRZk0NEL8JQPBQ%3D%3DQuote from: T3sl4co1l on July 11, 2022, 02:12:25 pmWas difficult to source BU205 but I did get stock. BU205 is expensive so I opted for NTE165. Search for BU205 here and they state the equivalent is NTE165https://www.nteinc.com/search.phpI compared the datasheets and they are pretty much a match.Quote from: T3sl4co1l on July 11, 2022, 02:12:25 pmThus far I have not really considered anything else than copy and paste i.e. try to implement the original design as is.Quote from: T3sl4co1l on July 11, 2022, 02:12:25 pmSee the attached schematic and documents of the A6 high voltage amplifier card used in the Systron Donner Prescision DC voltage source.The service manual for the M107 can be found here.https://elektrotanya.com/systron_donner_m107_precision_dc_voltage_source.pdf/download.htmlUSER "Intabits" have a nice series about his work on one of these units.https://www.eevblog.com/forum/testgear/systron-donner-m107-precision-dc-voltage-source-teardown-video/msg3566730/#msg3566730

author: Cicada
author_rank: Regular Contributor
timestamp: July 11, 2022, 02:32:21 pm
content: USER "Intabits" have a nice series about his work on one of these units.https://www.eevblog.com/forum/testgear/systron-donner-m107-precision-dc-voltage-source-teardown-video/msg3566730/#msg3566730

author: coromonadalix
author_rank: Super Contributor
timestamp: July 11, 2022, 02:34:34 pm
content: to-99 and to-39 heatsinks are not hard to find ??since you're duplicating the board you can / could move them to add more heatsink ''mass around / on them''they must be used in some voltage divider page 118 ... never saw that designhttps://elektrotanya.com/systron_donner_m107_precision_dc_voltage_source.pdf/download.html#dlEDIT OOPS TO LATE LOLL

author: Benta
author_rank: Super Contributor
timestamp: July 11, 2022, 04:56:36 pm
content: The extruded heat sinks you'll get from multiple sources. Example:https://www.amazon.com/Aluminum-Sinks-OPA627SM-LME49720HA-OPA128KM/dp/B07NYB113Q

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 11, 2022, 06:27:33 pm
content: Oh yeah even better, those could be replaced by--like, the whole freaking thing--a couple of MOSFETs, and a few BJTs at the bottom to do whatever is going on here, still need to match to the same control interface after all. Those 2N3439 chains are only needed because BU205's hFE is nil; a straight resistor divider into MOSFET gate will do (don't forget a source to gate zener, just in case).It's drawn terribly (as was sadly so often the case, back in the day.....or still today...) but I think it's just a common-emitter cascode (Q12 common to -15V, Q3 on top of it with 68k+220k divider into its base), so Q3 collector is the gain node, and Q2 is the follower, with extra help from Q1 and the divider-follower chain. Q3 doesn't need a further cascode, I think because it's running at low enough current (1.5mA) and in such a configuration that they must not need to worry about Vceo (a mere 700V) but can harness the full Vcbo (1500V) range; meanwhile Q1-Q2 can't, because they have to deliver full load current, whatever that is (all of 2.6mA?).There's also Q4, which I guess bleeds in more current when set below 140V; does the supply have a higher output rating at low voltage? Up to 40mA or so, I guess?Neat thing with MOSFETs is, with heatsinks filling the same space as the existing board, you could probably up the capacity to... well, hell, 30, 50, 100mA even, assuming the +1500V supply can deliver it; among many other considerations, naturally. The board can be very low profile with SMTs and a few THTs, and the rest of the space can be heat dissipation. You'd also want to add a current limit here, I think; this may well be hFE-limited, which is... gnarly to say the least, and utterly inapplicable with MOSFETs in play. But that's easy, a little current sense transistor (like Q4, but pulling down on the gain node, not sucking in additional power!) will do. And more accurately than whatever this circuit had, in and of itself at least. (I'm guessing the two inputs were for voltage and current control or something like that, but through a more roundabout means, not all right here.)It could also be faster, or higher voltage, or.... well, I digress. Needless to say, semiconductor technology has vastly improved on the bad old days.Tim

author: andy3055
author_rank: Super Contributor
timestamp: July 16, 2022, 07:30:52 pm
content: You mean this?

author: Gyro
author_rank: Super Contributor
timestamp: July 16, 2022, 07:40:31 pm
content: Quote from: andy3055 on July 16, 2022, 07:30:52 pmNo, that's a TO3 heatsink. The OP is referring to the TO39 transistors around it. The heatsink in the OP's second image are around 50'C/W iirc. The metal sleeves on the existing board barely look like heatsinks at all, I would think they are 100'C/W at least.

author: andy3055
author_rank: Super Contributor
timestamp: July 16, 2022, 07:59:10 pm
content: You are correct. Those small heat sinks don't seem to be the prominent in that photo and I thought he made a mistake!OP: You can get some aluminum tubing and make them by slitting them.

author: nigelwright7557
author_rank: Frequent Contributor
timestamp: July 16, 2022, 09:36:30 pm
content: Loads on ebay.The last time I used them was 1980 on a Maplin power amplifier which I have still got.

author: David Hess
author_rank: Super Contributor
timestamp: July 16, 2022, 10:01:21 pm
content: If I wanted to keep the original design, I would likely replace the TO-39 parts with modern TO-225 or TO-220 parts which will be much easier to find heat sinks for, but TO-39 heat sinks should not be difficult to find. Aluminum tabs could be epoxied onto the tops.Quote from: T3sl4co1l on July 11, 2022, 06:27:33 pmI thought it was foldback current limiting, but instead it unloads the high voltage pass element below 140 volts and supplies extra output current, and then drive to the high voltage pass element is cut through R15 and R16 if the output voltage falls lower?

author: David Hess
author_rank: Super Contributor
timestamp: July 16, 2022, 10:03:59 pm
content: Quote from: Gyro on July 16, 2022, 07:40:31 pmI would not underestimate them. Small "medium power" packages are good for a watt or two, so adding even an insignificant heat sink like that can boost the power to 5 watts or so.