Did some searching and didn't come across anything specifically applicable to my situation - happy to take pointers if I missed it!
I've got a couple of pass mosfets in my power supply design that will be dissipating around 7W apiece. They're in a TO-220 package (although I'm open to others), and have a 62.5C/W thermal resistance in free air, so they need to be sinked.
I obviously can't just stick them inside a closed chassis, sinked or not. I see a couple options ... I could mount sinks externally, with a hole cut in the chassis to allow direct contact with the flange. Or I could keep them inside, near an edge, with ventilation holes above and to the side to allow convection. What has worked for you?
Side question - what are y'all's preferred heat sinks for TO-220s? Amazon has a bunch of different inexpensive small sinks, but none of them have any meaningful specifications.
(I've got gobs of heater current to spare, so I've also considered using 6080 pass tubes topside, but that seems unnecessary and expensive.)
I've got a couple of pass mosfets in my power supply design that will be dissipating around 7W apiece. They're in a TO-220 package (although I'm open to others), and have a 62.5C/W thermal resistance in free air, so they need to be sinked.
I obviously can't just stick them inside a closed chassis, sinked or not. I see a couple options ... I could mount sinks externally, with a hole cut in the chassis to allow direct contact with the flange. Or I could keep them inside, near an edge, with ventilation holes above and to the side to allow convection. What has worked for you?
Side question - what are y'all's preferred heat sinks for TO-220s? Amazon has a bunch of different inexpensive small sinks, but none of them have any meaningful specifications.
(I've got gobs of heater current to spare, so I've also considered using 6080 pass tubes topside, but that seems unnecessary and expensive.)
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Why not try aliexpress for heatsinks? You can always drill new holes to cater for your TO3 cases chopping off a couple of fins with a hacksaw will help you out to fit new transistors. Otherwise you can opt for similar devices in TO247 case that can take the same load. A small fan will always help with getting rid of heat. This can be thermally sensed so that it does not make much noise when at light loads.
Mount finned heatsinks to side or back of the supply enclosure, so they are always in free air.
Hundreds of heatsink designs and shapes available, you´ll need something like this:
Artículo 5075 ZD-28
Dimensions:
Base: 104mm
Fin Height: 25.4mm
Core thickness 4,75mm.
Finless center width: 32mm.
Thermal resistance: 2.9º C/W for 75mm height (mounted vertically)
Compact size, no fan needed since sink temperature will rise 14*2.9=40.6 deg. C above ambient temperature.
Do the Math for actual junction rise above that: 7W * Rth JC +1.2 Deg C/W (mica + grease).
EDIT:
An improvement of course, but you must consider the whole chain end to end:
Junction > case > Mica > aluminum HS > air
Hundreds of heatsink designs and shapes available, you´ll need something like this:
Artículo 5075 ZD-28
Dimensions:
Base: 104mm
Fin Height: 25.4mm
Core thickness 4,75mm.
Finless center width: 32mm.
Thermal resistance: 2.9º C/W for 75mm height (mounted vertically)
Compact size, no fan needed since sink temperature will rise 14*2.9=40.6 deg. C above ambient temperature.
Do the Math for actual junction rise above that: 7W * Rth JC +1.2 Deg C/W (mica + grease).
EDIT:
will lower mica+grease Rth to 0.6 or 0.7 Deg C / W
An improvement of course, but you must consider the whole chain end to end:
Junction > case > Mica > aluminum HS > air
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7w dissipation is significant, because that'll be continuous in such a 'pass transistor' configuration
- and the TO220 package is, at best - only good for 15-20w dissipation with optimal heatsinking. Sugget you need a heft lump of external metal /damn solid casework to bolt them to - or explore alternative packages as already suggested for an easier life.
Alternatively - an you take advantage of solving this as a problem?
Is there any useful way you can split that dissipation across two series devices - how about a comparable pair of TO220s dropping roughly half the voltage, either as (say) a cap multiplier perhaps zener-referenced; or a cascoded pair, or similar?
Looking at the thermal dissipation problem sideways could not only spread the total heat disspation usefully, - but also improve the performance of your regulated supply : )
- and the TO220 package is, at best - only good for 15-20w dissipation with optimal heatsinking. Sugget you need a heft lump of external metal /damn solid casework to bolt them to - or explore alternative packages as already suggested for an easier life.
Alternatively - an you take advantage of solving this as a problem?
Is there any useful way you can split that dissipation across two series devices - how about a comparable pair of TO220s dropping roughly half the voltage, either as (say) a cap multiplier perhaps zener-referenced; or a cascoded pair, or similar?
Looking at the thermal dissipation problem sideways could not only spread the total heat disspation usefully, - but also improve the performance of your regulated supply : )
I'm using RAD-A5723 for my regulators, but these need to be drilled and threaded to make them work.2.3K/W so a 15.5K temperature rise over ambient. RAD-A5723/50 STONECOLD - Koellichaam: geextrudeerd | met ribben; zwart; L: 50mm; W: 78mm | TME - Elektronische Componenten
I have a design where i just place these on standoffs on the board.
The industry standard over here seems to be the SK129-50 made by fischer for PCB mounted sinks.
These are 5.3K/W from the top of my head. All things considered these are gonna run 60-70C inside a chassis. so you need a Mosfet that has plenty of SOA to stop it from failing. IXTP80N075L2 could work for low voltage stuff.
6080 pass tubes seems to me the way to go, Ask if you need boardfiles i did a 2x6080 6EJ7(EF184) 0D3 board sometime back. 100x160mm
I have a design where i just place these on standoffs on the board.
The industry standard over here seems to be the SK129-50 made by fischer for PCB mounted sinks.
These are 5.3K/W from the top of my head. All things considered these are gonna run 60-70C inside a chassis. so you need a Mosfet that has plenty of SOA to stop it from failing. IXTP80N075L2 could work for low voltage stuff.
6080 pass tubes seems to me the way to go, Ask if you need boardfiles i did a 2x6080 6EJ7(EF184) 0D3 board sometime back. 100x160mm