I'm not having much luck searching for isolated-tab mosfets. Ideal would be a dpak n-channel. Any suggestions? -- John Larkin Highland Technology, Inc trk The cork popped merrily, and Lord Peter rose to his feet. "Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"
isolated mosfets
Started by ●June 21, 2021
Reply by ●June 21, 20212021-06-21
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
Reply by ●June 21, 20212021-06-21
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, PiotrThere 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. -- John Larkin Highland Technology, Inc trk The cork popped merrily, and Lord Peter rose to his feet. "Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"
Reply by ●June 21, 20212021-06-21
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
Reply by ●June 21, 20212021-06-21
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.Easier to buy an isolated heatsink. More versatile. RL
Reply by ●June 21, 20212021-06-21
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. > >RLThere 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. -- John Larkin Highland Technology, Inc trk The cork popped merrily, and Lord Peter rose to his feet. "Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"
Reply by ●June 22, 20212021-06-22
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. 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.
Reply by ●June 22, 20212021-06-22
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? -- John Larkin Highland Technology, Inc The best designs are necessarily accidental.
Reply by ●June 22, 20212021-06-22
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.I have only used those types of parts in situations where, in the past, a clip-on might be used for through-hole parts.Nothing over a watt or two. None are made for coupling heat sources of significance. They are expensive, difficult to reflow and largely ineffective without forced air. I've only used isolated TO220 (not TO263) where emc prohibited capacitive coupling - and then only TO220F (plastic) - nothing with an internal ceramic wafer ($$$)- something you'd need to retain the SMD mounting methods of TO263 (D2). AC applications will distribute heat because they are AC. If you mean reversible DC, then equal heat distribution is worth persuing. You seem to have a lot of small heat sources in mind. These are the kind that are least affected by an electrical isolation barrier. RL
Reply by ●June 22, 20212021-06-22
legg wrote:> Isolated surface-mount parts that share a heatsink. > > Surface mount heat sink - it does not compute.Actually, it does. In one of my projects I had a very similar set or requirements. A ceramic substrate PCB, ideally made of AlN, would be a perfect solution -- it is a great insulator and a decent heat conductor. Unfortunately, even the price of alumina turned out to be a killer. Best regards, Piotr
