On Wed, 23 Jun 2021 08:51:05 -0700, jlarkin@highlandsniptechnology.com wrote:>On Tue, 22 Jun 2021 23:40:12 -0700, boB <boB@K7IQ.com> wrote: > >>On Tue, 22 Jun 2021 21:55:59 -0700, boB <boB@K7IQ.com> wrote: >> >>>On Tue, 22 Jun 2021 07:08:10 -0700, jlarkin@highlandsniptechnology.com >>>wrote: >>> >>>>On Mon, 21 Jun 2021 21:25:38 -0700, boB <boB@K7IQ.com> wrote: >>>> >>>>>On Mon, 21 Jun 2021 15:15:30 -0700, John Larkin >>>>><jjlarkin@highlandtechnology.com> wrote: >>>>> >>>>>>On Mon, 21 Jun 2021 16:50:04 -0400, legg <legg@nospam.magma.ca> wrote: >>>>>> >>>>>>>On Mon, 21 Jun 2021 11:00:18 -0700, John Larkin >>>>>>><jjlarkin@highlandtechnology.com> wrote: >>>>>>> >>>>>>>>On Mon, 21 Jun 2021 19:44:55 +0200, Piotr Wyderski >>>>>>>><bombald@protonmail.com> wrote: >>>>>>>> >>>>>>>>>John Larkin wrote: >>>>>>>>> >>>>>>>>>> I'm not having much luck searching for isolated-tab mosfets. Ideal >>>>>>>>>> would be a dpak n-channel. Any suggestions? >>>>>>>>> >>>>>>>>>Are there any SMD parts with isolated tab? That would be interesting. >>>>>>>>>OTOH, a ceramic tab made of AlN shouldn't be that expensive and the >>>>>>>>>thermal parameters would be great. >>>>>>>>> >>>>>>>>> Best regards, Piotr >>>>>>>> >>>>>>>>There are TO-220s with isolated tabs. >>>>>>>> >>>>>>>>I'll be using two n-fets per channel, in a multichannel programmable >>>>>>>>load board. If they were isolated, a pair of fets could share heat >>>>>>>>sinking. >>>>>>>> >>>>>>>>Isolated DPAKs with the solder-on straddling heat sinks would be >>>>>>>>ideal, all surface mount. >>>>>>> >>>>>>>Isolated surface-mount parts that share a heatsink. >>>>>>> >>>>>>>Surface mount heat sink - it does not compute. >>>>>>> >>>>>>>RL >>>>>> >>>>>>There are tons of heat sinks in this style: >>>>>> >>>>>>https://www.digikey.com/en/products/detail/aavid-thermal-division-of-boyd-corporation/573400D00000G/1625551 >>>>>> >>>>>>https://www.digikey.com/en/products/detail/wakefield-vette/217-36CTE6/1033769 >>>>>> >>>>>>They straddle a DPAK on the board. One pass through the reflow oven >>>>>>can solder the fet and the heat sink. >>>>>> >>>>>>My programmable load circuit sinks AC or DC. It uses two mosfets. If >>>>>>the source is AC, they share the dissipation. If DC, only one gets >>>>>>hot. So it would be great to share the heat sinking. >>>>>> >>>>>>Using two non-isolated fets and two heat sinks, the trick would be to >>>>>>transfer heat between the two but keep them insulated. That could >>>>>>work. >>>>> >>>>> >>>>>There are lots of isolated tab D-Squared paks (TO-263 ?) Most we >>>>>use will have a TO-220 and D-Squared package with the same die. >>>>> >>>>>We also use D-Pak N channel FETs and P channel D-Pak FETs. >>>>> >>>>>Look at IRF part numbers for D-Pak as I remember that we use. >>>> >>>>I can't find any isolated dpak fets. Got any part numbers? >>>> >>>>There are isolated TO-220s, mostly obsolete. But if I use TO-220s, I >>>>can bolt them to a big heat sink with insulators. Last resort. >>>> >>>>Some PCB layout tricks might couple them thermally but provide >>>>insulation. Not perfect, but better than nothing. >>>> >>>>> >>>>>And you can heat sink D2Pak FETs. Just have to think about it. >>>>>We do kilo-watts with D-Squared isolated. 7 lead and 3 lead with the >>>>>middle lead missing of course. >>>> >>>>Got part numbers? >>> >>>Uh OH ! My brain COMPLETELY farted ! >>> >>>Either that or I was drunk. But I don't even drink ! >>> >>>For some reason I got isolated and non-isolated reversed ! >>> >>>Ooops. Sorry. >>> >>>I have used isolated TO-220s before but I don't think I have seen an >>>isolated DPAK either. >>> >>> >> >>Thinking about this again... If a D-Pak has the middle drain pin >>cut, same as a typical TO-263 D2PAK, how would you access the drain >>except by the tab ? >> > >It would need a middle pin. > >There are some isolated-tab power opamps around, so it's not >impossible. But I'd better work with standard parts to be safe.Yeah, I've only seen TO-220's with the isolated tab. IN general, the thermal resistance may or may not be up to par for your requirements. We see FET representatives all the time and will ask next time I see them. Now you have my curiousity up.
isolated mosfets
Started by ●June 21, 2021
Reply by ●June 23, 20212021-06-23
Reply by ●June 24, 20212021-06-24
On Wed, 23 Jun 2021 11:08:54 -0700, boB <boB@K7IQ.com> wrote:>On Wed, 23 Jun 2021 08:51:05 -0700, jlarkin@highlandsniptechnology.com >wrote: > >>On Tue, 22 Jun 2021 23:40:12 -0700, boB <boB@K7IQ.com> wrote: >> >>>On Tue, 22 Jun 2021 21:55:59 -0700, boB <boB@K7IQ.com> wrote: >>> >>>>On Tue, 22 Jun 2021 07:08:10 -0700, jlarkin@highlandsniptechnology.com >>>>wrote: >>>> >>>>>On Mon, 21 Jun 2021 21:25:38 -0700, boB <boB@K7IQ.com> wrote: >>>>> >>>>>>On Mon, 21 Jun 2021 15:15:30 -0700, John Larkin >>>>>><jjlarkin@highlandtechnology.com> wrote: >>>>>> >>>>>>>On Mon, 21 Jun 2021 16:50:04 -0400, legg <legg@nospam.magma.ca> wrote: >>>>>>> >>>>>>>>On Mon, 21 Jun 2021 11:00:18 -0700, John Larkin >>>>>>>><jjlarkin@highlandtechnology.com> wrote: >>>>>>>> >>>>>>>>>On Mon, 21 Jun 2021 19:44:55 +0200, Piotr Wyderski >>>>>>>>><bombald@protonmail.com> wrote: >>>>>>>>> >>>>>>>>>>John Larkin wrote: >>>>>>>>>> >>>>>>>>>>> I'm not having much luck searching for isolated-tab mosfets. Ideal >>>>>>>>>>> would be a dpak n-channel. Any suggestions? >>>>>>>>>> >>>>>>>>>>Are there any SMD parts with isolated tab? That would be interesting. >>>>>>>>>>OTOH, a ceramic tab made of AlN shouldn't be that expensive and the >>>>>>>>>>thermal parameters would be great. >>>>>>>>>> >>>>>>>>>> Best regards, Piotr >>>>>>>>> >>>>>>>>>There are TO-220s with isolated tabs. >>>>>>>>> >>>>>>>>>I'll be using two n-fets per channel, in a multichannel programmable >>>>>>>>>load board. If they were isolated, a pair of fets could share heat >>>>>>>>>sinking. >>>>>>>>> >>>>>>>>>Isolated DPAKs with the solder-on straddling heat sinks would be >>>>>>>>>ideal, all surface mount. >>>>>>>> >>>>>>>>Isolated surface-mount parts that share a heatsink. >>>>>>>> >>>>>>>>Surface mount heat sink - it does not compute. >>>>>>>> >>>>>>>>RL >>>>>>> >>>>>>>There are tons of heat sinks in this style: >>>>>>> >>>>>>>https://www.digikey.com/en/products/detail/aavid-thermal-division-of-boyd-corporation/573400D00000G/1625551 >>>>>>> >>>>>>>https://www.digikey.com/en/products/detail/wakefield-vette/217-36CTE6/1033769 >>>>>>> >>>>>>>They straddle a DPAK on the board. One pass through the reflow oven >>>>>>>can solder the fet and the heat sink. >>>>>>> >>>>>>>My programmable load circuit sinks AC or DC. It uses two mosfets. If >>>>>>>the source is AC, they share the dissipation. If DC, only one gets >>>>>>>hot. So it would be great to share the heat sinking. >>>>>>> >>>>>>>Using two non-isolated fets and two heat sinks, the trick would be to >>>>>>>transfer heat between the two but keep them insulated. That could >>>>>>>work. >>>>>> >>>>>> >>>>>>There are lots of isolated tab D-Squared paks (TO-263 ?) Most we >>>>>>use will have a TO-220 and D-Squared package with the same die. >>>>>> >>>>>>We also use D-Pak N channel FETs and P channel D-Pak FETs. >>>>>> >>>>>>Look at IRF part numbers for D-Pak as I remember that we use. >>>>> >>>>>I can't find any isolated dpak fets. Got any part numbers? >>>>> >>>>>There are isolated TO-220s, mostly obsolete. But if I use TO-220s, I >>>>>can bolt them to a big heat sink with insulators. Last resort. >>>>> >>>>>Some PCB layout tricks might couple them thermally but provide >>>>>insulation. Not perfect, but better than nothing. >>>>> >>>>>> >>>>>>And you can heat sink D2Pak FETs. Just have to think about it. >>>>>>We do kilo-watts with D-Squared isolated. 7 lead and 3 lead with the >>>>>>middle lead missing of course. >>>>> >>>>>Got part numbers? >>>> >>>>Uh OH ! My brain COMPLETELY farted ! >>>> >>>>Either that or I was drunk. But I don't even drink ! >>>> >>>>For some reason I got isolated and non-isolated reversed ! >>>> >>>>Ooops. Sorry. >>>> >>>>I have used isolated TO-220s before but I don't think I have seen an >>>>isolated DPAK either. >>>> >>>> >>> >>>Thinking about this again... If a D-Pak has the middle drain pin >>>cut, same as a typical TO-263 D2PAK, how would you access the drain >>>except by the tab ? >>> >> >>It would need a middle pin. >> >>There are some isolated-tab power opamps around, so it's not >>impossible. But I'd better work with standard parts to be safe. > >Yeah, I've only seen TO-220's with the isolated tab. > >IN general, the thermal resistance may or may not be up to par for >your requirements. > >We see FET representatives all the time and will ask next time I see >them. Now you have my curiousity up. > > >Lasse reminded me about AlN thermal jumpers, which really helps the heat sharing situation between the two dpak heat sinks. https://www.dropbox.com/s/l4vums9qosarov4/Dpak_Heat_Sink_2.jpg?raw=1 With 8 programmable load circuits on a board, and some air flow, I'm thinking 10 watts per channel should be OK. -- John Larkin Highland Technology, Inc The best designs are necessarily accidental.
Reply by ●June 24, 20212021-06-24
torsdag den 24. juni 2021 kl. 05.46.56 UTC+2 skrev jla...@highlandsniptechnology.com:> On Wed, 23 Jun 2021 11:08:54 -0700, boB <b...@K7IQ.com> wrote: > > >On Wed, 23 Jun 2021 08:51:05 -0700, jla...@highlandsniptechnology.com > >wrote: > > > >>On Tue, 22 Jun 2021 23:40:12 -0700, boB <b...@K7IQ.com> wrote: > >> > >>>On Tue, 22 Jun 2021 21:55:59 -0700, boB <b...@K7IQ.com> wrote: > >>> > >>>>On Tue, 22 Jun 2021 07:08:10 -0700, jla...@highlandsniptechnology.com > >>>>wrote: > >>>> > >>>>>On Mon, 21 Jun 2021 21:25:38 -0700, boB <b...@K7IQ.com> wrote: > >>>>> > >>>>>>On Mon, 21 Jun 2021 15:15:30 -0700, John Larkin > >>>>>><jjla...@highlandtechnology.com> wrote: > >>>>>> > >>>>>>>On Mon, 21 Jun 2021 16:50:04 -0400, legg <le...@nospam.magma.ca> wrote: > >>>>>>> > >>>>>>>>On Mon, 21 Jun 2021 11:00:18 -0700, John Larkin > >>>>>>>><jjla...@highlandtechnology.com> wrote: > >>>>>>>> > >>>>>>>>>On Mon, 21 Jun 2021 19:44:55 +0200, Piotr Wyderski > >>>>>>>>><bom...@protonmail.com> wrote: > >>>>>>>>> > >>>>>>>>>>John Larkin wrote: > >>>>>>>>>> > >>>>>>>>>>> I'm not having much luck searching for isolated-tab mosfets. Ideal > >>>>>>>>>>> would be a dpak n-channel. Any suggestions? > >>>>>>>>>> > >>>>>>>>>>Are there any SMD parts with isolated tab? That would be interesting. > >>>>>>>>>>OTOH, a ceramic tab made of AlN shouldn't be that expensive and the > >>>>>>>>>>thermal parameters would be great. > >>>>>>>>>> > >>>>>>>>>> Best regards, Piotr > >>>>>>>>> > >>>>>>>>>There are TO-220s with isolated tabs. > >>>>>>>>> > >>>>>>>>>I'll be using two n-fets per channel, in a multichannel programmable > >>>>>>>>>load board. If they were isolated, a pair of fets could share heat > >>>>>>>>>sinking. > >>>>>>>>> > >>>>>>>>>Isolated DPAKs with the solder-on straddling heat sinks would be > >>>>>>>>>ideal, all surface mount. > >>>>>>>> > >>>>>>>>Isolated surface-mount parts that share a heatsink. > >>>>>>>> > >>>>>>>>Surface mount heat sink - it does not compute. > >>>>>>>> > >>>>>>>>RL > >>>>>>> > >>>>>>>There are tons of heat sinks in this style: > >>>>>>> > >>>>>>>https://www.digikey.com/en/products/detail/aavid-thermal-division-of-boyd-corporation/573400D00000G/1625551 > >>>>>>> > >>>>>>>https://www.digikey.com/en/products/detail/wakefield-vette/217-36CTE6/1033769 > >>>>>>> > >>>>>>>They straddle a DPAK on the board. One pass through the reflow oven > >>>>>>>can solder the fet and the heat sink. > >>>>>>> > >>>>>>>My programmable load circuit sinks AC or DC. It uses two mosfets. If > >>>>>>>the source is AC, they share the dissipation. If DC, only one gets > >>>>>>>hot. So it would be great to share the heat sinking. > >>>>>>> > >>>>>>>Using two non-isolated fets and two heat sinks, the trick would be to > >>>>>>>transfer heat between the two but keep them insulated. That could > >>>>>>>work. > >>>>>> > >>>>>> > >>>>>>There are lots of isolated tab D-Squared paks (TO-263 ?) Most we > >>>>>>use will have a TO-220 and D-Squared package with the same die. > >>>>>> > >>>>>>We also use D-Pak N channel FETs and P channel D-Pak FETs. > >>>>>> > >>>>>>Look at IRF part numbers for D-Pak as I remember that we use. > >>>>> > >>>>>I can't find any isolated dpak fets. Got any part numbers? > >>>>> > >>>>>There are isolated TO-220s, mostly obsolete. But if I use TO-220s, I > >>>>>can bolt them to a big heat sink with insulators. Last resort. > >>>>> > >>>>>Some PCB layout tricks might couple them thermally but provide > >>>>>insulation. Not perfect, but better than nothing. > >>>>> > >>>>>> > >>>>>>And you can heat sink D2Pak FETs. Just have to think about it. > >>>>>>We do kilo-watts with D-Squared isolated. 7 lead and 3 lead with the > >>>>>>middle lead missing of course. > >>>>> > >>>>>Got part numbers? > >>>> > >>>>Uh OH ! My brain COMPLETELY farted ! > >>>> > >>>>Either that or I was drunk. But I don't even drink ! > >>>> > >>>>For some reason I got isolated and non-isolated reversed ! > >>>> > >>>>Ooops. Sorry. > >>>> > >>>>I have used isolated TO-220s before but I don't think I have seen an > >>>>isolated DPAK either. > >>>> > >>>> > >>> > >>>Thinking about this again... If a D-Pak has the middle drain pin > >>>cut, same as a typical TO-263 D2PAK, how would you access the drain > >>>except by the tab ? > >>> > >> > >>It would need a middle pin. > >> > >>There are some isolated-tab power opamps around, so it's not > >>impossible. But I'd better work with standard parts to be safe. > > > >Yeah, I've only seen TO-220's with the isolated tab. > > > >IN general, the thermal resistance may or may not be up to par for > >your requirements. > > > >We see FET representatives all the time and will ask next time I see > >them. Now you have my curiousity up. > > > > > > > Lasse reminded me about AlN thermal jumpers, which really helps the > heat sharing situation between the two dpak heat sinks. > > https://www.dropbox.com/s/l4vums9qosarov4/Dpak_Heat_Sink_2.jpg?raw=1 > > > With 8 programmable load circuits on a board, and some air flow, I'm > thinking 10 watts per channel should be OK.include some through hole pads in the footprint for an easy upgrade with TO220/TO247
Reply by ●June 24, 20212021-06-24
On Thu, 24 Jun 2021 09:19:47 -0700 (PDT), Lasse Langwadt Christensen <langwadt@fonz.dk> wrote:>torsdag den 24. juni 2021 kl. 05.46.56 UTC+2 skrev jla...@highlandsniptechnology.com: >> On Wed, 23 Jun 2021 11:08:54 -0700, boB <b...@K7IQ.com> wrote: >> >> >On Wed, 23 Jun 2021 08:51:05 -0700, jla...@highlandsniptechnology.com >> >wrote: >> > >> >>On Tue, 22 Jun 2021 23:40:12 -0700, boB <b...@K7IQ.com> wrote: >> >> >> >>>On Tue, 22 Jun 2021 21:55:59 -0700, boB <b...@K7IQ.com> wrote: >> >>> >> >>>>On Tue, 22 Jun 2021 07:08:10 -0700, jla...@highlandsniptechnology.com >> >>>>wrote: >> >>>> >> >>>>>On Mon, 21 Jun 2021 21:25:38 -0700, boB <b...@K7IQ.com> wrote: >> >>>>> >> >>>>>>On Mon, 21 Jun 2021 15:15:30 -0700, John Larkin >> >>>>>><jjla...@highlandtechnology.com> wrote: >> >>>>>> >> >>>>>>>On Mon, 21 Jun 2021 16:50:04 -0400, legg <le...@nospam.magma.ca> wrote: >> >>>>>>> >> >>>>>>>>On Mon, 21 Jun 2021 11:00:18 -0700, John Larkin >> >>>>>>>><jjla...@highlandtechnology.com> wrote: >> >>>>>>>> >> >>>>>>>>>On Mon, 21 Jun 2021 19:44:55 +0200, Piotr Wyderski >> >>>>>>>>><bom...@protonmail.com> wrote: >> >>>>>>>>> >> >>>>>>>>>>John Larkin wrote: >> >>>>>>>>>> >> >>>>>>>>>>> I'm not having much luck searching for isolated-tab mosfets. Ideal >> >>>>>>>>>>> would be a dpak n-channel. Any suggestions? >> >>>>>>>>>> >> >>>>>>>>>>Are there any SMD parts with isolated tab? That would be interesting. >> >>>>>>>>>>OTOH, a ceramic tab made of AlN shouldn't be that expensive and the >> >>>>>>>>>>thermal parameters would be great. >> >>>>>>>>>> >> >>>>>>>>>> Best regards, Piotr >> >>>>>>>>> >> >>>>>>>>>There are TO-220s with isolated tabs. >> >>>>>>>>> >> >>>>>>>>>I'll be using two n-fets per channel, in a multichannel programmable >> >>>>>>>>>load board. If they were isolated, a pair of fets could share heat >> >>>>>>>>>sinking. >> >>>>>>>>> >> >>>>>>>>>Isolated DPAKs with the solder-on straddling heat sinks would be >> >>>>>>>>>ideal, all surface mount. >> >>>>>>>> >> >>>>>>>>Isolated surface-mount parts that share a heatsink. >> >>>>>>>> >> >>>>>>>>Surface mount heat sink - it does not compute. >> >>>>>>>> >> >>>>>>>>RL >> >>>>>>> >> >>>>>>>There are tons of heat sinks in this style: >> >>>>>>> >> >>>>>>>https://www.digikey.com/en/products/detail/aavid-thermal-division-of-boyd-corporation/573400D00000G/1625551 >> >>>>>>> >> >>>>>>>https://www.digikey.com/en/products/detail/wakefield-vette/217-36CTE6/1033769 >> >>>>>>> >> >>>>>>>They straddle a DPAK on the board. One pass through the reflow oven >> >>>>>>>can solder the fet and the heat sink. >> >>>>>>> >> >>>>>>>My programmable load circuit sinks AC or DC. It uses two mosfets. If >> >>>>>>>the source is AC, they share the dissipation. If DC, only one gets >> >>>>>>>hot. So it would be great to share the heat sinking. >> >>>>>>> >> >>>>>>>Using two non-isolated fets and two heat sinks, the trick would be to >> >>>>>>>transfer heat between the two but keep them insulated. That could >> >>>>>>>work. >> >>>>>> >> >>>>>> >> >>>>>>There are lots of isolated tab D-Squared paks (TO-263 ?) Most we >> >>>>>>use will have a TO-220 and D-Squared package with the same die. >> >>>>>> >> >>>>>>We also use D-Pak N channel FETs and P channel D-Pak FETs. >> >>>>>> >> >>>>>>Look at IRF part numbers for D-Pak as I remember that we use. >> >>>>> >> >>>>>I can't find any isolated dpak fets. Got any part numbers? >> >>>>> >> >>>>>There are isolated TO-220s, mostly obsolete. But if I use TO-220s, I >> >>>>>can bolt them to a big heat sink with insulators. Last resort. >> >>>>> >> >>>>>Some PCB layout tricks might couple them thermally but provide >> >>>>>insulation. Not perfect, but better than nothing. >> >>>>> >> >>>>>> >> >>>>>>And you can heat sink D2Pak FETs. Just have to think about it. >> >>>>>>We do kilo-watts with D-Squared isolated. 7 lead and 3 lead with the >> >>>>>>middle lead missing of course. >> >>>>> >> >>>>>Got part numbers? >> >>>> >> >>>>Uh OH ! My brain COMPLETELY farted ! >> >>>> >> >>>>Either that or I was drunk. But I don't even drink ! >> >>>> >> >>>>For some reason I got isolated and non-isolated reversed ! >> >>>> >> >>>>Ooops. Sorry. >> >>>> >> >>>>I have used isolated TO-220s before but I don't think I have seen an >> >>>>isolated DPAK either. >> >>>> >> >>>> >> >>> >> >>>Thinking about this again... If a D-Pak has the middle drain pin >> >>>cut, same as a typical TO-263 D2PAK, how would you access the drain >> >>>except by the tab ? >> >>> >> >> >> >>It would need a middle pin. >> >> >> >>There are some isolated-tab power opamps around, so it's not >> >>impossible. But I'd better work with standard parts to be safe. >> > >> >Yeah, I've only seen TO-220's with the isolated tab. >> > >> >IN general, the thermal resistance may or may not be up to par for >> >your requirements. >> > >> >We see FET representatives all the time and will ask next time I see >> >them. Now you have my curiousity up. >> > >> > >> > >> Lasse reminded me about AlN thermal jumpers, which really helps the >> heat sharing situation between the two dpak heat sinks. >> >> https://www.dropbox.com/s/l4vums9qosarov4/Dpak_Heat_Sink_2.jpg?raw=1 >> >> >> With 8 programmable load circuits on a board, and some air flow, I'm >> thinking 10 watts per channel should be OK. > >include some through hole pads in the footprint for an easy upgrade with TO220/TO247 > >There are d and d2 pak fets rated for hundreds of watts; my limit is heat sinking. I think I want to get the tabs of the fets as close as possible and squeeze 2 or 3 of the AlN thermal bridges between them. If I go with 1 oz copper on layer 1, that's 70K/W per square, so I need to minimize that spreading thermal resistance. The tabs are nice chunks of copper. How hot should I let the fets get? 80C? -- John Larkin Highland Technology, Inc The best designs are necessarily accidental.
Reply by ●June 24, 20212021-06-24
torsdag den 24. juni 2021 kl. 18.40.20 UTC+2 skrev jla...@highlandsniptechnology.com:> On Thu, 24 Jun 2021 09:19:47 -0700 (PDT), Lasse Langwadt Christensen > <lang...@fonz.dk> wrote: > > >torsdag den 24. juni 2021 kl. 05.46.56 UTC+2 skrev jla...@highlandsniptechnology.com: > >> On Wed, 23 Jun 2021 11:08:54 -0700, boB <b...@K7IQ.com> wrote: > >> > >> >On Wed, 23 Jun 2021 08:51:05 -0700, jla...@highlandsniptechnology.com > >> >wrote: > >> > > >> >>On Tue, 22 Jun 2021 23:40:12 -0700, boB <b...@K7IQ.com> wrote: > >> >> > >> >>>On Tue, 22 Jun 2021 21:55:59 -0700, boB <b...@K7IQ.com> wrote: > >> >>> > >> >>>>On Tue, 22 Jun 2021 07:08:10 -0700, jla...@highlandsniptechnology.com > >> >>>>wrote: > >> >>>> > >> >>>>>On Mon, 21 Jun 2021 21:25:38 -0700, boB <b...@K7IQ.com> wrote: > >> >>>>> > >> >>>>>>On Mon, 21 Jun 2021 15:15:30 -0700, John Larkin > >> >>>>>><jjla...@highlandtechnology.com> wrote: > >> >>>>>> > >> >>>>>>>On Mon, 21 Jun 2021 16:50:04 -0400, legg <le...@nospam.magma.ca> wrote: > >> >>>>>>> > >> >>>>>>>>On Mon, 21 Jun 2021 11:00:18 -0700, John Larkin > >> >>>>>>>><jjla...@highlandtechnology.com> wrote: > >> >>>>>>>> > >> >>>>>>>>>On Mon, 21 Jun 2021 19:44:55 +0200, Piotr Wyderski > >> >>>>>>>>><bom...@protonmail.com> wrote: > >> >>>>>>>>> > >> >>>>>>>>>>John Larkin wrote: > >> >>>>>>>>>> > >> >>>>>>>>>>> I'm not having much luck searching for isolated-tab mosfets. Ideal > >> >>>>>>>>>>> would be a dpak n-channel. Any suggestions? > >> >>>>>>>>>> > >> >>>>>>>>>>Are there any SMD parts with isolated tab? That would be interesting. > >> >>>>>>>>>>OTOH, a ceramic tab made of AlN shouldn't be that expensive and the > >> >>>>>>>>>>thermal parameters would be great. > >> >>>>>>>>>> > >> >>>>>>>>>> Best regards, Piotr > >> >>>>>>>>> > >> >>>>>>>>>There are TO-220s with isolated tabs. > >> >>>>>>>>> > >> >>>>>>>>>I'll be using two n-fets per channel, in a multichannel programmable > >> >>>>>>>>>load board. If they were isolated, a pair of fets could share heat > >> >>>>>>>>>sinking. > >> >>>>>>>>> > >> >>>>>>>>>Isolated DPAKs with the solder-on straddling heat sinks would be > >> >>>>>>>>>ideal, all surface mount. > >> >>>>>>>> > >> >>>>>>>>Isolated surface-mount parts that share a heatsink. > >> >>>>>>>> > >> >>>>>>>>Surface mount heat sink - it does not compute. > >> >>>>>>>> > >> >>>>>>>>RL > >> >>>>>>> > >> >>>>>>>There are tons of heat sinks in this style: > >> >>>>>>> > >> >>>>>>>https://www.digikey.com/en/products/detail/aavid-thermal-division-of-boyd-corporation/573400D00000G/1625551 > >> >>>>>>> > >> >>>>>>>https://www.digikey.com/en/products/detail/wakefield-vette/217-36CTE6/1033769 > >> >>>>>>> > >> >>>>>>>They straddle a DPAK on the board. One pass through the reflow oven > >> >>>>>>>can solder the fet and the heat sink. > >> >>>>>>> > >> >>>>>>>My programmable load circuit sinks AC or DC. It uses two mosfets. If > >> >>>>>>>the source is AC, they share the dissipation. If DC, only one gets > >> >>>>>>>hot. So it would be great to share the heat sinking. > >> >>>>>>> > >> >>>>>>>Using two non-isolated fets and two heat sinks, the trick would be to > >> >>>>>>>transfer heat between the two but keep them insulated. That could > >> >>>>>>>work. > >> >>>>>> > >> >>>>>> > >> >>>>>>There are lots of isolated tab D-Squared paks (TO-263 ?) Most we > >> >>>>>>use will have a TO-220 and D-Squared package with the same die. > >> >>>>>> > >> >>>>>>We also use D-Pak N channel FETs and P channel D-Pak FETs. > >> >>>>>> > >> >>>>>>Look at IRF part numbers for D-Pak as I remember that we use. > >> >>>>> > >> >>>>>I can't find any isolated dpak fets. Got any part numbers? > >> >>>>> > >> >>>>>There are isolated TO-220s, mostly obsolete. But if I use TO-220s, I > >> >>>>>can bolt them to a big heat sink with insulators. Last resort. > >> >>>>> > >> >>>>>Some PCB layout tricks might couple them thermally but provide > >> >>>>>insulation. Not perfect, but better than nothing. > >> >>>>> > >> >>>>>> > >> >>>>>>And you can heat sink D2Pak FETs. Just have to think about it. > >> >>>>>>We do kilo-watts with D-Squared isolated. 7 lead and 3 lead with the > >> >>>>>>middle lead missing of course. > >> >>>>> > >> >>>>>Got part numbers? > >> >>>> > >> >>>>Uh OH ! My brain COMPLETELY farted ! > >> >>>> > >> >>>>Either that or I was drunk. But I don't even drink ! > >> >>>> > >> >>>>For some reason I got isolated and non-isolated reversed ! > >> >>>> > >> >>>>Ooops. Sorry. > >> >>>> > >> >>>>I have used isolated TO-220s before but I don't think I have seen an > >> >>>>isolated DPAK either. > >> >>>> > >> >>>> > >> >>> > >> >>>Thinking about this again... If a D-Pak has the middle drain pin > >> >>>cut, same as a typical TO-263 D2PAK, how would you access the drain > >> >>>except by the tab ? > >> >>> > >> >> > >> >>It would need a middle pin. > >> >> > >> >>There are some isolated-tab power opamps around, so it's not > >> >>impossible. But I'd better work with standard parts to be safe. > >> > > >> >Yeah, I've only seen TO-220's with the isolated tab. > >> > > >> >IN general, the thermal resistance may or may not be up to par for > >> >your requirements. > >> > > >> >We see FET representatives all the time and will ask next time I see > >> >them. Now you have my curiousity up. > >> > > >> > > >> > > >> Lasse reminded me about AlN thermal jumpers, which really helps the > >> heat sharing situation between the two dpak heat sinks. > >> > >> https://www.dropbox.com/s/l4vums9qosarov4/Dpak_Heat_Sink_2.jpg?raw=1 > >> > >> > >> With 8 programmable load circuits on a board, and some air flow, I'm > >> thinking 10 watts per channel should be OK. > > > >include some through hole pads in the footprint for an easy upgrade with TO220/TO247 > > > > > There are d and d2 pak fets rated for hundreds of watts; my limit is > heat sinking.sure, but adding more heatsinking is a lot easier with a part you can bolt to a heat sink
Reply by ●June 24, 20212021-06-24
On Thu, 24 Jun 2021 09:50:35 -0700 (PDT), Lasse Langwadt Christensen <langwadt@fonz.dk> wrote:>torsdag den 24. juni 2021 kl. 18.40.20 UTC+2 skrev jla...@highlandsniptechnology.com: >> On Thu, 24 Jun 2021 09:19:47 -0700 (PDT), Lasse Langwadt Christensen >> <lang...@fonz.dk> wrote: >> >> >torsdag den 24. juni 2021 kl. 05.46.56 UTC+2 skrev jla...@highlandsniptechnology.com: >> >> On Wed, 23 Jun 2021 11:08:54 -0700, boB <b...@K7IQ.com> wrote: >> >> >> >> >On Wed, 23 Jun 2021 08:51:05 -0700, jla...@highlandsniptechnology.com >> >> >wrote: >> >> > >> >> >>On Tue, 22 Jun 2021 23:40:12 -0700, boB <b...@K7IQ.com> wrote: >> >> >> >> >> >>>On Tue, 22 Jun 2021 21:55:59 -0700, boB <b...@K7IQ.com> wrote: >> >> >>> >> >> >>>>On Tue, 22 Jun 2021 07:08:10 -0700, jla...@highlandsniptechnology.com >> >> >>>>wrote: >> >> >>>> >> >> >>>>>On Mon, 21 Jun 2021 21:25:38 -0700, boB <b...@K7IQ.com> wrote: >> >> >>>>> >> >> >>>>>>On Mon, 21 Jun 2021 15:15:30 -0700, John Larkin >> >> >>>>>><jjla...@highlandtechnology.com> wrote: >> >> >>>>>> >> >> >>>>>>>On Mon, 21 Jun 2021 16:50:04 -0400, legg <le...@nospam.magma.ca> wrote: >> >> >>>>>>> >> >> >>>>>>>>On Mon, 21 Jun 2021 11:00:18 -0700, John Larkin >> >> >>>>>>>><jjla...@highlandtechnology.com> wrote: >> >> >>>>>>>> >> >> >>>>>>>>>On Mon, 21 Jun 2021 19:44:55 +0200, Piotr Wyderski >> >> >>>>>>>>><bom...@protonmail.com> wrote: >> >> >>>>>>>>> >> >> >>>>>>>>>>John Larkin wrote: >> >> >>>>>>>>>> >> >> >>>>>>>>>>> I'm not having much luck searching for isolated-tab mosfets. Ideal >> >> >>>>>>>>>>> would be a dpak n-channel. Any suggestions? >> >> >>>>>>>>>> >> >> >>>>>>>>>>Are there any SMD parts with isolated tab? That would be interesting. >> >> >>>>>>>>>>OTOH, a ceramic tab made of AlN shouldn't be that expensive and the >> >> >>>>>>>>>>thermal parameters would be great. >> >> >>>>>>>>>> >> >> >>>>>>>>>> Best regards, Piotr >> >> >>>>>>>>> >> >> >>>>>>>>>There are TO-220s with isolated tabs. >> >> >>>>>>>>> >> >> >>>>>>>>>I'll be using two n-fets per channel, in a multichannel programmable >> >> >>>>>>>>>load board. If they were isolated, a pair of fets could share heat >> >> >>>>>>>>>sinking. >> >> >>>>>>>>> >> >> >>>>>>>>>Isolated DPAKs with the solder-on straddling heat sinks would be >> >> >>>>>>>>>ideal, all surface mount. >> >> >>>>>>>> >> >> >>>>>>>>Isolated surface-mount parts that share a heatsink. >> >> >>>>>>>> >> >> >>>>>>>>Surface mount heat sink - it does not compute. >> >> >>>>>>>> >> >> >>>>>>>>RL >> >> >>>>>>> >> >> >>>>>>>There are tons of heat sinks in this style: >> >> >>>>>>> >> >> >>>>>>>https://www.digikey.com/en/products/detail/aavid-thermal-division-of-boyd-corporation/573400D00000G/1625551 >> >> >>>>>>> >> >> >>>>>>>https://www.digikey.com/en/products/detail/wakefield-vette/217-36CTE6/1033769 >> >> >>>>>>> >> >> >>>>>>>They straddle a DPAK on the board. One pass through the reflow oven >> >> >>>>>>>can solder the fet and the heat sink. >> >> >>>>>>> >> >> >>>>>>>My programmable load circuit sinks AC or DC. It uses two mosfets. If >> >> >>>>>>>the source is AC, they share the dissipation. If DC, only one gets >> >> >>>>>>>hot. So it would be great to share the heat sinking. >> >> >>>>>>> >> >> >>>>>>>Using two non-isolated fets and two heat sinks, the trick would be to >> >> >>>>>>>transfer heat between the two but keep them insulated. That could >> >> >>>>>>>work. >> >> >>>>>> >> >> >>>>>> >> >> >>>>>>There are lots of isolated tab D-Squared paks (TO-263 ?) Most we >> >> >>>>>>use will have a TO-220 and D-Squared package with the same die. >> >> >>>>>> >> >> >>>>>>We also use D-Pak N channel FETs and P channel D-Pak FETs. >> >> >>>>>> >> >> >>>>>>Look at IRF part numbers for D-Pak as I remember that we use. >> >> >>>>> >> >> >>>>>I can't find any isolated dpak fets. Got any part numbers? >> >> >>>>> >> >> >>>>>There are isolated TO-220s, mostly obsolete. But if I use TO-220s, I >> >> >>>>>can bolt them to a big heat sink with insulators. Last resort. >> >> >>>>> >> >> >>>>>Some PCB layout tricks might couple them thermally but provide >> >> >>>>>insulation. Not perfect, but better than nothing. >> >> >>>>> >> >> >>>>>> >> >> >>>>>>And you can heat sink D2Pak FETs. Just have to think about it. >> >> >>>>>>We do kilo-watts with D-Squared isolated. 7 lead and 3 lead with the >> >> >>>>>>middle lead missing of course. >> >> >>>>> >> >> >>>>>Got part numbers? >> >> >>>> >> >> >>>>Uh OH ! My brain COMPLETELY farted ! >> >> >>>> >> >> >>>>Either that or I was drunk. But I don't even drink ! >> >> >>>> >> >> >>>>For some reason I got isolated and non-isolated reversed ! >> >> >>>> >> >> >>>>Ooops. Sorry. >> >> >>>> >> >> >>>>I have used isolated TO-220s before but I don't think I have seen an >> >> >>>>isolated DPAK either. >> >> >>>> >> >> >>>> >> >> >>> >> >> >>>Thinking about this again... If a D-Pak has the middle drain pin >> >> >>>cut, same as a typical TO-263 D2PAK, how would you access the drain >> >> >>>except by the tab ? >> >> >>> >> >> >> >> >> >>It would need a middle pin. >> >> >> >> >> >>There are some isolated-tab power opamps around, so it's not >> >> >>impossible. But I'd better work with standard parts to be safe. >> >> > >> >> >Yeah, I've only seen TO-220's with the isolated tab. >> >> > >> >> >IN general, the thermal resistance may or may not be up to par for >> >> >your requirements. >> >> > >> >> >We see FET representatives all the time and will ask next time I see >> >> >them. Now you have my curiousity up. >> >> > >> >> > >> >> > >> >> Lasse reminded me about AlN thermal jumpers, which really helps the >> >> heat sharing situation between the two dpak heat sinks. >> >> >> >> https://www.dropbox.com/s/l4vums9qosarov4/Dpak_Heat_Sink_2.jpg?raw=1 >> >> >> >> >> >> With 8 programmable load circuits on a board, and some air flow, I'm >> >> thinking 10 watts per channel should be OK. >> > >> >include some through hole pads in the footprint for an easy upgrade with TO220/TO247 >> > >> > >> There are d and d2 pak fets rated for hundreds of watts; my limit is >> heat sinking. > >sure, but adding more heatsinking is a lot easier with a part you can bolt to a heat sink >The challenge is to do everything with one pick-and-place pass. If I do a single-channel high power dummy load, that would have one big finned heat sink and some TO-247 fets bolted on. Not as much fun to think about, or to build. We just got a selective solder machine, which frees us up to use more thru-hole parts.
Reply by ●June 24, 20212021-06-24
John Larkin wrote:> On Thu, 24 Jun 2021 09:50:35 -0700 (PDT), Lasse Langwadt Christensen > <langwadt@fonz.dk> wrote: > >> torsdag den 24. juni 2021 kl. 18.40.20 UTC+2 skrev jla...@highlandsniptechnology.com: >>> On Thu, 24 Jun 2021 09:19:47 -0700 (PDT), Lasse Langwadt Christensen >>> <lang...@fonz.dk> wrote: >>> >>>> torsdag den 24. juni 2021 kl. 05.46.56 UTC+2 skrev jla...@highlandsniptechnology.com: >>>>> On Wed, 23 Jun 2021 11:08:54 -0700, boB <b...@K7IQ.com> wrote: >>>>> >>>>>> On Wed, 23 Jun 2021 08:51:05 -0700, jla...@highlandsniptechnology.com >>>>>> wrote: >>>>>> >>>>>>> On Tue, 22 Jun 2021 23:40:12 -0700, boB <b...@K7IQ.com> wrote: >>>>>>> >>>>>>>> On Tue, 22 Jun 2021 21:55:59 -0700, boB <b...@K7IQ.com> wrote: >>>>>>>> >>>>>>>>> On Tue, 22 Jun 2021 07:08:10 -0700, jla...@highlandsniptechnology.com >>>>>>>>> wrote: >>>>>>>>> >>>>>>>>>> On Mon, 21 Jun 2021 21:25:38 -0700, boB <b...@K7IQ.com> wrote: >>>>>>>>>> >>>>>>>>>>> On Mon, 21 Jun 2021 15:15:30 -0700, John Larkin >>>>>>>>>>> <jjla...@highlandtechnology.com> wrote: >>>>>>>>>>> >>>>>>>>>>>> On Mon, 21 Jun 2021 16:50:04 -0400, legg <le...@nospam.magma.ca> wrote: >>>>>>>>>>>> >>>>>>>>>>>>> On Mon, 21 Jun 2021 11:00:18 -0700, John Larkin >>>>>>>>>>>>> <jjla...@highlandtechnology.com> wrote: >>>>>>>>>>>>> >>>>>>>>>>>>>> On Mon, 21 Jun 2021 19:44:55 +0200, Piotr Wyderski >>>>>>>>>>>>>> <bom...@protonmail.com> wrote: >>>>>>>>>>>>>> >>>>>>>>>>>>>>> John Larkin wrote: >>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> I'm not having much luck searching for isolated-tab mosfets. Ideal >>>>>>>>>>>>>>>> would be a dpak n-channel. Any suggestions? >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> Are there any SMD parts with isolated tab? That would be interesting. >>>>>>>>>>>>>>> OTOH, a ceramic tab made of AlN shouldn't be that expensive and the >>>>>>>>>>>>>>> thermal parameters would be great. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> Best regards, Piotr >>>>>>>>>>>>>> >>>>>>>>>>>>>> There are TO-220s with isolated tabs. >>>>>>>>>>>>>> >>>>>>>>>>>>>> I'll be using two n-fets per channel, in a multichannel programmable >>>>>>>>>>>>>> load board. If they were isolated, a pair of fets could share heat >>>>>>>>>>>>>> sinking. >>>>>>>>>>>>>> >>>>>>>>>>>>>> Isolated DPAKs with the solder-on straddling heat sinks would be >>>>>>>>>>>>>> ideal, all surface mount. >>>>>>>>>>>>> >>>>>>>>>>>>> Isolated surface-mount parts that share a heatsink. >>>>>>>>>>>>> >>>>>>>>>>>>> Surface mount heat sink - it does not compute. >>>>>>>>>>>>> >>>>>>>>>>>>> RL >>>>>>>>>>>> >>>>>>>>>>>> There are tons of heat sinks in this style: >>>>>>>>>>>> >>>>>>>>>>>> https://www.digikey.com/en/products/detail/aavid-thermal-division-of-boyd-corporation/573400D00000G/1625551 >>>>>>>>>>>> >>>>>>>>>>>> https://www.digikey.com/en/products/detail/wakefield-vette/217-36CTE6/1033769 >>>>>>>>>>>> >>>>>>>>>>>> They straddle a DPAK on the board. One pass through the reflow oven >>>>>>>>>>>> can solder the fet and the heat sink. >>>>>>>>>>>> >>>>>>>>>>>> My programmable load circuit sinks AC or DC. It uses two mosfets. If >>>>>>>>>>>> the source is AC, they share the dissipation. If DC, only one gets >>>>>>>>>>>> hot. So it would be great to share the heat sinking. >>>>>>>>>>>> >>>>>>>>>>>> Using two non-isolated fets and two heat sinks, the trick would be to >>>>>>>>>>>> transfer heat between the two but keep them insulated. That could >>>>>>>>>>>> work. >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> There are lots of isolated tab D-Squared paks (TO-263 ?) Most we >>>>>>>>>>> use will have a TO-220 and D-Squared package with the same die. >>>>>>>>>>> >>>>>>>>>>> We also use D-Pak N channel FETs and P channel D-Pak FETs. >>>>>>>>>>> >>>>>>>>>>> Look at IRF part numbers for D-Pak as I remember that we use. >>>>>>>>>> >>>>>>>>>> I can't find any isolated dpak fets. Got any part numbers? >>>>>>>>>> >>>>>>>>>> There are isolated TO-220s, mostly obsolete. But if I use TO-220s, I >>>>>>>>>> can bolt them to a big heat sink with insulators. Last resort. >>>>>>>>>> >>>>>>>>>> Some PCB layout tricks might couple them thermally but provide >>>>>>>>>> insulation. Not perfect, but better than nothing. >>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> And you can heat sink D2Pak FETs. Just have to think about it. >>>>>>>>>>> We do kilo-watts with D-Squared isolated. 7 lead and 3 lead with the >>>>>>>>>>> middle lead missing of course. >>>>>>>>>> >>>>>>>>>> Got part numbers? >>>>>>>>> >>>>>>>>> Uh OH ! My brain COMPLETELY farted ! >>>>>>>>> >>>>>>>>> Either that or I was drunk. But I don't even drink ! >>>>>>>>> >>>>>>>>> For some reason I got isolated and non-isolated reversed ! >>>>>>>>> >>>>>>>>> Ooops. Sorry. >>>>>>>>> >>>>>>>>> I have used isolated TO-220s before but I don't think I have seen an >>>>>>>>> isolated DPAK either. >>>>>>>>> >>>>>>>>> >>>>>>>> >>>>>>>> Thinking about this again... If a D-Pak has the middle drain pin >>>>>>>> cut, same as a typical TO-263 D2PAK, how would you access the drain >>>>>>>> except by the tab ? >>>>>>>> >>>>>>> >>>>>>> It would need a middle pin. >>>>>>> >>>>>>> There are some isolated-tab power opamps around, so it's not >>>>>>> impossible. But I'd better work with standard parts to be safe. >>>>>> >>>>>> Yeah, I've only seen TO-220's with the isolated tab. >>>>>> >>>>>> IN general, the thermal resistance may or may not be up to par for >>>>>> your requirements. >>>>>> >>>>>> We see FET representatives all the time and will ask next time I see >>>>>> them. Now you have my curiousity up. >>>>>> >>>>>> >>>>>> >>>>> Lasse reminded me about AlN thermal jumpers, which really helps the >>>>> heat sharing situation between the two dpak heat sinks. >>>>> >>>>> https://www.dropbox.com/s/l4vums9qosarov4/Dpak_Heat_Sink_2.jpg?raw=1 >>>>> >>>>> >>>>> With 8 programmable load circuits on a board, and some air flow, I'm >>>>> thinking 10 watts per channel should be OK. >>>> >>>> include some through hole pads in the footprint for an easy upgrade with TO220/TO247 >>>> >>>> >>> There are d and d2 pak fets rated for hundreds of watts; my limit is >>> heat sinking. >> >> sure, but adding more heatsinking is a lot easier with a part you can bolt to a heat sink >> > > The challenge is to do everything with one pick-and-place pass. > > If I do a single-channel high power dummy load, that would have one > big finned heat sink and some TO-247 fets bolted on. Not as much fun > to think about, or to build. > > We just got a selective solder machine, which frees us up to use more > thru-hole parts. >TCA0372Ps can't be far behind. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●June 25, 20212021-06-25
On Thu, 24 Jun 2021 15:47:09 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>John Larkin wrote: >> On Thu, 24 Jun 2021 09:50:35 -0700 (PDT), Lasse Langwadt Christensen >> <langwadt@fonz.dk> wrote: >> >>> torsdag den 24. juni 2021 kl. 18.40.20 UTC+2 skrev jla...@highlandsniptechnology.com: >>>> On Thu, 24 Jun 2021 09:19:47 -0700 (PDT), Lasse Langwadt Christensen >>>> <lang...@fonz.dk> wrote: >>>> >>>>> torsdag den 24. juni 2021 kl. 05.46.56 UTC+2 skrev jla...@highlandsniptechnology.com: >>>>>> On Wed, 23 Jun 2021 11:08:54 -0700, boB <b...@K7IQ.com> wrote: >>>>>> >>>>>>> On Wed, 23 Jun 2021 08:51:05 -0700, jla...@highlandsniptechnology.com >>>>>>> wrote: >>>>>>> >>>>>>>> On Tue, 22 Jun 2021 23:40:12 -0700, boB <b...@K7IQ.com> wrote: >>>>>>>> >>>>>>>>> On Tue, 22 Jun 2021 21:55:59 -0700, boB <b...@K7IQ.com> wrote: >>>>>>>>> >>>>>>>>>> On Tue, 22 Jun 2021 07:08:10 -0700, jla...@highlandsniptechnology.com >>>>>>>>>> wrote: >>>>>>>>>> >>>>>>>>>>> On Mon, 21 Jun 2021 21:25:38 -0700, boB <b...@K7IQ.com> wrote: >>>>>>>>>>> >>>>>>>>>>>> On Mon, 21 Jun 2021 15:15:30 -0700, John Larkin >>>>>>>>>>>> <jjla...@highlandtechnology.com> wrote: >>>>>>>>>>>> >>>>>>>>>>>>> On Mon, 21 Jun 2021 16:50:04 -0400, legg <le...@nospam.magma.ca> wrote: >>>>>>>>>>>>> >>>>>>>>>>>>>> On Mon, 21 Jun 2021 11:00:18 -0700, John Larkin >>>>>>>>>>>>>> <jjla...@highlandtechnology.com> wrote: >>>>>>>>>>>>>> >>>>>>>>>>>>>>> On Mon, 21 Jun 2021 19:44:55 +0200, Piotr Wyderski >>>>>>>>>>>>>>> <bom...@protonmail.com> wrote: >>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> John Larkin wrote: >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> I'm not having much luck searching for isolated-tab mosfets. Ideal >>>>>>>>>>>>>>>>> would be a dpak n-channel. Any suggestions? >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> Are there any SMD parts with isolated tab? That would be interesting. >>>>>>>>>>>>>>>> OTOH, a ceramic tab made of AlN shouldn't be that expensive and the >>>>>>>>>>>>>>>> thermal parameters would be great. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> Best regards, Piotr >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> There are TO-220s with isolated tabs. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> I'll be using two n-fets per channel, in a multichannel programmable >>>>>>>>>>>>>>> load board. If they were isolated, a pair of fets could share heat >>>>>>>>>>>>>>> sinking. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> Isolated DPAKs with the solder-on straddling heat sinks would be >>>>>>>>>>>>>>> ideal, all surface mount. >>>>>>>>>>>>>> >>>>>>>>>>>>>> Isolated surface-mount parts that share a heatsink. >>>>>>>>>>>>>> >>>>>>>>>>>>>> Surface mount heat sink - it does not compute. >>>>>>>>>>>>>> >>>>>>>>>>>>>> RL >>>>>>>>>>>>> >>>>>>>>>>>>> There are tons of heat sinks in this style: >>>>>>>>>>>>> >>>>>>>>>>>>> https://www.digikey.com/en/products/detail/aavid-thermal-division-of-boyd-corporation/573400D00000G/1625551 >>>>>>>>>>>>> >>>>>>>>>>>>> https://www.digikey.com/en/products/detail/wakefield-vette/217-36CTE6/1033769 >>>>>>>>>>>>> >>>>>>>>>>>>> They straddle a DPAK on the board. One pass through the reflow oven >>>>>>>>>>>>> can solder the fet and the heat sink. >>>>>>>>>>>>> >>>>>>>>>>>>> My programmable load circuit sinks AC or DC. It uses two mosfets. If >>>>>>>>>>>>> the source is AC, they share the dissipation. If DC, only one gets >>>>>>>>>>>>> hot. So it would be great to share the heat sinking. >>>>>>>>>>>>> >>>>>>>>>>>>> Using two non-isolated fets and two heat sinks, the trick would be to >>>>>>>>>>>>> transfer heat between the two but keep them insulated. That could >>>>>>>>>>>>> work. >>>>>>>>>>>> >>>>>>>>>>>> >>>>>>>>>>>> There are lots of isolated tab D-Squared paks (TO-263 ?) Most we >>>>>>>>>>>> use will have a TO-220 and D-Squared package with the same die. >>>>>>>>>>>> >>>>>>>>>>>> We also use D-Pak N channel FETs and P channel D-Pak FETs. >>>>>>>>>>>> >>>>>>>>>>>> Look at IRF part numbers for D-Pak as I remember that we use. >>>>>>>>>>> >>>>>>>>>>> I can't find any isolated dpak fets. Got any part numbers? >>>>>>>>>>> >>>>>>>>>>> There are isolated TO-220s, mostly obsolete. But if I use TO-220s, I >>>>>>>>>>> can bolt them to a big heat sink with insulators. Last resort. >>>>>>>>>>> >>>>>>>>>>> Some PCB layout tricks might couple them thermally but provide >>>>>>>>>>> insulation. Not perfect, but better than nothing. >>>>>>>>>>> >>>>>>>>>>>> >>>>>>>>>>>> And you can heat sink D2Pak FETs. Just have to think about it. >>>>>>>>>>>> We do kilo-watts with D-Squared isolated. 7 lead and 3 lead with the >>>>>>>>>>>> middle lead missing of course. >>>>>>>>>>> >>>>>>>>>>> Got part numbers? >>>>>>>>>> >>>>>>>>>> Uh OH ! My brain COMPLETELY farted ! >>>>>>>>>> >>>>>>>>>> Either that or I was drunk. But I don't even drink ! >>>>>>>>>> >>>>>>>>>> For some reason I got isolated and non-isolated reversed ! >>>>>>>>>> >>>>>>>>>> Ooops. Sorry. >>>>>>>>>> >>>>>>>>>> I have used isolated TO-220s before but I don't think I have seen an >>>>>>>>>> isolated DPAK either. >>>>>>>>>> >>>>>>>>>> >>>>>>>>> >>>>>>>>> Thinking about this again... If a D-Pak has the middle drain pin >>>>>>>>> cut, same as a typical TO-263 D2PAK, how would you access the drain >>>>>>>>> except by the tab ? >>>>>>>>> >>>>>>>> >>>>>>>> It would need a middle pin. >>>>>>>> >>>>>>>> There are some isolated-tab power opamps around, so it's not >>>>>>>> impossible. But I'd better work with standard parts to be safe. >>>>>>> >>>>>>> Yeah, I've only seen TO-220's with the isolated tab. >>>>>>> >>>>>>> IN general, the thermal resistance may or may not be up to par for >>>>>>> your requirements. >>>>>>> >>>>>>> We see FET representatives all the time and will ask next time I see >>>>>>> them. Now you have my curiousity up. >>>>>>> >>>>>>> >>>>>>> >>>>>> Lasse reminded me about AlN thermal jumpers, which really helps the >>>>>> heat sharing situation between the two dpak heat sinks. >>>>>> >>>>>> https://www.dropbox.com/s/l4vums9qosarov4/Dpak_Heat_Sink_2.jpg?raw=1 >>>>>> >>>>>> >>>>>> With 8 programmable load circuits on a board, and some air flow, I'm >>>>>> thinking 10 watts per channel should be OK. >>>>> >>>>> include some through hole pads in the footprint for an easy upgrade with TO220/TO247 >>>>> >>>>> >>>> There are d and d2 pak fets rated for hundreds of watts; my limit is >>>> heat sinking. >>> >>> sure, but adding more heatsinking is a lot easier with a part you can bolt to a heat sink >>> >> >> The challenge is to do everything with one pick-and-place pass. >> >> If I do a single-channel high power dummy load, that would have one >> big finned heat sink and some TO-247 fets bolted on. Not as much fun >> to think about, or to build. >> >> We just got a selective solder machine, which frees us up to use more >> thru-hole parts. >> > >TCA0372Ps can't be far behind. > >Cheers > >Phil HobbsDigikey shows it as obsolete with 318,160 in stock. Digikey is not making sense lately. The problem with dips is just soldering, it's insertion. -- John Larkin Highland Technology, Inc The best designs are necessarily accidental.
Reply by ●June 27, 20212021-06-27
On Thu, 24 Jun 2021 20:41:25 -0700, jlarkin@highlandsniptechnology.com wrote:>On Thu, 24 Jun 2021 15:47:09 -0400, Phil Hobbs ><pcdhSpamMeSenseless@electrooptical.net> wrote: > >>John Larkin wrote: >>> On Thu, 24 Jun 2021 09:50:35 -0700 (PDT), Lasse Langwadt Christensen >>> <langwadt@fonz.dk> wrote: >>> >>>> torsdag den 24. juni 2021 kl. 18.40.20 UTC+2 skrev jla...@highlandsniptechnology.com: >>>>> On Thu, 24 Jun 2021 09:19:47 -0700 (PDT), Lasse Langwadt Christensen >>>>> <lang...@fonz.dk> wrote: >>>>> >>>>>> torsdag den 24. juni 2021 kl. 05.46.56 UTC+2 skrev jla...@highlandsniptechnology.com: >>>>>>> On Wed, 23 Jun 2021 11:08:54 -0700, boB <b...@K7IQ.com> wrote: >>>>>>> >>>>>>>> On Wed, 23 Jun 2021 08:51:05 -0700, jla...@highlandsniptechnology.com >>>>>>>> wrote: >>>>>>>> >>>>>>>>> On Tue, 22 Jun 2021 23:40:12 -0700, boB <b...@K7IQ.com> wrote: >>>>>>>>> >>>>>>>>>> On Tue, 22 Jun 2021 21:55:59 -0700, boB <b...@K7IQ.com> wrote: >>>>>>>>>> >>>>>>>>>>> On Tue, 22 Jun 2021 07:08:10 -0700, jla...@highlandsniptechnology.com >>>>>>>>>>> wrote: >>>>>>>>>>> >>>>>>>>>>>> On Mon, 21 Jun 2021 21:25:38 -0700, boB <b...@K7IQ.com> wrote: >>>>>>>>>>>> >>>>>>>>>>>>> On Mon, 21 Jun 2021 15:15:30 -0700, John Larkin >>>>>>>>>>>>> <jjla...@highlandtechnology.com> wrote: >>>>>>>>>>>>> >>>>>>>>>>>>>> On Mon, 21 Jun 2021 16:50:04 -0400, legg <le...@nospam.magma.ca> wrote: >>>>>>>>>>>>>> >>>>>>>>>>>>>>> On Mon, 21 Jun 2021 11:00:18 -0700, John Larkin >>>>>>>>>>>>>>> <jjla...@highlandtechnology.com> wrote: >>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> On Mon, 21 Jun 2021 19:44:55 +0200, Piotr Wyderski >>>>>>>>>>>>>>>> <bom...@protonmail.com> wrote: >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> John Larkin wrote: >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> I'm not having much luck searching for isolated-tab mosfets. Ideal >>>>>>>>>>>>>>>>>> would be a dpak n-channel. Any suggestions? >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> Are there any SMD parts with isolated tab? That would be interesting. >>>>>>>>>>>>>>>>> OTOH, a ceramic tab made of AlN shouldn't be that expensive and the >>>>>>>>>>>>>>>>> thermal parameters would be great. >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> Best regards, Piotr >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> There are TO-220s with isolated tabs. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> I'll be using two n-fets per channel, in a multichannel programmable >>>>>>>>>>>>>>>> load board. If they were isolated, a pair of fets could share heat >>>>>>>>>>>>>>>> sinking. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> Isolated DPAKs with the solder-on straddling heat sinks would be >>>>>>>>>>>>>>>> ideal, all surface mount. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> Isolated surface-mount parts that share a heatsink. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> Surface mount heat sink - it does not compute. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> RL >>>>>>>>>>>>>> >>>>>>>>>>>>>> There are tons of heat sinks in this style: >>>>>>>>>>>>>> >>>>>>>>>>>>>> https://www.digikey.com/en/products/detail/aavid-thermal-division-of-boyd-corporation/573400D00000G/1625551 >>>>>>>>>>>>>> >>>>>>>>>>>>>> https://www.digikey.com/en/products/detail/wakefield-vette/217-36CTE6/1033769 >>>>>>>>>>>>>> >>>>>>>>>>>>>> They straddle a DPAK on the board. One pass through the reflow oven >>>>>>>>>>>>>> can solder the fet and the heat sink. >>>>>>>>>>>>>> >>>>>>>>>>>>>> My programmable load circuit sinks AC or DC. It uses two mosfets. If >>>>>>>>>>>>>> the source is AC, they share the dissipation. If DC, only one gets >>>>>>>>>>>>>> hot. So it would be great to share the heat sinking. >>>>>>>>>>>>>> >>>>>>>>>>>>>> Using two non-isolated fets and two heat sinks, the trick would be to >>>>>>>>>>>>>> transfer heat between the two but keep them insulated. That could >>>>>>>>>>>>>> work. >>>>>>>>>>>>> >>>>>>>>>>>>> >>>>>>>>>>>>> There are lots of isolated tab D-Squared paks (TO-263 ?) Most we >>>>>>>>>>>>> use will have a TO-220 and D-Squared package with the same die. >>>>>>>>>>>>> >>>>>>>>>>>>> We also use D-Pak N channel FETs and P channel D-Pak FETs. >>>>>>>>>>>>> >>>>>>>>>>>>> Look at IRF part numbers for D-Pak as I remember that we use. >>>>>>>>>>>> >>>>>>>>>>>> I can't find any isolated dpak fets. Got any part numbers? >>>>>>>>>>>> >>>>>>>>>>>> There are isolated TO-220s, mostly obsolete. But if I use TO-220s, I >>>>>>>>>>>> can bolt them to a big heat sink with insulators. Last resort. >>>>>>>>>>>> >>>>>>>>>>>> Some PCB layout tricks might couple them thermally but provide >>>>>>>>>>>> insulation. Not perfect, but better than nothing. >>>>>>>>>>>> >>>>>>>>>>>>> >>>>>>>>>>>>> And you can heat sink D2Pak FETs. Just have to think about it. >>>>>>>>>>>>> We do kilo-watts with D-Squared isolated. 7 lead and 3 lead with the >>>>>>>>>>>>> middle lead missing of course. >>>>>>>>>>>> >>>>>>>>>>>> Got part numbers? >>>>>>>>>>> >>>>>>>>>>> Uh OH ! My brain COMPLETELY farted ! >>>>>>>>>>> >>>>>>>>>>> Either that or I was drunk. But I don't even drink ! >>>>>>>>>>> >>>>>>>>>>> For some reason I got isolated and non-isolated reversed ! >>>>>>>>>>> >>>>>>>>>>> Ooops. Sorry. >>>>>>>>>>> >>>>>>>>>>> I have used isolated TO-220s before but I don't think I have seen an >>>>>>>>>>> isolated DPAK either. >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>> >>>>>>>>>> Thinking about this again... If a D-Pak has the middle drain pin >>>>>>>>>> cut, same as a typical TO-263 D2PAK, how would you access the drain >>>>>>>>>> except by the tab ? >>>>>>>>>> >>>>>>>>> >>>>>>>>> It would need a middle pin. >>>>>>>>> >>>>>>>>> There are some isolated-tab power opamps around, so it's not >>>>>>>>> impossible. But I'd better work with standard parts to be safe. >>>>>>>> >>>>>>>> Yeah, I've only seen TO-220's with the isolated tab. >>>>>>>> >>>>>>>> IN general, the thermal resistance may or may not be up to par for >>>>>>>> your requirements. >>>>>>>> >>>>>>>> We see FET representatives all the time and will ask next time I see >>>>>>>> them. Now you have my curiousity up. >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>> Lasse reminded me about AlN thermal jumpers, which really helps the >>>>>>> heat sharing situation between the two dpak heat sinks. >>>>>>> >>>>>>> https://www.dropbox.com/s/l4vums9qosarov4/Dpak_Heat_Sink_2.jpg?raw=1 >>>>>>> >>>>>>> >>>>>>> With 8 programmable load circuits on a board, and some air flow, I'm >>>>>>> thinking 10 watts per channel should be OK. >>>>>> >>>>>> include some through hole pads in the footprint for an easy upgrade with TO220/TO247 >>>>>> >>>>>> >>>>> There are d and d2 pak fets rated for hundreds of watts; my limit is >>>>> heat sinking. >>>> >>>> sure, but adding more heatsinking is a lot easier with a part you can bolt to a heat sink >>>> >>> >>> The challenge is to do everything with one pick-and-place pass. >>> >>> If I do a single-channel high power dummy load, that would have one >>> big finned heat sink and some TO-247 fets bolted on. Not as much fun >>> to think about, or to build. >>> >>> We just got a selective solder machine, which frees us up to use more >>> thru-hole parts. >>> >> >>TCA0372Ps can't be far behind. >> >>Cheers >> >>Phil Hobbs > >Digikey shows it as obsolete with 318,160 in stock. > >Digikey is not making sense lately. > >The problem with dips is just soldering, it's insertion.Hint: You can also put a heat-sink on the bottom side of the PCB (opposite side than the FET's tab is on.) We do it with D2PAKs. Should work OK with DPAKs as well. Just gotta think about it for a few minutes. Mounting directly to a heat-sink is better but not bad this way either. boB
Reply by ●June 27, 20212021-06-27
On Sat, 26 Jun 2021 23:18:20 -0700, boB <boB@K7IQ.com> wrote:>On Thu, 24 Jun 2021 20:41:25 -0700, jlarkin@highlandsniptechnology.com >wrote: > >>On Thu, 24 Jun 2021 15:47:09 -0400, Phil Hobbs >><pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>>John Larkin wrote: >>>> On Thu, 24 Jun 2021 09:50:35 -0700 (PDT), Lasse Langwadt Christensen >>>> <langwadt@fonz.dk> wrote: >>>> >>>>> torsdag den 24. juni 2021 kl. 18.40.20 UTC+2 skrev jla...@highlandsniptechnology.com: >>>>>> On Thu, 24 Jun 2021 09:19:47 -0700 (PDT), Lasse Langwadt Christensen >>>>>> <lang...@fonz.dk> wrote: >>>>>> >>>>>>> torsdag den 24. juni 2021 kl. 05.46.56 UTC+2 skrev jla...@highlandsniptechnology.com: >>>>>>>> On Wed, 23 Jun 2021 11:08:54 -0700, boB <b...@K7IQ.com> wrote: >>>>>>>> >>>>>>>>> On Wed, 23 Jun 2021 08:51:05 -0700, jla...@highlandsniptechnology.com >>>>>>>>> wrote: >>>>>>>>> >>>>>>>>>> On Tue, 22 Jun 2021 23:40:12 -0700, boB <b...@K7IQ.com> wrote: >>>>>>>>>> >>>>>>>>>>> On Tue, 22 Jun 2021 21:55:59 -0700, boB <b...@K7IQ.com> wrote: >>>>>>>>>>> >>>>>>>>>>>> On Tue, 22 Jun 2021 07:08:10 -0700, jla...@highlandsniptechnology.com >>>>>>>>>>>> wrote: >>>>>>>>>>>> >>>>>>>>>>>>> On Mon, 21 Jun 2021 21:25:38 -0700, boB <b...@K7IQ.com> wrote: >>>>>>>>>>>>> >>>>>>>>>>>>>> On Mon, 21 Jun 2021 15:15:30 -0700, John Larkin >>>>>>>>>>>>>> <jjla...@highlandtechnology.com> wrote: >>>>>>>>>>>>>> >>>>>>>>>>>>>>> On Mon, 21 Jun 2021 16:50:04 -0400, legg <le...@nospam.magma.ca> wrote: >>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> On Mon, 21 Jun 2021 11:00:18 -0700, John Larkin >>>>>>>>>>>>>>>> <jjla...@highlandtechnology.com> wrote: >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> On Mon, 21 Jun 2021 19:44:55 +0200, Piotr Wyderski >>>>>>>>>>>>>>>>> <bom...@protonmail.com> wrote: >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> John Larkin wrote: >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> I'm not having much luck searching for isolated-tab mosfets. Ideal >>>>>>>>>>>>>>>>>>> would be a dpak n-channel. Any suggestions? >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> Are there any SMD parts with isolated tab? That would be interesting. >>>>>>>>>>>>>>>>>> OTOH, a ceramic tab made of AlN shouldn't be that expensive and the >>>>>>>>>>>>>>>>>> thermal parameters would be great. >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> Best regards, Piotr >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> There are TO-220s with isolated tabs. >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> I'll be using two n-fets per channel, in a multichannel programmable >>>>>>>>>>>>>>>>> load board. If they were isolated, a pair of fets could share heat >>>>>>>>>>>>>>>>> sinking. >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> Isolated DPAKs with the solder-on straddling heat sinks would be >>>>>>>>>>>>>>>>> ideal, all surface mount. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> Isolated surface-mount parts that share a heatsink. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> Surface mount heat sink - it does not compute. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> RL >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> There are tons of heat sinks in this style: >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> https://www.digikey.com/en/products/detail/aavid-thermal-division-of-boyd-corporation/573400D00000G/1625551 >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> https://www.digikey.com/en/products/detail/wakefield-vette/217-36CTE6/1033769 >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> They straddle a DPAK on the board. One pass through the reflow oven >>>>>>>>>>>>>>> can solder the fet and the heat sink. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> My programmable load circuit sinks AC or DC. It uses two mosfets. If >>>>>>>>>>>>>>> the source is AC, they share the dissipation. If DC, only one gets >>>>>>>>>>>>>>> hot. So it would be great to share the heat sinking. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> Using two non-isolated fets and two heat sinks, the trick would be to >>>>>>>>>>>>>>> transfer heat between the two but keep them insulated. That could >>>>>>>>>>>>>>> work. >>>>>>>>>>>>>> >>>>>>>>>>>>>> >>>>>>>>>>>>>> There are lots of isolated tab D-Squared paks (TO-263 ?) Most we >>>>>>>>>>>>>> use will have a TO-220 and D-Squared package with the same die. >>>>>>>>>>>>>> >>>>>>>>>>>>>> We also use D-Pak N channel FETs and P channel D-Pak FETs. >>>>>>>>>>>>>> >>>>>>>>>>>>>> Look at IRF part numbers for D-Pak as I remember that we use. >>>>>>>>>>>>> >>>>>>>>>>>>> I can't find any isolated dpak fets. Got any part numbers? >>>>>>>>>>>>> >>>>>>>>>>>>> There are isolated TO-220s, mostly obsolete. But if I use TO-220s, I >>>>>>>>>>>>> can bolt them to a big heat sink with insulators. Last resort. >>>>>>>>>>>>> >>>>>>>>>>>>> Some PCB layout tricks might couple them thermally but provide >>>>>>>>>>>>> insulation. Not perfect, but better than nothing. >>>>>>>>>>>>> >>>>>>>>>>>>>> >>>>>>>>>>>>>> And you can heat sink D2Pak FETs. Just have to think about it. >>>>>>>>>>>>>> We do kilo-watts with D-Squared isolated. 7 lead and 3 lead with the >>>>>>>>>>>>>> middle lead missing of course. >>>>>>>>>>>>> >>>>>>>>>>>>> Got part numbers? >>>>>>>>>>>> >>>>>>>>>>>> Uh OH ! My brain COMPLETELY farted ! >>>>>>>>>>>> >>>>>>>>>>>> Either that or I was drunk. But I don't even drink ! >>>>>>>>>>>> >>>>>>>>>>>> For some reason I got isolated and non-isolated reversed ! >>>>>>>>>>>> >>>>>>>>>>>> Ooops. Sorry. >>>>>>>>>>>> >>>>>>>>>>>> I have used isolated TO-220s before but I don't think I have seen an >>>>>>>>>>>> isolated DPAK either. >>>>>>>>>>>> >>>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> Thinking about this again... If a D-Pak has the middle drain pin >>>>>>>>>>> cut, same as a typical TO-263 D2PAK, how would you access the drain >>>>>>>>>>> except by the tab ? >>>>>>>>>>> >>>>>>>>>> >>>>>>>>>> It would need a middle pin. >>>>>>>>>> >>>>>>>>>> There are some isolated-tab power opamps around, so it's not >>>>>>>>>> impossible. But I'd better work with standard parts to be safe. >>>>>>>>> >>>>>>>>> Yeah, I've only seen TO-220's with the isolated tab. >>>>>>>>> >>>>>>>>> IN general, the thermal resistance may or may not be up to par for >>>>>>>>> your requirements. >>>>>>>>> >>>>>>>>> We see FET representatives all the time and will ask next time I see >>>>>>>>> them. Now you have my curiousity up. >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>> Lasse reminded me about AlN thermal jumpers, which really helps the >>>>>>>> heat sharing situation between the two dpak heat sinks. >>>>>>>> >>>>>>>> https://www.dropbox.com/s/l4vums9qosarov4/Dpak_Heat_Sink_2.jpg?raw=1 >>>>>>>> >>>>>>>> >>>>>>>> With 8 programmable load circuits on a board, and some air flow, I'm >>>>>>>> thinking 10 watts per channel should be OK. >>>>>>> >>>>>>> include some through hole pads in the footprint for an easy upgrade with TO220/TO247 >>>>>>> >>>>>>> >>>>>> There are d and d2 pak fets rated for hundreds of watts; my limit is >>>>>> heat sinking. >>>>> >>>>> sure, but adding more heatsinking is a lot easier with a part you can bolt to a heat sink >>>>> >>>> >>>> The challenge is to do everything with one pick-and-place pass. >>>> >>>> If I do a single-channel high power dummy load, that would have one >>>> big finned heat sink and some TO-247 fets bolted on. Not as much fun >>>> to think about, or to build. >>>> >>>> We just got a selective solder machine, which frees us up to use more >>>> thru-hole parts. >>>> >>> >>>TCA0372Ps can't be far behind. >>> >>>Cheers >>> >>>Phil Hobbs >> >>Digikey shows it as obsolete with 318,160 in stock. >> >>Digikey is not making sense lately. >> >>The problem with dips is just soldering, it's insertion. > > >Hint: You can also put a heat-sink on the bottom side of the PCB >(opposite side than the FET's tab is on.) > >We do it with D2PAKs. Should work OK with DPAKs as well. > >Just gotta think about it for a few minutes.Few minutes!!!??? We've been obcessing on this for weeks.> >Mounting directly to a heat-sink is better but not bad this way >either.I'd like to pick-and-place everything, fets and heatsinks both, on the 8-channel load board. We can have a giant extruded heat sink and a few TO-247's on the high power, single channel version. We're thinking 10 boards on 1.2" centers, and won't allow tall parts on the bottom. Heat sinks on the bottom wouldn't help much anyhow, because it's hard to transport the heat from the fets on the top side. Here's the general idea: https://www.dropbox.com/s/2urukk7y30cxr70/P940_Jun_25.jpg?raw=1 Looks like we'll move the fans to the front panel, blowing out. Hand warmers.> >boB > > > >-- John Larkin Highland Technology, Inc The best designs are necessarily accidental.
